UNIVERSITY  OF  ILLINOIS 
LIBRARY 

Class  Book  Volume 

REMOTE  STORAGE 


r 


Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/details/kirkeshandbookofOOkirk_0 


ABSORPTION  SPECTRA 


1.  Spectrum  of  ATgaiid-lamTj  wth  FranTiliofefs  lines  in  position, 

2.  Blood;  I.e.  a  strong  solution  of  OxyhcBraoglobm  ^cieduced.  Haimoglo'bm. 

5.  BIcod  more  dilute. 

4.  Reduced  HffimoglolDin.  5. Carlson  Monoxide  compound. 

6.  Acid  tfematin. "  7.  A].kaline  Hasmatin, 

8.  Sulphuretted  Hydrogen  conipouud,  9.  Ox-bile  acidulated  with  Acetic  acid 
and  colo-urmg  matter  dissolved  in  Chloroforia. 

S/H-ttni  (Innv/i  /ht/n  obst'n'df  to/is  /ly  Jfr.W.  /.rpjuiik,  /"W.  S. 


KIEKES'  HAITD-BOOK  OF  PHYSIOLOGY  '^H-^ 


HAND-BOOK 


OF 


PHYSIOLOGY 


W.  MOEEAISTT  BAKEE,  F.E.C.S. 

SURGEON  TO  ST.  BARTHOLOMEW'S  HOSPITAL  AND  CONSULTING  SURGEON  TO  THE  EVELINA  HOSPITAL 
FOR  SICK  CHILDREN;    LECTURER  ON  PHYSIOLOGY  AT  ST.  BARTHOLOMEW'S  HOSPITAL, 
ANP  LATE  MEMBER  OF  THE  BOARD  OF  EXAMINERS  OF  THE  ROYAL  COLLEGE 
OF  SURGEONS  OF  ENGLAND. 


VINCENT  DORMEE  HARRIS,  M.D.,  Loiro. 

DEMONSTRATOR  OF  PHYSIOLOGY  AT  ST.  BARTHOLOMEW'S  HOSPITAL. 

ELEVENTH  EDITION 
WITH  NEARLY  BOO  ILLUSTRATIONS 


NEW  YOEK 

WILLIAM  WOOD  &  COMPANY 

56  &  58  Lafayette  Place 
18  86  ;^ 


.G3 


The  Publishers' 
Book  Composition  and  Electrotyping  Co., 
39  AND  41  Park  Place, 
New  York. 


REMOTE  STORAGE 
PREFACE  TO  THE  ELEVENTH  EDITION. 


In  the  preparation  of  the  present  edition  of  Kirkes'  Physiology, 
we  have  endeavored  to  maintain  its  character  as  a  guide  for  stu- 
dents, especially  at  an  early  period  of  their  career;  and,  while 
incorporating  new  facts  and  observations  which  are  fairly  estab- 
lished, we  have  as  far  as  possible  omitted  the  controvertible  matters 
which  should  only  find  a  place  in  a  complete  treatise  or  in  a  work  of 
reference. 

A  large  number  of  new  illustrations  have  been  added,  for  many 
of  which  we  are  indebted  to  the  courtesy  of  Dr.  Klein,  Professor 
Michael  Foster,  Professor  Schaefer,  Dr.  Mahomed,  Mr.  Gant,  and 
Messrs.  McMillan,  who  have  been  so  good  as  to  allow  various  figures 
to  be  copied.  Our  thanks  are  also  due  to  Mr„  Wm.  Lapraik,  F.C.S., 
who  has  kindly  prepared  a  table  of  the  absorption  spectra  of  the 
blood  and  bile,  based  upon  his  own  observations;  as  well  as  to  Mr. 
S.  K.  Alcock  for  several  careful  drawings  of  microscopical  prepara- 
tions, and  for  reading  several  sheets  in  their  passage  through  the 
press. 

Mr.  Danielsson,  of  the  firm  of  Lebon  &  Co.,  has  executed  all  the 
new  figures  to  our  entire  satisfaction ;  and  for  the  skill  and  labor  he 
has  expended  upon  them  we  are  much  indebted  to  him. 

We  are  desirous  also  of  acknowledging  the  help  we  have  derived 
from  the  following  works :  Klein's  Histology ;  M.  Foster's  Text-Book 
of  Physiology;  Pavy's  Food  and  Dietetics;  Quain's  Anatomy,  YoL 
II.,  Ed.  ix. ;  Wickham  Legg's  Bile,  Jaundice,  and  Bilious  Diseases; 


iv  PREFACE. 

Watney's  Minute  Anatomy  of  the  Thymus ;  Rosenthal's  Muscles  and 

Nerves  ;  Cadiat's  Traits  D'Anatomie  G6n^rale  ;  Ranvier's  Traits 

Technique  D'Histologie  ;  Landois'  Lehrbuch  der  Physiologie  des 

Mensclien,  and  the  Journal  of  Physiology. 
\ 

W.  MORRANT  BAKER. 
V.  D,  HARRIS. 

WiMPOLE  StKEET, 

August,  1884. 


CHAPTEE  I. 

PAGK 

The  General  and  Distinctive  Characters  op  Living  Beings      .      .  1 

CHAPTER  IL 

Structural  Basis  of  the  Human  Body   5 

Cells   5 

Protoplasm   6 

Nucleus   10 

Intercellular  Substance   17 

Fibres   17 

Tubules   17 

CHAPTER  III. 

Structure  of  the  Elementary  Tissues   .19 

Epithelium     19 

Connective  Tissues   38 

Areolar  Tissue   31 

White  Fibrous  Tissue   31 

Yellow  Elastic  Tissue   32 

Gelatinous                                                                               .  33 

Retiform  or  Adenoid  •      .       .       .  .34 

Neuroglia   34 

Adipose   35 

Cartilage   38 

Bone  ,       ...  43 

Teeth   55 

CHAPTER  IV. 

The  Blood  63 

Quantity  of  Blood  63 

Coagulation  of  the  Blood   65 

Conditions  affecting  Coagulation   .  .71 

The  Blood  Corpuscles   .      .  .74 


vi 


CONTENTS. 


The  Blood — Continued. 

PAGE 

Physical  and  Chemical  Characters  of  Red  Blood-Cells       ....  75 

The  White  Corpuscles,  or  Blood-Leucocytes   79 

Chemical  Composition  of  the  Blood    .       ,   83 

The  Serum    .   85 

Variations  in  Healthy  Blood  under  Different  Circumstances     ...  86 

Variations  in  the  Composition  of  the  Blood  in  Different  Parts  of  the  Body  87 

Gases  contained  in  the  Blood  •       •  .88 

Blood-Crystals   91 

Development  of  the  Blood    96 

Uses  of  the  Blood   99 

Uses  of  the  various  Constituents  of  the  Blood    .      .      .      ,      .  .99 

CHAPTEE  V. 

Circulation  of  the  Blood   101 

The  Systemic,  Pulmonary,  and  Portal  Circulations   102 

The  Forces  concerned  in  the  Circulation  of  the  Blood       ....  103 

The  Heart   103 

Structure  of  the  Valves  of  the  Heart   .       .       .      .       .       .      .       .  Ill 

The  Action  of  the  Heart   Ill 

Function  of  the  Valves  of  the  Heart   .       .   112 

Sounds  of  the  Heart     ...........  117 

Impulse  of  the  Heart                                                                      .  119 

The  Cardiograph   119 

Frequency  and  Force  of  the  Heart's  Action   122 

Influence  of  the  Nervous  System  on  the  Action  of  the  Heart    .       .       .  124 

Effects  of  the  Heart's  Action   .127 

The  Arteries,  Capillaries,  and  Veins   128 

Structure  of  the  Arteries   129 

Structure  of  Capillaries  "  .      .      .       .  133 

Structure  of  Veins   .  .136 

Function  of  the  Arteries                                                                  .  138 

The  Pulse   142 

Sphygmograph     .     '   143 

Pressure  of  the  Blood  in  the  Arteries,  or  Arterial  Tension         .       .       .  148 

The  Kymograph   150 

Influence  of  the  Nervous  System  on  the  Arteries       .       ,      .       .       .  152 

Circulation  in  the  Capillaries   158 

Diapedesis  of  Blood-Corpuscles   159 

Circulation  in  the  Veins     .      ,   IGl 

TBlood-pressure  in  the  Veins  ,      .       .       .  162 

Velocity  of  the  Circulation   163 

Velocity  of  the  Blood  in  the  Arteries   164 

Capillaries   165 

*'        "       "        "       Veins   165 

Velocity  of  the  Circulation  us  a  whole       ......      ^  166 


CONTENTS.  vii 

PAGE 

Peculiarities  of  the  Circulation  in  Different  Parts  ....  167 

Circulation  in  the  Brain   .      .  .167 

Circulation  in  the  Erectile  Structures   168 

Agents  concerned  in  the  Circulation   170 

Discovery  of  the  Circulation   170 

Proofs  of  the  Circulation  of  the  Blood   171 

CHAPTER  VI. 

Respiration                                                                    .      .      .  173 

Position  and  Structure  of  the  Lungs   173 

Structure  of  the  Trachea  and  Bronchial  Tubes   176 

Structure  of  Lobules  of  the  Lungs   178 

Mechanism  of  Respiration    .       .   183 

Respiratory  Movements       .       .   183 

Respiratory  Rhythm   188 

Respiratory  Sounds   188 

Respiratory  Movements  of  Glottis   188 

Quantity  of  Air  Respired   189 

Vital  or  Respiratory  Capacity     .       .   190 

Force  exerted  in  Respiration   191 

Circulation  of  Blood  in  the  Respiratory  Organs   191 

Changes  of  the  Air  in  Respiration   192 

Changes  produced  in  the  Blood  by  Respiration   198 

Mechanism  of  various  Respiratory  Actions        .       .       .     ^      .       .  198 

Influence  of  the  Nervous  System  in  Respiration  .      .      .  *    .      .      .  201 

Effects  of  Vitiated  Air— Ventilation   204 

Effect  of  Respiration  on  the  Circulation   205 

Apnoea— Dyspnoea— Asphyxia  '    .      .  209 

CHAPTER  VII. 

Foods   212 

Classification  of  Foods   213 

Foods  containing  chiefly  Nitrogenous  Bodies      .....  214 

Carbohydrate  Bodies   216 

Fatty  Bodies.      :      .      .      .      .  .217 

Substances  supplying  the  Salts   217 

Liquid  Foods   217 

Effects  of  Cooking   217 

Effects  of  an  Insufficient  Diet   218 

Starvation   219 

Effects  of  Improper  Food   221 

Effects  of  too  much  Food   222 

Diet  Scale   223 

CHAPTER  VIII. 

Digestion   224 

Passage  op  Food  through  the  Alimentary  Canal   224 

Mastication   224 

Insalivation   226 


viii 


CONTENTS. 


Passage  op  Food,  '^tc— Continued. 

PAGE 

The  Salivary  Glands  and  the  Saliva   226 

Structure  of  the  Salivary  Glands   226 

The  Saliva   229 

Influence  of  the  Nervous  System  on  the  Secretion  of  Saliva      .      .  .231 

The  Pharnyx   236 

The  Tonsils   236 

The  (Esophagus  or  Gullet      .      .      .      .   236 

Swallowing  or  Deglutition   238 

Digestion  op  Food  in  the  Stomach    .      .•     .      .      .      ,      .      .  240 

Structure  of  the  Stomach   241 

Gastric  Glands   242 

The  Gastric  Juice   245 

Functions  of  the  Gastric  Juice   247 

Movements  of  the  Stomach   249 

Vomiting   251 

Influence  of  the  Nervous  System  on  Gastric  Digestion      ....  252 

Digestion  of  the  Stomach  after  Death   253 

Digestion  in  the  Intestines   254 

Structure  of  the  Small  Intestine   254 

Valvulae  Conniventes   255 

Glands  of  the  Small  Intestine      .........  257 

The  Villi   259 

Structure  of  the  Large  Intestine   262 

The  Pancreas  and  its  Secretion    .      .       .   264 

Structure  of  the  Liver   268 

Functions  of  the  Liver   273 

The  Bile   273 

The  Liver  as  a  Blood-elaborating  Organ   280 

Glycogenic  Function  of  the  Liver   280 

Summary  of  the  Changes  which  take  place  in  the  Food  during  its  Passage 

through  the  Small  Intestine   284 

Succus  Entericus   283 

Summary  of  the  Process  of.  Digestion  in  the  Large  Intestine     .       .       .  286 

Defeecation   288 

Gases  contained  in  the  Stomach  and  Intestines   288 

Movements  of  the  Intestines   289 

Influence  of  the  Nervous  System  on  Intestinal  Digestion  ....  290 

CHAPTER  IX. 

Absokptton   291 

.  The  Lacteal  and  Lymphatic  Vessels  and  Glands   291 

Lym])hati(;  Glands   297 

Properties  of  Lymph  and  Chyle   301 

Absorption  by  tlie  Lacteal  Vessels   303 

Absorption  by  tlic  Lymphatic  Vessels   303 

Absorption  by  Bioodrvesscls   305 


CONTENTS. 


IX 


CHAPTER  X. 

PAGE 

Animal  Heat   309 

Variations  in  Bodily  Temperature   309 

Sources  of  Heat   311 

Loss  of  Heat   313 

Production  of  Heat   315 

Inhibitory  Heat-centre   316 


CHAPTEE  XL 

Secretion   317 

Secreting  Membranes   319 

Serous  Membranes   319 

Mucous  Membranes   .      .    321 

Secreting  Glands  • .      .      .      .  322 

Process  of  Secretion   324 

Circumstances  influencing  Secretion  .      .      .      .      .      .      .  326 

Mammary  Glands  and  their  Secretion   328 

Chemical  Composition  of  Milk   331 


CHAPTEE  XIL 

The  Skin  and  its  Functions  333 

Structure  of  the  Skin  •       •       •  .333 

Sudoriparous  Glands  337 

Sebaceous  Glands   .       .  "     .       .       .       .  339 

Structure  of  Hair   .       .       .  .339 

Structure  of  Nails   341 

Functions  of  the  Skin  342 


CHAPTEE  XIII. 


The  Kidneys  and  Urine   347 

Structure  of  the  Kidneys   347 

Structure  of  the  Ureter  and  Urinary  Bladder   354 

The  Urine   355 

The  Secretion  of  Urine  •  ....  365 

Micturition  .      .      ,   373 


♦ 


r 


I 


i 

I 

I 
( 


CHAPTER  I. 

THE  GENERAL  AND  DISTINCTIVE  CHARACTERS  OF  LIVING 

BEINGS. 

Human  Physiology  is  the  science  which  treats  of  the  life  of  man — 
of  the  way  in  which  he  lives^  and  moves,  and  has  his  being.  It  teaches 
how  man  is  begotten  and  born;  how  he  attains  maturity;  and  liow  he 
dies. 

Having,  then,  man  as  the  object  of  its  study,  it  is  unnecessary  to  speak 
here  of  the  laws  of  life  in  general,  and  the  means  by  which  they  are  car- 
ried out,  further  than  is  requisite  for  the  more  clear  understanding  of 
those  of  the  life  of  man  in  particular.  Yet  it  would  be  impossible  to 
understand  rightly  the  working  of  a  complex  machine  without  some 
knowledge  of  its  motive  power  in  the  simplest  form;  and  it  may  be  well 
to  see  first  what  are  the  so-called  essentials  of  life — those,  namely,  which 
are  manifested  by  all  living  beings  alike,  by  the  lowest  vegetable  and  the 
highest  animal — before  proceeding  to  the  consideration  of  the  structure 
and  endowments  of  the  organs  and  tissue  belonging  to  man. 

The  essentials  of  life  are  these, — Birth,  Groivtli  and  Development,, 
Decline  and  Death. 

The  term  birth,  when  employed  in  this  general  sense  of  one  of  the 
conditions  essential  to  life,  without  reference  to  any  particular  kind  of 
living  being,  may  be  taken  to  mean,  separation  from  a  parent,  with  a. 
greater  or  less  power  of  independent  life.  Taken  thus,  the  term, 
although  not  defining  any  particular  stage  in  development,  serves  well 
enough  for  the  expression  of  the  fact,  to  which  no  exception  has  yet  been, 
proved  to  exist,  that  the  capacity  for  life  in  all  living  beings  is  obtained, 
by  inheritance. 

Growth,  or  inherent  power  of  increasing  in  size,  although  essential 
to  our  idea  of  life,  is  not  confined  to  living  beings.    A  crystal  of  common 
salt,  or  of  any  other  similar  substance,  if  placed  under  appropriate  condi- 
VoL.  I.— 1. 


2 


HAND-BOOK  OF  PHYSIOLOGY. 


tions  for  obtaining  fresh  material,  will  grow  in  a  fashion  as  definitely  char- 
acteristic and  as  easily  to  be  foretold  as  that  of  a  living  creature.  It  is, 
therefore,  necessary  to  explain  the  distinctions  which  exist  in  this  respect 
between  living  and  lifeless  structures;  for  the  manner  of  growth  in  the 
two  cases  is  widely  different. 

Differences  between  Living  and  Lifeless  Growth. — (1.)  The 
growth  of  a  crystal,  to  use  the  same  example  as  before,  takes  place  merely 
by  additions  to  its  outside;  the  new  matter  is  laid  on  particle  by  particle, 
and  layer  by  layer,  and,  when  once  laid  on,  it  remains  unchanged.  The 
growth  is  here  said  to  be  superficial.  In  a  living  structure,  on  the  other 
hand,  as,  for  example,  a  brain  or  a  muscle,  where  growth  occurs,  it  is  by 
addition  of  new  matter,  not  to  the  surface  only,  but  throughout  every 
part  of  the  mass;  the  growth  is  not  superficial,  but  interstitial. 

(2.)  All  living  structures  are  subject  to  constant  decay;  and  life  con- 
sists not,  as  once  supposed,  in  the  power  of  preventing  this  never-ceasing 
decay,  but  rather  in  making  up  for  the  loss  attendant  on  it  by  never- 
ceasing  repair.  Thus,  a  man's  body  is  not  composed  of  exactly  the  same 
particles  day  after  day,  although  to  all  intents  he  remains  the  same  indi- 
vidual. Almost  every  part  is  changed  by  degrees;  but  the  change  is  so 
gradual,  and  the  renewal  of  that  which  is  lost  so  exact,  that  no  difference 
may  be  noticed,  except  at  long  intervals  of  time.  A  lifeless  structure, 
-as  a  crystal,  is  subject  to  no  such  laws;  neither  decay  nor  repair  is  a 
necessary  condition  of  its  existence.  That  which  is  true  of  structures 
"which  never  had  to  do  with  life  is  true  also  with  respect  to  those  w^hich, 
though  they  are  formed  by  living  parts,  are  not  themselves  alive.  Thus, 
an  oyster-shell  is  formed  by  the  living  animal  which  it  encloses,  but  it  is 
as  lifeless  as  any  other  mass  of  inorganic  matter;  and  in  accordance  with 
this  circumstance  its  growth  takes  place,  not  inter sf it i ally ,  but  layer  by 
layer,  and  it  is  not  subject  to  the  constant  decay  and  reconstruction  which 
belong  to  the  living.    The  hair  and  nails  are  examples  of  the  same  fact. 

(3.)  In  connection  with  the  growth  of  lifeless  masses  there  is  no  alter- 
ation in  the  chemical  constitution  of  the  material  which  is  taken  up  and 
added  to  the  previously  existing  mass.  For  example,  when  a  crystal  of 
common  salt  grows  on  being  placed  in  a  fluid  which  contains  the  same 
material,  the  properties  of  the  salt  are  not  clianged  by  being  taken  out  of 
the  liquid  by  the  crystal  and  added  to  its  surface  in  a  solid  form.  But 
the  case  is  essentially  different  in  living  beings,  botli  animal  and  vegeta- 
])le.  A  plant,  like  a  crystal,  can  only  grow  wlicn  fresh  material  is  pre- 
sented to  it;  and  this  is  absorbed  by  its  leaves  and  roots;  and  auinuds, 
for  the  same  purpose  of  getting  new  matter  for  growtli  and  nutrition, 
take  food  into  tlieir  stomachs.  But  in  both  tliese  cases  the  nuitorials  are 
much  altered  before  tliey  are  finally  assimilated  by  the  structures  they 
are  destined  to  nourish. 

(4.)  Tlie  growtli  of  all  living  things  has  a  dolinile  limit,  and  the  law 


DlSTmCTlVE  ClIAKACTEKti  OF  LIVING  BEINGS. 


3 


which  governs  this  limitation  of  increase  in  size  is  so  invariable  that  we 
should  be  as  much  astonished  to  find  an  individual  x>iant  or  animal  with- 
out limit  as  to  growth  as  without  limit  to  life. 

Development  is  as  constant  an  accompaniment  of  life  as  growth.  The 
term  is  used  to  indicate  that  change  to  which,  before  maturity,  all  living 
parts  are  constantly  subject,  and  by  which  they  are  made  more  and  more 
capable  of  performing  their  several  functions.  For  example,  a  full-grown 
man  is  not  merely  a  magnified  child ;  his  tissues  and  organs  have  not  only 
grown,  or  increased  in  size,  they  have  also  developed,  or  become  better  in 
quality. 

No  very  accurate  limit  can  be  drawn  between  the  end  of  development 
and  the  beginning  of  decline;  and  the  two  processes  may  be  often  seen 
together  in  the  same  individual.  But  after  a  time  all  parts  alike  share 
in  the  tendency  to  degeneration,  and  this  is  at  length  succeeded  by  death. 

Differences  between  Plants  and  Animals. — It  has  been  already 
said  that  the  essential  features  of  life  are  the  same  in  all  living  things; 
in  other  words,  in  the  members  of  both  the  animal  and  vegetable  king- 
doms. It  may  be  well  to  notice  briefly  the  distinctions  which  exist  be- 
tween the  members  of  these  two  kingdoms.  It  may  seem,  indeed,  a 
strange  notion  that  it  is  possible  to  confound  vegetables  with  animals, 
but  it  is  true  with  respect  to  the  lowest  of  them,  in  which  but  little  is 
manifested  beyond  the  essentials  of  life,  whi^^h  are  the  same  in  both. 

(1.)  Perhaps  the  most  essential  distinction  is  the  presence  or  absence 
of  power  to  live  upon  inorganic  material.  By  means  of  their  green  color- 
ing matter,  c]iloroj)hyl — a  substance  almost  exclusively  confined  to  the 
vegetable  kingdom,  plants  are  capable  of  decomposing  the  carbonic  acid, 
ammonia,  and  water,  which  they  absorb  by  their  leaves  and  roots,  and 
thus  utilizing  them  as  food.  The  result  of  this  chemical  action,  which 
occurs  only  under  the  influence  of  light,  is,  so  far  as  the  carbonic  acid  is 
concerned,  the  fixation  of  carbon  in  the  plant  structures  and  the  exhala- 
tion of  oxygen.  Animals  are  incapable  of  thus  using  inorganic  matter, 
and  never  exhale  oxygen  as  a  product  of  decomposition. 

The  power  of  living  upon  organic  as  well  as  inorganic  matter  is  less 
decisive  of  an  animal  nature;  inasmuch  as  fungi  and  some  other  plants 
derive  their  nourishment  in  part  from  the  former  source. 

(2.)  There  is,  commonly,  a  marked  difference  in  general  chemical 
composition  between  vegetables  and  animals,  even  in  their  lowest  forms; 
for  while  the  former  consist  mainly  of  cellulose,  a  substance  closely  allied 
to  starch  and  containing  carbon,  hydrogen,  and  oxygen  only,  the  latter 
are  composed  in  great  part  of  the  three  elements  just  named,  together 
with  a  fourth,  nitrogen;  the  chief  proximate  principles  formed  from 
these  being  identical,  or  nearly  so,  with  albumen.  It  must  not  be  sup- 
posed, however,  that  either  of  these  typical  compounds  alone,  with  its 
allies,  is  <^-onfined  to  one  kingdom  of  nature.    Nitrogenous  compounds 


4 


HAND-BOOK  OF  PHYSIOLOGY. 


are  freely  produced  in  vegetable  structures,  although  they  form  a  very 
much  smaller  proportion  of  the  whole  organism  than  cellulose  or  starch. 
And  while  the  presence  of  the  latter  in  animals  is  much  more  rare  than 
is  that  of  the  former  in  vegetables,  there  are  many  animals  in  which 
traces  of  it  may  be  discovered,  and  some,  the  Ascidians,  in  which  it  is 
found  in  considerable  quantity. 

(3.)  Inherent  power  of  movement  is  a  quality  which  we  so  commonly 
consider  an  essential  indication  of  animal  natare,  that  it  is  difficult  at 
first  to  conceive  it  existing  in  any  other.  The  capability  of  simple  motion 
is  now  known,  however,  to  exist  in  so  many  vegetable  forms,  that  it  can 
no  longer  be  held  as  an  essential  distinction  between  them  and  animals, 
and  ceases  to  be  a  mark  by  which  the  one  can  be  distinguished  from  the 
other.  Thus  the  zoospores  of  many  of  the  Cryptogamia  exhibit  ciliary 
or  amoeboid  movements  (p.  8)  of  a  like  kind  to  those  seen  in  animalcules; 
and  even  among  the  higher  orders  of  plants,  many,  e.  g.,  Dioncea  Mus- 
cipula  (Venus's  fly-trap),  and  Mimosa  Sensitiva  (Sensitive  plant),  exhibit 
such  motion,  either  at  regular  times,  or  on  the  application  of  external 
irritation,  as  might  lead  one,  were  this  fact  taken  by  itself,  to  regard 
them  as  sentient  beings.  Inherent  power  of  movement,  then,  although 
especially  characteristic  of  animal  nature,  is,  when  taken  by  itself,  no 
proof  of  it. 

(4.)  The  presence  of  a  digestive  canal  is  a  very  general  mark  by 
which  an  animal  can  be  distinguished  from  a  vegetable.  But  the  lowest 
animals  are  surrounded  by  material  that  they  can  take  as  food,  as  a  plant 
is  surrounded  by  an  atmosphere  that  it  can  use  in  like  manner.  And 
every  part  of  their  body  being  adapted  to  absorb  and  digest,  they  have 
no  need  of  a  special  receptacle  for  nutrient  matter,  and  accordingly  have 
no  digestive  canal.    This  distinction  then  is  not  a  cardinal  one. 

It  would  be  tedious  as  well  as  unnecessary  to  enumerate  the  chief  dis- 
tinctions between  the  more  highly  developed  animals  and  vegetables. 
They  are  sufficiently  apparent.  It  is  necessary  to  compare,  side  by  side, 
the  lowest  members  of  the  two  kingdoms,  in  order  to  understand  rightly 
how  faint  are  the  boundaries  between  them. 


CHAPTER  II. 


STRUCTURAL  BASIS  OF  THE  HUMAN  BODY. 

By  dissection,  the  human  body  can  be  proved  to  consist  of  various  dis- 
similar parts,  bones,  muscles,  brain,  heart,  lungs,  intestines,  etc.,  while, 
on  more  minute  examination,  these  are  found  to  be  composed  of  different 
tissues,  such  as  the  connective,  epithelial,  nervous,  muscular,  and  the 
like. 

Cells. — Embryology  teaches  us  that  all  this  complex  organization  has 
been  developed  from  a  microscopic  body  about  yl-^  in.  in  diameter 
(ovum),  which  consists  of  a  spherical  mass  of  jelly-like  matter  enclosing 
a  smaller  spherical  body  (germinal  vesicle).  Further,  each  individual 
tissue  can  be  shown  largely  to  consist  of  bodies  essentially  similar  to  an 
ovum,  though  often  differing  from  it  very  widely  in  external  form.  They 
are  termed  cells :  and  it  must  be  at  once  evident  that  a  correct  knowledge 
of  the  nature  and  activities  of  the  cell  forms  the  very  foundation  of 
physiology. 

Cells  are,  in  fact,  physiological  no  less  than  histological  units. 

The  prime  importance  of  the  cell  as  an  element  of  structure  was  first 
established  by  the  researches  of  Schleiden,  and  his  conclusions,  drawn 
from  the  study  of  vegetable  histology,  were  at  once  extended  by  Schwann 
to  the  animal  kingdom.  The  earlier  observers  defined  a  cell  as  a  more  or 
less  spherical  body  limited  by  a  membrane,  and  containing  a  smaller  body 
termed  a  nucleus,  which  in  its  turn  encloses  one  or  more  nucleoli.  Such 
a  definition  applied  admirably  to  inost  vegetable  cells,  but  the  more 
extended  investigation  of  animal  tissues  soon  showed  that  in  many  cases 
no  limiting  membrane  or  cell-wall  could  be  demonstrated. 

The  presence  or  absence  of  a  cell-wall,  therefore,  was  now  regarded  as 
quite  a  secondary  matter,  while  at  the  same  time  the  cell-substance  came 
gradually  to  be  recognized  as  of  primary  importance.  Many  of  the  lower 
forms  of  animal  life,  e.g.,  the  Rhizopoda,were  found  to  consist  almost  entire- 
ly of  matter  very  similar  in  appearance  and  chemical  composition  to  the 
cell-substance  of  higher  forms:  and  this  from  its  chemical  resemblance  to 
flesh  was  termed  Sarcode  by  Dujardin.  When  recognized  in  vegetable 
cells  it  was  called  Protoplasm  by  Mulder,  while  Remak  applied  the  same 
name  to  the  substance  of  animal  cells.  As  the  presumed  formative  mat- 
ter in  animal  tissues  it  was  termed  Blastema,  and  in  the  belief  that, 
wherever  found,  it  alone  of  all  substances  has  to  do  with  generation  and 


6 


HAT^D-BOOK  OF  PHYSIOLOGY. 


nutrition,  Beale  lias  named  it  Germinal  matter  or  Bioplasm.  Of  these 
terms  the  one  most  in  vogue  at  the  present  day  is  Protoplasm,  and  inas- 
much as  all  life,  both  in  the  animal  and  vegetable  kingdoms,  is  associated 
with  protoplasm,  we  are  justified  in  describing  it,  with  Huxley,  as  the 
^'physical  basis  of  life.*' 

A  cell  may  now  be  defined  as  a  nucleated  mass  of  protoplasm,^  of 
microscopic  size,  which  possesses  sufiicient  individuality  to  have  a  life- 
history  of  its  own.  Each  cell  goes  through  the  same  cycle  of  changes 
as  the  whole  organism,  though  doubtless  in  a  much  shorter  time.  Begin- 
ning with  its  origin  from  some  pre-existing  cell,  it  grows,  produces  other 
cells,  and  finally  dies.  It  is  true  that  several  lower  forms  of  life  consist  of 
non-nucleated  protoplasm,  but  the  above  definition  holds  good  for  all 
the  higher  plants  and  animals. 

Hence  a  summary  of  the  manifestations  of  cell-life  is  really  an  account 
of  the  vital  activities  of  protoplasm. 

Protoplasm. — P/^ ^6- /Vr// characters. — Physically,  protoplasm  is  viscid, 
varying  in  consistency  from  semi-fluid  to  strongiyc  oherent.  Chemical 
characters. — Chemically,  living  protoplasm  is  an  extremely  unstable  albu- 
minoid substance,  insoluble  in  water.  It  is  neutral  or  weakly  alkaline  in 
reaction.  It  undergoes  heat  stiffening  or  coagulation  at  about  130°F. 
(54'5'^C.),  and  hence  no  organism  can  live  when  its  own  temperature  is 
raised  beyond  this  point,  though,  of  course,  many  can  exist  for  a  time  in 
a  much  hotter  atmosi^here,  since  they  possess  the  means  of  regulating 
their  own  temperature.  Besides  the  coagulation  produced  by  heat,  pro- 
toplasm is  coagulated  by  all  the  reagents  which  produce  this  change  in 
albumen.  If  not-living  protoplasm  be  subjected  to  chemical  analysis  it 
is  found  to  be  made  up  of  numerous  bodies  ^  besides  albumen,  e.g. ,  of  gly- 
cogen, lecithin,  salts  and  water,  so  that  if  living  protoplasm  be,  as  some 
believe,  an  independent  chemical  body,  when  it  no  longer  possesses  life, 
it  undergoes  a  disintegration  which  is  accompanied  by  the  appearance  of 
these  new  chemical  substances.  When  it  is  examined  under  the  micro- 
scope two  varieties  of  protoplasm  are  recognized — the  hyaline,  and  the 
granular.  Both  are  alike  transparent,  but  the  former  is  perfectly  homo- 
geneous, while  the  latter  (the  more  common  variety)  contains  small  gran- 
ules or  molecules  of  various  sizes  and  shapes.  Globules  of  watery  fluid 
are  also  sometimes  found  in  protoplasm;  they  look  like  clear  spaces  in  it, 
and  are  hence  called  vacuoles. 

Vital  or  Pliysiological  characters. — These  may  be  conveniently  treated 
uuder  the  three  heads  of — I.  Motion;  II.  Nutrition;  and  III.  Repro- 
duction. 


'  In  the  Immiin  ])()(ly  the  cells  rango  from  tlio  red  blood-cell  (-^\y^  in.)  to  the  gang- 
lion-cell    ?,  „) 

For  jin  ticcount  of  which,  reference  should  be  made  to  the  Append|jx. 


STRUCTURAL   BASIS  OF  THE  HUMAN  BODY. 


7 


■{a)  Fluent  and  (h) 


I.  Motion. — It  is  probable  that  the  protoplasm  of  all  cells  is  capable 
at  some  time  of  exhibiting  movement;  at  any  rate  this  phenomenon, 
which  not  long  ago  was  regarded  as  quite  a  curiosity,  has  been  recently 
observed  in  cells  of  many  different  kinds.  It  may  be  readily  studied  in 
the  Amoebge,  in  the  colorless  blood -cells  of  all  vertebrata,  in  the  branched 
cornea-cells  of  the  frog,  in  the  hairs  of  the  stinging-nettle  and  Trades- 
cantia,  and  the  cells  of  Vallisneria  and  Chara. 

These  motions  may  be  divided  into  two  classes- 
Ciliary. 

Another  variety — the  molecular  or  vibratory — has  also  been  classed  by 
some  observers  as  vital,  but  it  seems  exceedingly  probable  that  it  is 
nothing  more  than  the  well-known  "Brownian^^  molecular  movement,  a 
purely  mechanical  phenomenon  which  may  be  observed  in  any  minute 
particles,  e.g.,  of  gamboge,  suspended  in  a  fluid  of  suitable  density,  such 
as  water. 

Such  particles  are  seen  to  oscillate  rapidly  to  and  fro,  and  not  to  pro- 
gress in  any  definite  direction. 

(a.)  Fluent. — This  movement  of  protoplasm  is  rendered  perceptible 
(1)  by  the  motion  of  the  granules,  which  are  nearly  always  imbedded  in 
it,  and  (2)  by  changes  in  the  outline  of 
its  mass. 

If  part  of  a  hair  of  Tradescantia 
(Fig.  1)  be  viewed  under  a  high  magni- 
fying power,  streams  of  protoplasm  con- 
taining crowds  of  granules  hurrying 
along,  like  the  foot  passengers  in  a  busy 
street,  are  seen  flowing  steadily  in  defi- 
nite directions,  some  coursing  round 
the  film  which  lines  the  interior  of  the 
cell- wall,  and  others  flowing  toward  or 
away  from  the  irregular  mass  in  the 
centre  of  the  cell-cavity.    Many  of  these 

streams  of  protoplasm  run  together  into  larger  ones,  and  are  lost 
the  central  mass,  and  thus  ceaseless  variations  of  form  are  produced. 

In  the  Amoeba,  a  minute  animal  consisting  of  a  shapeless  and  struc- 
tureless mass  of  sarcode,  an  irregular  mass  of  protoplasm  is  gradually 
thrust  out  from  the  main  body  and  retracted:  a  second  mass  is  then  pro- 
truded in  another  direction,  and  gradually  the  whole  protoplasmic  sub- 
stance is,  as  it  were,  drawn  into  it.  The  Amoeba  thus  comes  to  occupy  a 
new  position,  and  when  this  is  repeated  several  times  we  have  locomotion 
in  a  definite  direction,  together  with  a  continual  change  of  form.  These 
movements  when  observed  in  other  cells,  such  as  the  colorless  blood- 
corpuscles  of  higher  animals  (Fig.  2)  are  hence  termed  ammhoid. 

Colorless  blood-corpuscles  were  first  observed  to  migrate,  i.e.,  pass 


Fig.  1. — Cell  of  Tradescantia  drawn  at 
successive  intervals  of  two  minutes.  The 
cell-contents  consist  of  a  central  mass  con- 
nected by  many  irregular  processes  to  a 
peripheral  film:  the  whole  forms  a  vacuo- 
lated mass  of  protoplasm,  which  is  continu- 
ally changing  its  shape.  (Schofield.) 


m 


8 


HAND-BOOK  OF  PHYSIOLOGY. 


through  the  walls  of  the  blood-vessels  (p.  159),  by  Waller,  whose  obser- 
vations were  confirmed  and  extended  to  connective  tissue  corpuscles  by 
the  researches  of  Recklinghausen,  Oohnheim,  and  others,  and  thus  the 
phenomenon  of  migration  has  been  proved  to  play  an  important  part  in 
many  normal,  and  pathological  processes,  especially  in  that  of  inflam- 
mation. 

This  amoeboid  movement  enables  many  of  the  lower  animals  to  capture 
their  prey,  which  they  accomplish  by  simply  flowing  round  and  enclosing  it. 

The  remarkable  motions  of  pigment-granules  observed  in  the  branched 
pigment-cells  of  the  frog^s  skin  by  Lister  are  probably  due  to  amoeboid 
movement.  These  granules  are*  seen  at  one  time  distributed  uniformly 
through  the  body  and  branched  processes  of  the  cell,  while  under  the 
action  of  various  stimuli  (e.g.,  light  and  electricity)  they  collect  in  the 
central  mass,  leaving  the  branches  quite  colorless. 

(b.)  Ciliary  action  must  be  regarded  as  only  a  special  variety  of  the 
general  motion  with  which  all  protoplasm  is  endowed. 

The  grounds  for  this  view  are  the  following:  In  the  case  of  the  Infu- 
soria, which  move  by  the  vibration  of  cilia  (microscopic  hair-like  processes 
projecting  from  the  surface  of  their  bodies)  it  has  been  proved  that  these 
are  simply  processes  of  their  protoplasm  protruding  through  pores  of  the 


Fig.  2.— Human  colorless  blood-corpuscle,  showing  its  successive  changes  of  outline  within  ten 
minutes  when  kept  moist  on  a  warm  stage.  (Schofield.) 


investing  membrane,  like  the  oars  of  a  galley,  or  the  head  and  legs  of  a 
tortoise  from  its  shell:  certain  reagents  cause  them  to  be  partially  re- 
tracted. Moreover,  in  some  cases  cilia  have  been  observed  to  develop  from, 
and  in  others  to  be  transformed  into,  amoeboid  processes. 

The  movements  of  protoplasm  can  be  very  largely  modified  or  even 
suspended  by  external  conditions,  of  which  the  following  are  the  most 
important. 

1.  Changes  of  temperature. — Moderate  heat  acts  as  a  stimulan^:  tliis 
is  readily  observed  in  the  activity  of  the  movements  of  a  human  colorless 
blood-corpuscle  when  placed  under  conditions  in  which  its  normal  tem- 
perature and  moisture  are  preserved.  Extremes  of  heat  and  cold  stop  the 
motions  entirely. 

2.  Meclumical  stimnh. — When  gently  squeezed  between  a  cover  and 
object  glass  under  proper  conditions,  a  colorless  blood-corpuscle  is  stimu- 
lated to  active  amoeboid  movement. 

3.  Nerve  iiiflnence. — By  stimulation  of  the  nerves  of  tlie  frog's  cornea, 
contraction  of  certain  of  its  branclied  cells  lias  been  i)rodueed. 

4.  Chemical  stimuli. — Water  generally  stojjs  anuvboid  movement,  ami 
by  inil)il)iti()n  causes  great  swelling  ;uul  fnially  bursting  of  the  cells. 


STRUCTURAL   BASIS  OF  THE  HUMAN  BODY. 


9 


In  some  cases,  however,  (myxomycetes)  protoplasm  can  he  almost 
enth-ely  dried  up,  and  is  yet  capable  of  renewing  its  motions  when  again 
moistened. 

Dilute  salt-solution  and  many  dilute  acids  and  alkalies,  stimulate  the 
movements  temporarily. 

Ciliary  movement  is  suspended  in  an  atmosphere  of  hydrogen  or  car- 
bonic acid,  and  resumed  on  the  admission  of  air  or  oxygen. 

5.  Electrical. — Weak  currents  stimulate  the  movement,  while  strong 
currents  cause  the  corpuscles  to  assume  a  spherical  form  and  to  become 
motionless. 

II.  Nutrition. — The  nutrition  of  cells  will  be  more  appropriately 
described  in  the  chapters  on  Secretion  and  Nutrition. 

Before  describing  the  Keproduction  of  cells  it  will  be  necessary  to  con- 
sider their  structure  more  at  length. 

Minute  Structure  of  Cells.— (a.)  — We  have  seen  (p.  5) 

that  the  presence  of  a  limiting-membrane  is  no  essential  part  of  the  defini- 
tion of  a  cell. 

In  nearly  all  cells  the  outer  layer  of  the  protoplasm  attains  a  firmer 
consistency  than  the  deeper  portions:  the  individuality  of  the  cell  be- 
coming more  and  more  clearly  marked  as  this  cortical  layer  becomes  more 
and  more  differentiated  from  the  deeper  portions  of  cell-substance.  Side 
by  side  with  this  physical,  there  is  a  gradual  chemical  differentiation,  till 
at  length,  as  in  the  case  of  the  fat-cells,  we  have  a  definite  limiting-mem- 
brane differing  chemically  as  well  as  physically  from  the  cell-contents, 
and  remaining  as  a  shriveled-up  bladder  when  they  have  been  removed. 
Such  a  membrane  is  transparent  and  structureless,  flexible,  and  per- 
meable to  fluids. 

The  cell-substance  can,  therefore,  still  be  nourished  by  imbibition 
thr(fugh  the  cell- wall.  In  many  cases  (especially  in  fat)  a  membrane  of 
some  toughness  is  absolutely  necessary  to  give  to  the  tissue  the  requisite 
consistency.  When  these  membranes  attain  a  certain  degree  of  thickness 
and  independence  they  are  termed  capsules:  as  examples,  we  may  cite  the 
capsules  of  cartilage-cells,  and  the  thick,  tough  envelope  of  the  ovum 
termed  the  ' 'primitive  chorion. 

(b.)  Cell  contents. — In  accordance  with  their  respective  ages,  positions, 
and  functions,  the  contents  of  cells  are  very  varied. 

The  original  protoplasmic  substance  may  undergo  many  transforma- 
tions; thus,  in  fat-cells  we  may  have  oil,  or  fatty  crystals,  occupying 
nearly  the  whole  cell-cavity:  in  pigment-cells  we  find  granules  of  pig- 
ment; in  the  various  gland-cells  the  elements  of  their  secretions. 
Moreover,  the  original  protoplasmic  contents  of  the  cell  may  undergo  a 
gradual  chemical  change  with  advancing  age;  thus  the  protoplasmic  cell- 
substance  of  the  deeper  layers  of  the  epidermis  becomes  gradually  con- 
verted into  keratin  as  the  cell  approaches  the  surface.    So,  too,  the  orig- 


10 


HAND-BOOK  OF  PHYSIOLOGY. 


inal  protoplasm  of  the  embryonic  blood-cells  is  replaced  by  the  haemo- 
globin of  the  mature  colored  blood-corpuscle. 

The  minute  structure  of  cells  has  lately  been  made  the  subject  of  care- 
ful investigation,  and  what  was  once  regarded  as  homogeneous  proto- 
plasm with  a  few  scattered  granules,  has  been  stated  to  be  an  exceedingly 
complex  structure.  In  colorless  blood-corpuscles,  epithelial  cells,  con- 
nective tissue  corpuscles,  nerve-cells,  and  many  other  varieties  of  cells, 
an  intracellular  netiuorlc  of  very  fine  fibrils,  the  meshes  of  which  are 
occupied  by  a  hyaline  interstitial  substance,  has  been  demonstrated 
(Heitzmann^s  network)  (Fig.  3).  At  fee  nodes,  where  the  fibrils  cross, 
are  little  swellings,  and  these  are  the  objects  described  as  granules  by 
the  older  observers:  but  in  some  cells,  e.g.,  colorless  blood  corpuscles, 
there  are  real  granules,  which  appear  to  be  quite  free  and  unconnected 
with  the  intra-cellular  network. 

(c.)  Nucleus. — Nuclei  (Fig.  3)  were  first  pointed  out  in  the  year  1833, 
by  Robert  Brown,  who  observed  them  in  vegetable  cells.    They  are  either 


Pi&.  3.  —  (a).  Colorless  blood-corpuscle  showing  intra-cellular  network  of  Heitzmann,  and  two 
nuclei  with  intra-nuclear  network.    (Klein  and  Noble  Smith.) 

(B.)  Colored  blood-corpuscle  of  newt  showing  intra-ceUular  network  of  fibrils  (Heitzmann).  Also 
oval  nucleus  composed  of  hmiting-membrane  and  fine  intra-nuclear  network  of  fibrils,  x  800.  (lOein 
and  Noble  Smith.) 

small  transparent  vesicular  bodies  containing  one  or  more  smaller  particles 
(nucleoli),  or  they  are  semi-solid  masses  of  protoplasm  always  in  the 
resting  condition  bounded  by  a  well-defined  envelope.  In  their  relation 
to  the  life  of  the  cell  they  are  certainly  hardly  second  in  importance  to 
the  protoplasm  itself,  and  thus  Beale  is  fully  justified  in  comprising  both 
under  the  term  ^'germinal  matter."  They  exhibit  their  vitality  by  ini- 
tiating the  process  of  division  of  the  cell  into  two  or  more  cells  (fission) 
by  first  themselves  dividing.  Distinct  observations  have  been  made  show- 
ing that  spontaneous  changes  of  form  may  occur  in  nuclei  as  also  in  nu- 
cleoli. 

Histologists  have  long  recognized  nuclei  by  two  important  charac- 
ters:— 

(1.)  Their  poAver  of  resisting  the  action  of  various  acids  and  alkalies, 
particularly  acetic  acid,  by  which  their  outline  is  more  clearly  deliiiod, 
and  they  are  rendered  more  easily  visible.    This  indicates  some  chemical 


STKUCTUKAL   BASIS  OF  THE  HUMAN  BODY. 


11 


difference  between  the  protoplasm  of  the  cell  and  nuclei,  as  the  former  is 
destroyed  by  these  reagents. 

(2.)  Their  quality  of  staining  in  solutions  of  carmine,  hsematoxylin, 
etc.  Nuclei  are  most  commonly  oval  or  round,  and  do  not  generally 
conform  to  the  diverse  shapes  of  the  cells;  they  are  altogether  less  varia- 
ble elements  than  cells,  even  in  regard  to  size,  of  which  fact  one  may  see 
a  good  example  in  the  uniformity  of  the  nuclei  in  cells  so  multiform  as 
those  of  epithelium.  But  sometimes  nuclei  appear  to  occupy  the  whole 
of  the  cell,  as  is  the  case  in  the  lymph  corpuscles  of  lymphatic  glands 
and  in  some  small  nerve  cells. 

Their  position  in  the  cell  is  very  variable.  In  many  cells,  especially 
where  active  growth  is  progressing,  two  or  more  nuclei  are  present. 

The  nuclei  of  many  cells  have  been  shown  to  contain  a  fine  intra- 
nuclear networh  in  every  respect  similar  to  that  described  above  as  intra- 
cellular (Fig.  3),  the  interstices  of  which  are  occupied  by  semi-fluid  pro- 
toplasm. 

III.  Reproduction. — The  life  of  individual  cells  is  probably  very 
short  in  comparison  with  that  of  the  organism  they  compose:  and  their 
constant  decay  and  death  necessitate  constant  reproduction.  The  mode 
in  which  this  takes  place  has  long  been  the  subject  of  great  controversy. 

In  the  case  of  plants,  all  of  whose  tissues  are  either  cellular  or  com- 
posed of  cells  which  are  modified  or  have  coalesced  in  various  ways,  the 
theory  that  all  new  cells  are  derived  from  pre-existing  ones  was  early  ad- 
vanced and  very  generally  accepted.  But  in  the  case  of  animal  tissues 
Schwann  and  others  maintained  a  theory  of  spontaneous  or  free  cell  for- 
mation. 

According  to  this  view  a  minute  corpuscle  (the  future  nucleolus) 
springs  up  spontaneously  in  a  structureless  substance  (blastema)  very  much 
as  a  crystal  is  formed  in  a  solution.  This  nucleolus  attracts  the  surround- 
ing molecules  of  matter  to  form  the  nucleus,  and  by  a  repetition  of  the 
process  the  substance  and  wall  are  produced. 

This  theory,  once  almost  universally  current,  was  first  disputed  and 
finally  overthrown  by  Eemak  and  Virchow,  whose  researches  established 
the  truth  expressed  in  the  words  "Omnis  cellula  e  cellula.-'^ 

It  will  be  seen  that  this  view  is  in  strict  accordance  with  the  truth 
established  much  earlier  in  Vegetable  Histology  that  every  cell  is  de- 
scended from  some  pre-existing  (mother-)  cell.  This  derivation  of  cells 
from  cells  takes  place  by  (1)  gemmation,  or  {2)  fission  or  divisioji. 

(1.)  Gemmation. — This  method  has  not  been  observed  in  the  human 
body  or  the  higher  animals,  and  therefore  requires  but  a  passing  notice. 
It  consists  essentially  in  the  budding  off  and  separating  of  a  portion  of 
the  parent  cell. 

(2.)  Fission  or  Divisio7i. — As  examples  of  reproduction  by  fission,  we 
may  select  the  ovum,  the  blood  cell,  and  cartilage  cells. 


12 


HAND-BOOK  OF  PHYSIOLOGY. 


In  the  frog's  ovum  (in  which  the  process  can  be  most  readily  ob- 
served) after  fertilization  has  taken  place,  there  is  first  some  amoeboid 
movement,  the  oscillation  gradually  increasing  until  a  permanent  dimple 
appears,  which  gradually  extends  into  a  furrow  running  completely  round 
the  spherical  ovum,  and  deepening  until  the  entire  yelk-mass  is  divided 
into  two  hemispheres  of  protoplasm  each  containing  a  nucleus  (Fig.  4,  h). 
This  process  being  repeated  by  the  formation  of  a  second  furrow  at  right 
angles  to  the  first,  we  have  four  cells  produced  (c):  this  subdivision  is 


Fig.  4.— Diagram  of  an  ovum  (a)  undergoing  segrnentation.  In  (6)  it  has  divided  into  two;  in  (c) 
into  four;  in  (d)  the  process  has  ended  in  the  production  of  the  so-called  "  mulberry  mass."  (Frey.) 

carried  on  till  the  ovum  has  been  diyided  by  segmentation  into  a  mass 
of  cells  (mulberry-mass)  {d)  out  of  which  the  embryo  is  developed. 

Segmentation  is  the  first  step  in  the  development  of  most  animals, 
and  doubtless  takes  place  in  man. 

Multiplication  by  fission  has  been  observed  in  the  colorless  blood-cells 
of  many  animals.  In  some  cases  (Fig.  5),  the  process  has  been  seen  to 
commence  with  the  nucleolus  which  divides  within  the  nucleus.  The 
nucleus  then  elongates,  and  soon  a  well-marked  constriction  occurs,  ren- 
dering it  hour-glass  shaped,  till  finally  it  is  separated  into  two  parts, 
which  gradually  recede  from  each  other:  the  same  process  is  repeated  in 
the  cell-substance,  and  at  length  we  have  two  cells  produced  which  by 


Fig.  5.— Blood-corpuscle  from  a  young  deer  embryo,  multiplying  by  fission.  (Frey.) 

rapid  growth  soon  attain  the  size  of  the  parent  cell  {direct  division).  In 
some  cases  there  is  a  primary  fission  into  three  instead  of  the  usual  two 
cells. 

In  cartilage  (Fig.  6),  a  process  essentially  similar  occurs,  with  the  ex- 
ception that  (as  in  the  ovum)  the  cells  produced  by  fission  remain  in  the 
original  capsule,  and  in  their  turn  undergo  division,  so  that  a  large  num- 
ber of  cells  are  sometimes  observed  within  a  common  envelope.  This 
process  of  fission  within  a  capsule  has  been  by  some  described  as  a  separate 
method,  under  the  title  * 'endogenous  fission,"  but  there  seems  to  bene 
sufiicient  reason  for  drawing  such  a  distinction. 

It  is  important  to  observe  that  fission  is  ofliMi  accomplished  with  great 
rapidity,  the  whole  process  occupying  but  a  few  jninutes,  hence  the  com- 
])arative  rarity  with  Avhich  cells  are  seen  in  the  act  of  dividing. 


STRUCTURAL   BASIS  OF  THE  HUMAN  BODY.  13 

Indirect  cell  division. — In  certain  and  numerous  cases  the  division  of 
cells  does  not  take  place  by  the  simple  constriction  of  their  nuclei  and 
surrounding  protoplasm  into  two  parts  as  above  described  (direct  division), 
but  is  preceded  by  complicated  changes  in  their  nuclei  (karyokinesis). 


Fig.  6.— Diagram  of  a  cartilage  cell  undergoing  fission  within  its  capsule.  The  process  of  divi- 
sion is  represented  as  commencing  in  the  nucleolus,  extending  to  the  nucleus,  and  at  length  involving 
the  body  of  the  cell.  (Frey.) 

These  changes  consist  in  a  gradual  re-arrangement  of  the  intranuclear  net- 
work of  each  nucleus,  until  two  nuclei  are  formed  similar  in  all  respects 
to  the  original  one.  The  nucleus  in  a  resting  condition,  i.e.,  before  any 
changes  preceding  division  occur,  consists  of  a  very  close  meshwork  of 
fibrils,  which  stain  deeply  in  carmine,  imbedded  in  protoplasm,  which 
does  not  possess  this  property,  the  whole  nucleus  being  contained  in  an 
envelope.  The  first  change  consists  of  a  slight  enlargement,  the  disap- 
pearance of  the  envelope,  and  the  increased  definition  and  thickness  of 


Fig.  7.— Karyokinesis.  a,  ordinary  nucleus  of  a  columnar  epithelial  cell;  b,  c,  the  same  nucleus  in 
the  stage  of  convolution;  d,  the  wreath  or  rosette  form;  e,  the  aster  or  single  star;  f,  a  nuclear  spin- 
dle from  the  Descemefs  endothelium  of  the  frog's  cornea:  g,  h,  i,  diaster;  k,  two  daughter  nuclei. 
(Klein.) 

the  nuclear  fibrils,  which  are  also  more  separated  than  they  were  and  stain 
better.  This  is  the  stage  of  convolution  (Fig.  7,  b,  c).  The  next  step  in 
the  process  is  the  arrangement  of  the  fibrils  into  some  definite  figure  by 
an  alternate  looping  in  and  out  around  a  central  space,  by  which  means 


14 


HAISTD-BOOK  OF  PHYSIOLOGY. 


the  rosette  or  wreath  stage  (Fig.  7,  d)  is  reached.  The  loops  of  the  rosette 
next  become  divided  at  the  periphery,  and  their  central  points  become 
more  angular,  so  that  the  fibrils,  divided  into  portions  of  about  equal 
length,  are,  as  it  were,  doubled  at  an  acute  angle,  and  radiate  V-shaped 
from  the  centre,  forming  a  star  (aster)  or  wheel  (Fig.  7,  e),  or  perhaps 
from  two  centres,  in  which  case  a  double  star  (diasterj  results  (Fig.  7,  G, 
H,  and  i).  After  remaining  almost  unchanged  for  some  time,  the 
V-shaped  fibres  being  first  re-arranged  in  the  centre,  side  by  side  (angle 
outward),  tend  to  separate  into  two  bundles,  which  gradually  assume  posi- 
tion at  either  pole.  From  these  groups  of  fibrils  the  two  nuclei  of  the 
new  cells  are  formed  (daughter  nuclei)  (Fig.  7,  k),  and  the  changes  they 
pass  through  before  reaching  the  resting  condition  are  exactly  those 
through  which  the  original  nucleus  (mother  nucleus)  has  gone,  but  in  a 
reverse  order,  viz.,  the  star,  the  rosette,  and  the  convolution.  During 
or  shortly  after  the  formation  of  the  daughter  nuclei  the  cell  itself  be- 
comes constricted,  and  then  divides  in  a  line  about  midway  between  them. 

Functions  of  Cells. — The  functions  of  cells  are  almost  infinitely  varied 
and  make  up  nearly  the  whole  of  Physiology.  They  will  be  inore  appro- 
priately considered  in  the  chapters  treating  of  the  several  organs  and  sys- 
tems of  organs  which  the  cells  compose. 

Decay  and  Death  of  Cells. — There  are  two  chief  ways  in  which  the 
comparatively  brief  existence  of  cells  is  brought  to  an  end.  (1)  Mechani- 
cal abrasion,  (2)  Chemical  transformation. 

1.  The  various  epithelia  furnish  abundant  examples  of  mechanical 
abrasion.  As  it  approaches  the  free  surface  the  cell  becomes  more  and 
more  flattened  and  scaly  in  form  and  more  horny  in  consistence,  till  at 
length  it  is  simply  rubbed  off.  Hence  we  find  epithelial  cells  in  the 
mucus  of  the  mouth,  intestine,  and  genito-urinary  tract. 

2.  In  the  case  of  chemical  transformation  the  cell-contents  undergo  a 
degeneration  which,  though  it  may  be  pathological,  is  very  often  a  normal 
process. 

Thus  we  have  (a.)  fatty  metamorphosis  producing  oil-globules  in  the 
secretion  of  milk,  fatty  degeneration  of  the  muscular  fibres  of  the  uterus 
after  the  birth  of  the  foetus,  and  of  the  cells  of  the  Graafian  follicle  giving 
rise  to  the  ''corpus  luteum.'^    (See  chapter  on  Generation.) 

(b.)  Pigmentary  degeneration  from  deposit  of  pigment,  as  in  the  epi- 
thelium of  the  air-vesicles  of  the  lungs. 

(c.)  Calcareous  degeneration  which  is  common  in  the  cells  of  many 
cartilages. 

Having  thus  reviewed  the  life-history  of  cells  in  general,  we  may  now 
discuss  tlie  leading  van(^tiort  of  form  wliich  they  ])resent. 

In  passing,  it  may  b(^  well  to  i)()int  out  tlie  mw'm  disl i)u-Ho)is  hcfirooi 
anintaJ  (itnl  cvijctaldv  cells. 


STKUCTUKAL    BASIS  OF  THE  HUMAN  BODY. 


15 


It  lias  been  already  mentioned  that  in  animal  cells  an  envelope  or  cell- 
wall  is  by  no  means  always  present.  In  adult  vegetable  cells,  on  the 
other  hand,  a  well-defined  cellulose  wall  is  highly  characteristic;  this,  it 
should  be  observed,  is  non-nitrogenous,  and  tiius  differs  chemically  as 
well  as  structurally  from  the  contained  mass. 

Moreover,  in  vegetable  cells  (Fig.  8,  b),  the  protoplastic  contents  of 
th3  cell  fall  into  two  subdivisions:  (1)  a  continuous  film  which  lines  the 
interior  of  the  cellulose  wall;  and  (2)  a  reticulate  mass  containing  the 


Fig.  8.— (a).  Young  vegetable  cells,  showing  cell-cavity  entirely  filled  with  granular  protoplasm 
enclosing  a  large  oval  nucleus,  with  one  or  more  nucleoli. 

(b.)  Older  cells  from  the  same  plant,  showing  distinct  celltdose-wall  and  vacuolation  of  proto- 
plasm, 

nucleus  and  occupying  the  cell-cavity;  its  interstices  are  filled  with  fluid. 
In  young  vegetable  cells  such  a  distinction  does  not  exist;  a  finely  gran- 
ular protoplasm  occupies  the  whole  cell-cavity  (Fig.  8,  a). 

Another  striking  difference  is  the  frequent  presence  of  a  large  quan- 
tity of  intercellular  substance  in  animal  tissues,  while  in  vegetables  it  is 
comparatively  rare,  the  requisite  consistency  being  given  to  their  tissues 
by  the  tough  cellulose  walls,  often  thickened  by  deposits  of  lignin.  In 
animal  cells  this  end  is  attained  by  the  deposition  of  lime-salts  in  a  matrix 
of  intercellular  substance,  as  in  the  process  of  ossification. 

Forms  of  Cells. — Starting  with  the  spherical  or  spheroidal  (Fig.  9,  d) 
as  the  typical  form  assumed  by  a  free  cell,  we  find  this  altered  to  a  poly- 
hedral shape  when  the  pressure  on  the  cells  in  all  directions  is  nearly  the 
same  (Fig.  9,  l). 

Of  this,  the  primitive  segmentation-cells  may  afford  an  example. 

The  discoid  shape  is  seen  in  blood-cells  (Fig.  9,  c),  and  the  scale-like 


Fig.  9.— Various  forms  of  cells,   a.  Spheroidal,  showing  nucleus  and  nucleolus.   6.  Polyhedral, 
c.  Discoidal  (blood-ceUs).  d.  Scaly  or  squamous  (epithelial  ceUs). 

form  in  superficial  epithelial  cells  (Fig.  9,  Some  cells  have  a  jagged 
outline  (prickle-cells)  (Fig.  13). 

Cylindrical,  conical,  or  prismatic  cells  occur  in  the  deeper  layers  of 
laminated  epithelium,  and  the  simple  cylindrical  epithelium  of  the  intes- 
tine and  many  gland  ducts.    Such  cells  may  taper  off  at  one  or  both 


16 


HAND-BOOK  OF  PHYSIOLOGY. 


ends  into  fine  processes,  in  the  former  case  being  caudate,  in  the  latter 
fusiform  (Fig.  10).  They  may  be  greatly  elongated  so  as  to  become 
fibres.  Ciliated  cells  (Fig.  10,  d)  must  be  noticed  as  a  distinct  variety: 
they  possess,  but  only  on  their  free  surfaces,  hair-like  processes  (cilia). 
These  vary  immensely  in  size,  and  may  even  exceed  in  length  the  cell 
itself.    Finally  we  have  the  branched  or  stellate  cells,  of  which  the  large 


Fig.  10.— Various  forms  of  cells,  a.  Cylindrical  or  columnar,  h.  Caudate,  c.  Fusiform,  d.  Cilia- 
ted (from  trachea),   e.  Branched,  stellate. 


nerve-cells  of  the  spinal  cord,  and  the  connective  tissue  corpuscle  are 
typical  examples  (Fig.  10,  e).  In  these  cells  the  primitive  branches  by 
secondary  branching  may  give  rise  to  an  intricate  network  of  processes. 

Classification  of  Cells. — Cells  may  be  classified  in  many  ways. 
According  to: — 

(a.)  Form  :  They  may  be  classified  into  spheroidal  or  polyhedral,  dis- 
coidal,  flat  or  scaly,  cylindrical,  caudate,  fusiform,  ciliated  and  stellate. 

(b.)  Situation: — we  may  divide  them  into  blood  cells,  gland  cells, 
connective  tissue  cells,  etc. 

(c.)  Contents: — fat  and  pigment  cells  and  the  like. 

(d.)  Function: — secreting,  protective,  contractile,  etc. 

(e.)  Origin : — hypoblastic,  mesoblastic,  and  epiblastic  cells.  (See 
chapter  on  Generation.) 

It  remains  only  to  consider  the  various  ways  in  which  cells  arc  con- 
nected together  to  form  tissues,  and  the  transformations  by  which  inter- 
cellular substance,  fibres  and  tubules  are  produced. 

Modes  of  connection. — Cells  are  connected: — 

(1)  By  a  cementing  intercellular  substance.  This  is  probably  always 
present  as  a  transparent,  colorless,  viscid,  albuminous  substance,  even 
between  the  closely  apposed  cells  of  cylindrical  epithelium,  while  in  the 
case  of  cartihigo  it  forms  the  main  bulk  of  the  tissue,  and  the  cells  only 
appear  as  imbedded  in,  not  as  cemented  by,  the  intercellular  substance. 

This  intercellular  substance  may  be  either  homogeneous  or  fibrillated. 

In  many  ceases  (cj/.       ci)vm\\)  it  can  l)c  shown  to  contain  a  number 


STRUCTURAL  BASIS  OF  THE  HUMAN  BODY. 


17 


of  irregular  branched  cavities,  which  communicate  with  each  other,  and 
in  which  the  branched  cells  lie:  through  these  branching  spaces  nutritive 
fluids  can  find  their  v/ay  into  the  very  remotest  parts  of  a  non-vascular 
tissue. 

As  a  special  variety  of  intercellular  substance  must  be  mentioned  the 
basement  membrane  {memhrana  propria)  which  is  found  at  the  base  of 
the  epithelial  cells  in  most  mucous  membranes,  and  especially  as  an  in- 
vesting tunic  of  gland  follicles  which  determines  their  shape,  and  which 
may  persist  as  a  hyaline  saccule  after  the  gland -cells  have  all  been  dis- 
charged. 

(2)  By  anastomosis  of  their  processes. 

This  is  the  usual  way  in  which  stellate  cells,  e.g.,  of  the  cornea,  are 
united:  the  individuality  of  each  cell  is  thus  to  a  great  extent  lost  by  its 
connection  with  its  neighbors  to  form  a  reticulum :  as  an  example  of  a  net- 
work so  produced,  Ave  may  cite  the  stroma  of  lymphatic  glands. 

Sometimes  the  branched  processes  breaking  up  into  a  maze  of  minute 
fibrils,  adjoining  cells  are  connected  by  an  intermediate,  reticulum:  this 
is  the  case  in  the  nerve-cells  of  the  spinal  cord. 

Besides  the  Cell,  which  may  be  termed  the  primary  tissue-element, 
there  are  materials  which  may  be  termed  secondary  or  derived  tissue- 
elements.    Such  are  Intercellular  substance.  Fibres  and  Tubules. 

Intercellular  substance  is  probably  in  all  cases  directly  derived  from 
the  cells  themselves.  In  some  cases  {e.g.  cartilage),  by  the  use  of  re- 
agents the  cementing  intercellular  substance  is,  as  it  were,  analyzed  into 
various  masses,  each  arranged  in  concentric  layers  around  a  cell  or  group 
of  cells,  from  which  it  was  probably  derived  (Fig.  6). 

Fibres.  — In  the  case  of  the  crystalline  lens,  and  of  muscle  both  stri- 
ated and  non-striated,  each  fibre  is  simply  a  metamorphosed  cell:  in  the 
case  of  striped  fibre  the  elongation  being  accompanied  by  a  multiplication 
of  the  nuclei. 

The  various  fibres  and  fibrillse  of  connective  tissue  result  from  a  grad- 
ual transformation  of  an  originally  homogeneous  intercellular  substance. 
Fibres  thus  formed  may  undergo  great  chemical  as  well  as  physical  trans- 
formation: this  is  notably  the  case  with  yellow  elastic  tissue,  in  which 
the  sharply  defined  elastic  fibres,  possessing  great  power  of  resistance  to 
re-agents,  contrast  strikingly  with  the  homogeneous  matter  from  which 
they  are  derived. 

Tubules  which  were  originally  supposed  to  consist  of  structureless, 
membrane,  have  now  been  proved  to  be  composed  of  flat,  thin  cells, 
cohering  along  their  edges.    (See  Capillaries.) 

With  these  simple  materials  the  various  parts  of  the  body  are  built  up; 
the  more  elementary  tissues  being,  so  to  speak,  first  compounded  of 
YoL.  I.— 3. 


18 


HAND-BOOK  OF  PHYSIOLOaY. 


them;  while  these  again  are  variously  mixed  and  interwoven  to  form 
more  intricate  combinations. 

Thus  are  constructed  epithelium  and  its  modifications,  connective 
tissue,  fat,  cartilage,  bone,  the  fibres  of  muscle  and  nerve,  etc. ;  and  these, 
again,  with  the  more  simple  structures  before  mentioned,  are  used  as 
materials  wherewith  to  form  arteries,  veins,  and  lymphatics,  secret?  ug 
and  vascular  glands,  lungs,  heart,  liver,  and  other  parts  of  the  body. 


CHAPTEK  III. 


STRUCTURE  OF  THE  ELEMENTARY  TISSUES. 

Il^"  this  chapter  the  leading  characters  and  chief  modifications  of  two 
great  groups  of  tissues — the  Epithelial  and  Connective — will  be  briefly  de- 
scribed; while  the  Nervous  and  Muscular,  together  with  several  other 
more  highly  specialized  tissues,  will  be  appropriately  considered  in  the 
chapters  treating  of  their  physiology. 

Epithelium. 

Epithelium  is  composed  of  cells  of  various  shapes  held  together  by  a 
small  quantity  of  cementing  intercellular  substance. 

Epithelium  clothes  the  whole  exterior  surface  of  the  body,  forming 
the  epidermis  with  its  appendages — nails  and  hairs;  becoming  continuous 
at  the  chief  orifices  of  the  body — nose,  mouth,  anus,  and  urethra — with 
the  epithelium  which  lines  the  whole  length  of  the  alimentary  and  genito- 
urinary tracts,  together  with  the  ducts  of  their  various  glands.  Epi- 
^  thelium  also  lines  the  cavities  of  the  brain,  and  the  central  canal  of  the 
spinal  cord,  the  serous  and  synovial  membranes,  and  the  interior  of  all 
blood-vessels  and  lymphatics. 

The  cells  composing  it  may  be  arranged  in  either  one  or  more  layers, 
and  thus  it  may  be  subdivided  into  {a)  Simple  and  {h)  Stratified  or 
laminated  Epithelium.  A  simple  epithelium,  for  example,  lines  the 
whole  intestinal  mucous  membrane  from  the  stomach  to  the  anus:  the 
epidermis  on  the  other  hand  is  laminated  throughout  its  entire  extent. 

Epithelial  cells  possess  an  intracellular  and  an  intranuclear  network 
(p.  10).  They  are  held  together  by  a  clear,  albuminous,  cement  sub- 
stance. The  viscid  semi-fluid  consistency  both  of  cells  and  intercellular 
substance  permits  such  changes  of  shape  and  arrangement  in  the  individ- 
ual cells  as  are  necessary  if  the  epithelium  is  to  maintain  its  integrity  in 
organs  the  area  of  whose  free  surface  is  so  constantly  changing,  as  the 
stomach,  lungs,  etc.  Thus,  if  there  be  but  a  single  layer  of  cells,  as  in 
the  epithelium  lining  the  air  vesicles  of  the  lungs,  the  stretching  of  this 
membrane  causes  such  a  thinning  out  of  the  cells  that  they  change  their 
shape  from  spheroidal  or  short  columnar,  to  squamous,  and  vice  versa, 
when  the  membrane  shrinks. 


20 


HAND-BOOK  OF  PHYSIOLOGY. 


Classification  of  Epithelial  Cells. 

Epithelial  cells  may  be  conveniently  classified  as: 

1.  Sgimmous,  scaly,  pavement,  or  tessellated. 

2.  Spheroidal,  glandular,  or  polyliedral. 

3.  Columnar,  cylindrical,  conical,  or  gohlet-sliaped, 

4.  Ciliated.  '  ' 

5.  Transitional. 

Altliougli,  for  convenience,  epithelial  cells  are  thus  classified,  yet  the 
first  three  forms  of  cells  are  sometimes  met  with  at  different  depths  in 


Fig.  11.— Vertical  section  of  Rabbit's  cornea,  a.  Anterior  epithelium,  shoeing  the  different 
shapes  of  the  ceUs  at  vai-ious  depths  from  the  free  surface,  b.  Portion  of  the  substance  of  cornea. 
(Klein.) 

che  same  membrane.  As  an  example  of  snch  a  laminated  epithelium 
showing  these  different  cell-forms  at  various  depths,  we  may  select  the 
anterior  epithelium  of  the  cornea  (Fig.  11). 

1.  Squamous  Epithelium  (Fig.  12). — Arranged  (a)  in  several  super- 
posed layers  {stratified  or  laminated),  this  form  of  epithelium  covers  {a) 
the  skin,  where  it  is  called  the  Epidermis,  and  lines  {h)  the  mouth, 

pharynx,  and  oesophagus,  {c)  the  conjunc- 
tiva, {d)  the  vagina,  and  entrance  of  the 
urethra  in  both  sexes;  while,  as  (b)  a  single 
layer,  the  same  kind  of  epithelium  forms 
{a)  the  pigmentary  layer  of  the  retina, 
and  lines  {h)  the  interior  of  the  serous  and 
synovial  sacs,  and  (r)  of  the  heart,  blood 
J^?  tl.1;l.SrTtreS^^^^^  and  lymph-vessels  (Eiulotlielium).    It  con- 

^^^""'^•^  sists  of  cells,  which  are  llattened  and  scaly, 

"with  an  irregular  outline:  and,  when  laminated,  may  form  a  dense  horny 
investment,  as  on  parts  of  the  palms  of  the  hands  and  soles  of  the  feet. 
Tlie  nucleus  is  often  not  apparent.  Tlie  really  cellular  nature  of  ovon 
tlie  dry  and  shriveled  scales  (last  off  from  the  surface  of  the  epidermis, 
can  be  proved  by  the  application  of  caustic  potash,  which  causes  them 
ra])i(1ly  to  s\v(>ll  and  assume  th(Mr  original  form. 


STRUCTURE  OF  THE  ELEMENTARY  TISSUES.  21 

Squamous  cells  are  generally  united  by  an  intercellular  substance;  but 
in  many  of  the  deeper  layers  of  epithelium  in  the  mouth  and  skin,  the 
outline  of  the  cells  is  very  irregular. 

Such  cells  (Fig.  13)  are  termed  * 'ridge  and  furrow/'  ''cogged"  or 
"prickle"  cells.  These  "prickles"  are  prolongations  of  the  intra-cellular 
network  which  run  across  from  cell  to  cell,  thus  joining  them  together, 
the  interstices  being  filled  by,  the  transparent  intercellular  cement  sub- 
stance. When  this  increases  in  quantity  in  inflammation,  the  cells  are 
pushed  further  apart  and  the  connecting  fibrils  or  "prickles"  elongated, 
and  therefore  more  clearly  visible. 

Squamous  epithelium,  e.g.  the  pigment  cells  of  the  retina,  may  have 
a  deposit  of  pigment  in  the  cell-substance.  This  pigment  consists  of 
minute  molecules  of  melanin,  imbedded  in  the  cell-substance  and  almost 
concealing  the  nucleus,  which  is  itself  transparent  (Fig.  14). 

In  white  rabbits  and  other  albino  animals,  in  which  the  pigment  of 


Fig.  13.  Fig.  14. 


Fig.  13.— Jagged  cells  of  the  middle  layers  of  pavement  epithelium,  from  a  vertical  section  of 
the  gum  of  a  new-born  infant.  (Klein.) 

Fig.  14.— Pigment  cells  from  the  retina.  A,  cells  stjU  cohering,  seen  on  their  surface;  a,  nucleus 
indistinctly  seen.  In  the  other  ceUs  the  nucleus  is  concealed  by  the  pigment  granules.  B,  two  cells 
seen  in  profile;  a,  the  outer  or  posterior  part  containing  scarcely  any  pigment,    x  370.  (Henle.) 

the  eye  is  absent,  this  layer  is  found  to  consist  of  colorless  pavement 
epithelial  cells. 

Endothelium. — The  squamous  epithelium  lining  the  serous  mem- 
branes, and  the  interior  of  blood-vessels,  presents  so  many  special  features 
as  to  demand  a  special  description;  it  is  called  by  a  distinct  name — En- 
dothelium. 

The  main  points  of  distinction  above  alluded  to  are,  1.  the  very  flat- 
tened form  of  these  cells;  2.  their  constant  occurrence  in  only  a  single 
layer;  3.  the  fact  that  they  are  developed  from  the  "mesoblast,"  while 
all  other  epithelial  cells  are  derived  from  the  "epiblast,"  or  "hjrpoblast;^' 
4.  they  line  closed  ■  cavities  not  communicating  with  the  exterior  of  the 
body.  Endothelial  cells  form  an  important  and  well-defined  subdivision 
of  squamous  epithelial  cells,  which  has  been  especially  studied  during 
the  last  few  years.  Their  examination  has  been  much  facilitated  by  the 
adoption  of  the  method  of  staining  serous  membranes  with  silver  nitrate. 


22 


HAND-BOOK  OF  PHYSIOLOGY. 


When  a  small  portion  of  a  perfectly  fresh  serous  membrane,  as  the 
mesentery  or  omentum  (Fig.  15),  is  immersed  for  a  few  minutes  in  a 
quarter  per  cent,  solution  of  this  re-agent,  washed  with  water  and  exposed 
to  the  action  of  light,  the  silver  oxide  is  precipitated  along  the  bounda- 


FiG.  15. — Part  of  the  omentum  of  a  cat,  stained  in  silver  nitrate,  X  100.  The  tissue  forms  a  '•'•fenes- 
trated TJiemftrane,"  that  is  to  say,  one  which  is  studded  with  holes  or  windows.  In  the  figiu*e  these 
are  of  various  shapes  and  sizes,  leaving  trabeculae,  the  basis  of  which  is  fibrous  tissue.  The  trabecu- 
Ise  are  of  various  sizes,  and  are  covered  with  endothelial  cells,  the  nuclei  of  which  have  been  made 
evident  by  staining  with  hsematoxylin  after  the  silver  nitrate  has  outUned  the  ceUs  by  staining  the 
intercellular  substance.   (V.  D.  Harris.) 

ries  of  the  cells,  and  the  whole  surface  is  found  to  be  marked  out  with 
exquisite  delicacy,  by  fine  dark  lines,  into  a  number  of  polygonal  spaces 
(endothelial  cells)  (Figs.  15  and  16). 

Endothelium  lines,  as  before  mentioned,  all  the  serous  cavities  of  the 


Fig.  16.— Abdominal  surface  of  centrum  tendineum  of  dlaphrapm  of  rabbit,  showine  the  general 

polygonal  shape  of  the  endothelial  cells;  each  is  nucleated.    (Klein.)   X  300. 

body,  including  tlio  anterior  chamber  of  the  eye,  also  the  synovial  mem- 
branes of  joints,  and  the  interior  of  the  lieart  and  of  all  blood-vessels  and 
lymphatics.     It  forms  also  a  delic^ate  investing  sheath  for  nerve-fibres 


STRUCTURE  OF  THE  ELEMENTARY  TISSUES. 


23 


and  peripheral  ganglion-cells.  The  cells  are  scaly  in  form,  and  irregular 
in  outline;  those  lining  the  interior  of  blood-vessels  and  lymphatics  hav- 
ing a  spindle-shape  with  a  very  wavy  outline.  They  enclose  a  clear,  oval 
nucleus,  which,  when  the  cell  is  viewed  in  profile,  is  seen  to  project  from 
its  surface. 

Endothelial  cells  may  be  ciliated,  e.g.,  those  in  the  mesentery  of 
frogs,  especially  about  the  breeding  season. 

Besides  the  ordinary  endothelial  cells  above  described,  there  are  found 
on  the  omentum  and  parts  of  the  pleura  of  many  animals,  little  bud-like 
processes  or  nodules,  consisting  of  small  polyhedral  granular  cells,  round- 
ed on  their  free  surface,  which  multiply  very  rapidly  by  division  (Fig. 
17).    These  constitute  what  is  known  as  ''germinating  endothelium." 


Fig.  17. — Silver-stained  preparation  of  great  omentiuii  of  dog,  which  shows,  amongst  the  flat 
endothehum  of  the  surface,  small  and  large  groups  of  germinating  endothehum,  between  which 
numbers  of  stomata  are  to  be  seen.   (Klein.)  x  300. 

The  process  of  germination  doubtless  goes  on  in  health,  and  the  small  cells 
which  are  thrown  off  in  succession  are  carried  into  the  lymphatics,  and 
contribute  to  the  number  of  the  lymph  corpuscles.  The  buds  may  be 
enormously  increased  both  in  number  and  size  in  certain  diseased  condi- 
tions. 

On  those  portions  of  the  peritoneum  and  other  serous  membranes 
where  lymphatics  abound,  there  are  numerous  small  orifices — stomata — 
(Fig.  18)  between  the  endothelial  cells:  these  are  really  the  open  mouths 
of  lymphatic  vessels,  and  through  them  lymph-corpuscles,  and  the  serous 
fluid  from  the  serous  cavity,  pass  into  the  lymphatic  system. 

2.  Spheroidal  epithelial  cells  are  the  active  secreting  agents  in  most 


24 


HAND-BOOK  OF  PHYSIOLOGY. 


secreting  glands,  and  hence  are  often  termed  glandular;  they  are  gener- 
ally more  or  less  rounded  in  outline:  often  polygonal  from  mutual  pres- 
sure. 


Fig.  18. — Peritoneal  surface  of  septiim  cisternse  lymphaticae  magnae  of  frog.  The  stomata,  some 
of  which  are  open^  som6  collapsed,  are  surrounded  by  germinating  endotheUum.   (Klein.)   x  160. 

Excellent  examples  are  to  be  found  in  the  liver,  the  secreting  tubes  of 
the  kidney,  and  in  the  salivary  and  peptic  glands  (Fig.  19). 

3.  Columnar  epithelium  (Fig.  20,  A  and  b)  lines  (a.)  the  mucous  mem- 
brane of  the  stomach  and  intestines,  from  the  cardiac  orifice  of  the  stomach 
to  the  anus,  and  (b.)  wholly  or  in  part  the  ducts  of  the  glands  opening  on 


A 


Fig.  19.— Glandular  epithelium.   A,  small  lobule  of  a  mucous  gland  of  the  tongue,  showing  nu- 
cleated glandular  spheroidal  cells.   B,  Liver  cells.    X  200.   (V.  D.  HaiTis.) 

its  free  surface;  also  (c.)  many  gland-ducts  in  other  regions  of  the  body, 
e.f/.j  mammary,  salivary,  etc.;  (d.)  the  cells  which  form  tlio  deeper  layers 
of  the  epithelial  lining  of  tlie  tracliea  are  approximately  columnar. 

It  consists  of  cells  which  are  cylindrical  or  prismatic  in  form,  and  con- 
tain a  largo  oval  nucleus.  When  evenly  packed  side  by  side  as  a  single 
layer,  the  cells  are  uniformly  columnar;  but  when  occurring  in  several 
layers  as  in  the  deeper  strata  of  the  epithelial  lining  of  the  trachea,  their 


STKUCTURE  OF  THE  ELEMENTARY  TISSUES. 


25 


shape  is  very  variable,  and  often  departs  very  widely  from  the  typical 
columnar  form. 

GoUet-cells. — Many  cylindrical  epithelial  cells  undergo  a  curious  trans- 
formation, and  from  the  alteration  in  their  shape  are  termed 
(Fig.  20,  A,  c,  and  b). 

These  are  never  seen  in  a  perfectly  fresh  specimen 
specimen  be  watched  for  some  time,  little  knobs  are  seen 


Fig.  20.— a.  Vertical  section  of  a  villus  of  the  small  intestine  of  a  cat.  a.  Striated  basilar  border 
of  the  epithelium,  h.  Columnar  epithelium,  c.  Goblet  cells,  d.  Central  lymph-vessel,  e.  Smooth 
muscular  fibres.  /.  Adenoid  stroma  of  the  villus  in  which  lymph  corpuscles  lie.  B.  Goblet  cells. 
(Klein.) 

ing  on  the  free  surface  of  the  epithelium,  and  are  finally  detached;  these 
consist  of  the  cell-cont3nts  which  are  discharged  by  the  open  mouth  of 
the  goblet,  leaving  the  nucleus  surrounded  by  the  remains  of  the  proto- 
plasm in  its  narrow  stem. 

Some  regard  this  transformation  as  a  normal  process  which  is  continu- 
ally going  on  during  life,  the  discharged  cell-contents  contributing  to  form 
mucus,  the  cells  being  supposed  in  many  cases  to  recover  their  original 
shape. 

The  columnar  epithelial  cells  of  the  alimentary  canal  possess  a  struc- 
tureless layer  on  their  free  surface:  such  a  layer,  appearing  striated  when 
viewed  in  section,  is  termed  the  '^striated  basilar  border"  (Fig.  20,  a,  ci), 

4.  Ciliated  cells  are  generally  cylindrical  (Fig.  21,  b),  but  may  be 
spheroidal  or  even  almost  squamous  in  shape  (Fig.  21,  a). 

This  form  of  epithelium  lines  (a.)  the  whole  of  the  respiratory  tract 
from  the  larynx  to  the  finest  subdivisions  of  the  bronchi,  also  the  lower 
parts  of  the  nasal  passages,  and  some  portions  of  the  generative  apparatus 
— in  the  male  (b.)  lining  the  "vasa  efferentia"  of  the  testicle,  and  their 
prolongations  as  far  as  the  lower  end  of  the  epididymis;  in  the  female 
(c.)  commencing  about  the  middle  of  the  neck  of  the  uterus,  and  extend- 
ing throughout  the  uterus  and  Fallopian  tubes  to  their  fimbriated  ex- 
tremities, and  even  for  a  short  distance  on  the  peritoneal  surface  of  the 
latter,    (d.)  The  ventricles  of  the  brain  and  the  central  canal  of  the 


26 


HAND-BOOK  OF  PHYSIOLOGY. 


spinal  cord  are  clothed  with  ciliated  epithelium  in  the  child,  but  in  the 
adult  it  is  limited  to  the  central  canal  of  the  cord. 

The  Cilia,  or  fine  hair-like  processes  which  give  the  name  to  this  va- 
riety of  epithelium,  vary  a  good  deal  in  size  in  different  classes  of  animals, 
being  very  much  smaller  in  the  higher  than  among  the  lower  orders,  in 
which  they  sometimes  exceed  in  length  the  cell  itself. 

The  number  of  cilia  on  any  one  cell  ranges  from  ten  to  thirty,  and 
those  attached  to  the  same  cell  are  often  of  different  lengths.  When  liv- 
ing ciliated  epithelium,  e.g.,  the  gill  of  a  mussel,  is  examined  under  the 
microscope,  the  cilia  are  seen  to  be  in  constant  rapid  motion;  each  cilium 
being  fixed  at  one  end,  and  swinging  or  lashing  to  and  fro.  The  gen- 
eral impression  given  to  the  eye  of  the  observer  is  very  similar  to  that  pro- 
duced by  waves  in  a  field  of  corn,  or  swiftly  running  and  rippling  water. 


B 


Fig.  21.— a.  Spheroidal  ciliated  cells  from  the  mouth  of  the  frog,  x  300  diameters.  (Sharpey.) 
B.  a.  Ciliated  colmnnar  epithehimi  lining  a  bronchus,    h.  Branched  connective-tissue  corpuscles. 

(Klein  and  Noble  Smith.) 

and  the  result  of  their  movement  is  to  produce  a  continuous  current  in 
a  definite  direction,  and  this  direction  is  invariably  the  same  on  the  same 
surface,  being  always,  in  the  case  of  a  cavity,  toward  its  external  orifice. 

5.  Transitional  Einthelium. — This  term  has  been  applied  to  cells 
which  are  neither  arranged  in  a  single  layer,  as  is  the  case  with  simple 
epithelium,  nor  yet  in  many  superimposed  strata  as  in  laminated;  in  other 
words,  the  term  is  employed  when  epithelial  cells  are  found  in  two,  three, 
or  four  superimposed  layers.  The  upper  layer  may  be  either  columnar, 
ciliated,  or  squamous.  When  the  upper  layer  is  columnar  or  ciliated,  the 
second  layer  consists  of  smaller  cells  fitted  into  the  inequalities  of  the 
cells  above  them,  as  in  the  trachea  (Fig.  21,  b).  The  epithelium  which 
is  met  with  lining  the  urinary  bladder  and  ureters  is,  however,  the 
sitional  par  cxcelleiice.  In  this  variety  there  are  two  or  three  layers  of 
cells,  the  upper  being  more  or  less  flattened  according  to  the  full  or  col- 
lapsed condition  of  the  organ,  their  under  surface  being  marked  with 
one  or  more  dejiressions,  into  which  the  heads  of  the  next  layer  of  club- 
shaped  cells  fit.  Between  the  lower  and  narrower  ])arts  of  the  second  row 
of  cells,  are  fixed  the  irregular  cells  which  constitute  the  third  row,  and 
in  like  manner  sometimes  a  fourth  row  (Fig.  22).  It  can  be  easily  under- 
stood, therefore,  that  if  a  scraping  of  the  mucous  niembnino  of  the  blad- 


STRUCTURE  OF  THE  ELEMENTARY  TISSUES. 


27 


der  be  teazed,  and  examined  under  the  microscope,  cells  of  a  great  variety 
of  forms  may  be  made  out  (Fig.  23).  Each  cell  contains  a  large  nucleus, 
and  the  larger  and  superficial  cells  often  possess  two. 

Special  Epithelium  in  Organs  of  Special  Sense. — In  addition 
to  the  above  kinds  of  epithelium,  certain  highly  specialized  forms  of  epi- 
thelial cells  are  found  in  the  organs  of  smell,  sight,  and  hearing,  viz.. 


Fig.  22.— Epithelium  of  the  bladder;  a,  one  of  the  cells  of  the  first  row;  6,  a  cell  of  the  second 
row;  c,  cells  in  situ,  of  first,  second,  and  deepest  layers.  (Obersteiner.) 

Fig.  23. — Transitional  epithelial  cells  from  a  scraping  of  the  mucous  membrane  of  the  bladder  of 
the  rabbit.   (V.  D.  Harris.) 

olfactory  cells,  retinal  rods  and  cones,  auditory  cells;  they  will  be  de- 
scribed in  the  chapters  which  deal  with  their  functions. 

Functions  of  Epithelium. — According  to  function,  epithelial  cells 
may  be  classified  as: — 

(1.)  Protective,  e.g.,  in  the  skin,  mouth,  blood-vessels,  etc. 
(2.)  Protective  a7id  inoving — ciliated  epithelium. 
(3.)  Secreting — glandular  epithelium;  or.  Secreting  formed  elements 
— epithelium  of  testicle  secreting  spermatozoa. 

(4.)  Protective  and  secreting,  e.g.,  epithelium  of  intestine. 

(5.)  Sensorial,  e.g.,  olfactory  cells,  rods  and  cones  of  retina,  organ  of 


Epithelium  forms  a  continuous  smooth  investment  over  the  whole 
body,  being  thickened  into  a  hard,  horny  tissue  at  the  points  most  ex- 
posed to  pressure,  and  developing  various  appendages,  such  as  hairs  and 
nails,  whose  structure  and  functions  will  be  considered  in  a  future  chapter. 
Epithelium  lines  also  the  sensorial  surfaces  of  the  eye,  ear,  nose,  and 
mouth,  and  thus  serves  as  the  medium  through  which  all  impressions 
from  the  external  world — touch,  smell,  taste,  sight,  hearing — reach  the 
delicate  nerve-endings,  whence  they  are  conveyed  to  the  brain. 

The  ciliated  epithelium  which  lines  the  air-passages  serves  not  only 
as  a  protective  investment,  but  also  by  the  movements  of  its  cilia  is  en- 
abled to  propel  fluids  and  minute  particles  of  solid  matter  so  as  to  aid 
their  expulsion  from  the  body.    In  the  case  of  the  Fallopian  tube,  this 


Fig.  22. 


Fig.  23. 


Corti. 


28 


HAND-BOOK  OF  PHYSIOLOGY. 


agency  assists  the  progress  of  the  ovum  toward  the  cavity  of  the  uterus. 
Of  the  purposes  served  by  cilia  in  the  ventricles  of  the  brain,  nothing  is 
known.  (For  an  account  of  the  nature  and  conditions  of  ciliary  motion, 
see  chapter  on  Motion.) 

The  epithelium  of  the  various  glands,  and  of  the  whole  intestinal 
tract,  has  the  power  of  secretion,  i.e.,  of  chemically  transforming  certain 
materials  of  the  blood;  in  the  case  of  mucus  and  saliva  this  has  been 
proved  to  involve  the  transformation  of  the  epithelial  cells  themselves; 
the  cell-substance  of  the  epithelial  cells  of  the  intestine  being  discharged 
by  the  rupture  of  their  envelopes,  as  mucus. 

Epithelium  is  likewise  concerned  in  the  processes  of  transudation,  dif- 
fusion, and  absorption. 

It  is  constantly  being  shed  at  the  free  surface,  and  reproduced  in  the 
deeper  layers.  The  various  stages  of  its  growth  and  development  can  be 
well  seen  in  a  section  of  any  laminated  epithelium,  such  as  the  epidermis. 


The  Coi^nective  Tissues. 

This  group  of  tissues  forms  the  Skeleton  with  its  various  connections 
— ^bones,  cartilages,  and  ligaments — and  also  affords  a  supporting  frame- 
work and  investmxcnt  to  various  organs  composed  of  nervous,  muscular, 
and  glandular  tissue.  Its  chief  function  is  the  mechancial  one  of  sup- 
port, and  for  this  purpose  it  is  so  intimately  interwoven  with  nearly  all 
the  textures  of  the  body,  that  if  all  other  tissues  could  be  removed,  and 
the  connective  tissues  left,  we  should  have  a  wonderfully  exact  model  of 
almost  every  organ  and  tissue  in  the  body,  correct  even  to  the  smallest 
minutiffi  of  structure. 

Classification  of  Connective  Tissues. — The  chief  varieties  of 
connective  tissues  may  be  thus  classified: — 

I.  The  Eibrous  Coki^ectiye  Tissues. 

A. — Chief  Forms.  B. — Special  Varieties, 

a.  Areolar.  a.  Gelatinous. 

I.  White  fibrous.  I.  Adenoid  or  Retiform. 

c.  Elastic.  c.  Neuroglia. 

d.  Adipose. 

II.  Cartilage. 
III.  Bone. 


All  of  the  varieties  of  connective  tissue  are  made  up  of  two  parts, 
namely,  cells  and  intercellular  substance. 
Cells. — The  cells  are  of  two  kinds. 

(a.)  Fixed. — These  are  cells  of  a  flattened  sluipe,  with  branched  pro- 


STRUCTURE  OF  THE  ^ELEMENTARY  TISSUES. 


29 


cesses,  which  are  often  united  together  to  form  a  network:  they  can  be 
most  readily  observed  in  the  cornea  in  which  they  are  arranged,  layer 
above  layer,  parallel  to  the  free  surface.  They  lie  in  spaces,  in  the  inter- 
cellular or  ground  substance,  which  are  of  the  same  shape  as  the  cells 
they  contain  but  rather  larger,  and  which  form  by  anastomosis  a  system 
of  branching  canals  freely  communicating  (Fig.  24). 


Fig.  24.— Horizontal  preparation  of  cornea  of  frog,  stained  in  gold  chloride;  showing  the  network 
of  branched  cornea  corpuscles.   The  ground-substance  is  completely  colorless.    X  400.  (Klein.) 

To  this  class. of  cells  belong  the  flattened  tendon  corpuscles  which  are 
arranged  in  long  lines  or  rows  parallel  to  the  fibres  (Fig.  29). 

These  branched  cells,  in  certain  situations,  contain  a  number  of  pig- 
ment-granules, giving  them  a  dark  appearance:  they  form  one  variety  of 
pigment-cells.  Branched  pigment-cells  of  this  kind  are  found  in  the 
outer  layers  of  the  choroid  (Fig.  25).  In  many 
lower  animals,  such  as  the  frog,  they  are  found 
widely  distributed,  not  only  in  the  skin,  but  also  in 
many  internal  parts,  e.g.,  the  mesentery  and  sheaths 
of  blood-vessels.  In  the  web  of  the  frog^s  foot  such 
pigment-cells  may  be  seen,  with  pigment  evenly 
distributed  through  the  body  of  the  cell  and  its 
processes;  but  under  the  action  of  light,  electricity, 
and  other  stimuli,  the  pigment-granules  become 
massed  in  the  body  of  the  cell,  leaving  the  processes 
quite  hyaline;  if  the  stimulus  be  removed,  they 
will  gradually  be  distributed  again  all  over  the  pro- 
cesses. Thus  the  skin  in  the  frog  is  sometimes 
uniformly  dusky,  and  sometimes  quite  light-col- 
ored, with  isolated  dark  spots.  In  the  choroid  and  retina  the  pigment- 
cells  absorb  light. 

(5.)  Amcehoid  cells,  of  an  approximately  spherical  shape:  they  have  a 
great  general  resemblance  to  colorless  blood  corpuscles  (Fig.  2),  with 


Fig.  25.— Ramified  pig- 
ment-ceUs  from  the  tissue 
of  the  choroid  coat  of  the 
eye.  X  350.  a,  cell  with 
pigment;  6,  colorless  fusi- 
form cells.  (KoUiker.) 


30 


HAND-BOOK  OF  PHYSIOLOGY. 


which  some  of  them  are  probably  identical.  They  consist  of  finely  gran- 
ular nucleated  protoplasm,  and  have  the  property,  not  only  of  changing 
their  form,  but  also  of  moving  about,  whence  they  are  termed  migra- 
tory. They  are  readily  distinguished  from  the  branched  connective-tissue 
corpuscles  by  their  free  condition,  and  the  absence  of  processes.  Some 
are  much  larger  than  others,  and  are  found  especially  in  the  sublingual 
gland  of  the  dog  and  guinea  pig  and  in  the  mucous  membrane  of  the 
intestine.  A  second  variety  of  these  cells  called  i^lasma  cells  (Waldeyer) 
are  larger  than  the  amoeboid  cells,  apparently  granular,  less  active  in  their 
movements.  They  are  chiefly  to  be  found  in  the  inter-muscular  septa, 
in  the  mucous  and  submucous  coats  of  the  intestine,  in  lymphatic  glands, 
and  in  the  omentum. 

Intercellular  Substance. — This  may  be  fibrillar,  as  in  the  fibrous 
tissues  and  certain  varieties  of  cartilage;  or  homogeneous,  as  in  hyaline 
cartilage. 


Fig.  26.  Fig.  27. 

Fig.  26.— Flat,  pigmented,  branched,  connective-tissue  cells  from  the  sheath  of  a  large  blood-ves- 
sel of  frog's  mesentery:  the  pigment  is  not  distributed  uniformly  through  the  substance  of  the  larger 
cell,  consequently  some  parts  of  the  cell  look  blacker  than  others  (uncontracted  state).  In  the  two 
smaller  cells  most  of  the  pigment  is  withdrawn  into  the  cell-body,  so  that  they  appear  smaller,  black- 
er, and  less  branched.    X  350.    (KUein  and  Noble  Smith.) 

Fig.  27.— Fibrous  tissue  of  cornea,  showing  bundles  of  fibres  with  a  few  scattered  fusiform  cells 
lying  in  the  inter-fascicular  spaces,    x  400.   (Klein  and  Noble  Smith.) 

The  fibres  composing  the  former  are  of  two  kinds — (a.)  White  fibres. 
(J.)  Yellow  elastic  fibres. 

(«.)  Wliite  Fibres. — These  are  arranged  parallel  to  each  other  in  wavy 
bundles  of  various  sizes:  such  bundles  may  either  have  a  parallel  arrange- 
ment (Fig.  27),  or  may  produce  quite  a  felted  texture  by  their  interlace- 
ment. The  individual  fibres  composing  these  fasciculi  are  homogeneous, 
unbranched,  and  of  the  same  diameter  throughout.  They  can  readily 
be  isolated  by  macerating  a  portion  of  white  fibrous  tissue  (e.g.,  a  small 
piece  of  tendon)  for  a  short  time  in  lime,  or  baryta-water,  or  in  a  solution 
of  common  salt,  or  potassium  permanganate:  those  roagonts  possessing 
the  power  of  dissolving  tlie  cementing  interfibrillar  substance  (whicli  is 
nearly  allied  to  syntonin),  and  thus  separating  the  fibres  from  each  other. 

(/;.)  Yellow  Elastic  Fibres  (Fig.  2S)  arc  of  all  sizes,  from  excossivoly 
fine  (i])i-ils  \\\)  to  fibres  of  considerable  tliickness:  tliey  are  distinguished 


STRUCTURE  OF  THE  ELEMENTARY  TISSUES. 


31 


from  white  fibres  by  the  following  characters: — (1.)  Their  great  power  of 
resistance  even  to  the  prolonged  action  of  chemical  reagents,  e.g.,  Caustic 
Soda,  Acetic  Acid,  etc.  (2.)  Their  well-de- 
fined outlines.  (3.)  Their  great  tendency  to 
branch  and  form  networks  by  anastomosis.  (4. ) 
They  very  often  have  a  twisted  corkscrew- 
like appearance,  and  their  free  ends  usually 
curl  up.  (5.)  They  are  of  a  yellowish  tint 
and  very  elastic. 

VARIETIES  OF  CONNECTIVE  TISSUE. 
I.  FiBEOus  Connective  Tissues. 

A. — Chief  Forms. — {a.)  Areolar  Tissue. 

Distribution. — This  variety  has  a  very  wide 
distribution,  and  constitutes  the  subcutaneous, 
subserous  and  submucous  tissue.    It  is  found  ugame^ta7^bflivI^So!^^(?^^^ 
in  the  mucous  membranes,  in  the  true  skin,  in  ^^^'^ 
the  outer  sheaths  of  the  blood-vessels.    It  forms  sheaths  for  muscles, 
nerves,  glands,  and  the  internal  organs,  and,  penetrating  into  their  in- 
terior, supports  and  connects  the  finest  parts. 

Structure. — To  the  naked  eye  it  appears,  when  stretched  out,  as  a 
fleecy,  white,  and  soft  mesh  work  of  fine  fibrils,  with  here  and  there  wider 
films  joining  in  it,  the  whole  tissue  being  evidently  elastic.  The  open- 
ness of  the  meshwork  varies  with  the  locality  from  which  the  specimen  is 
taken.  On  the  addition  of  acetic  acid  the  tissue  swells  up,  and  becomes 
gelatinous  in  appearance.  Under  the  microscope  it  is  found  to  be  made 
up  of  fine  white  fibres,  which  interlace  in  a  most  irregular  manner,  to- 
gether with  a  variable  number  of  elastic  fibres.  These  latter  resist  the 
action  of  acetic  acid  as  above  mentioned,  so  that  when  this  reagent  is 
added  to  a  specimen  of  areolar  tissue,  although  the  white  fibres  swell  up 
and  become  homogeneous,  certain  elastic  fibres  may  still  be  seen  arranged 
in  various  directions,  sometimes  even  appearing  to  pass  in  a  more  or  less 
circular  or  in  a  spiral  manner  round  a  small  mass  of  the  gelatinous  mass 
of  changed  white  fibres.  The  cells  of  the  tissue  are  arranged  in  no  very 
regular  manner,  being  contained  in  the  spaces  (areolse)  between  the  fibres. 
They  communicate,  however,  with  one  another  by  their  branched  pro- 
cesses, and  also  apparently  with  the  cells  forming  the  walls  of  the  capil- 
lary blood-vessels  in  their  neighborhood,  connecting  together  the  fibrils 
in  a  certain  amount  of  albuminous  cemeiit  substance. 

{h.)  White  Fibrous  Tissue. 

Distribution. — Typically  in  tendon;  in  ligaments,  in  the  periosteum 
and  perichondrium,  the  dura  mater,  the  pericardium,  the  sclerotic  coat 


32 


HAOT)-BOOK  OF  PHYSIOLOGY 


of  the  eye,  the  fibrous  sheath  of  the  testicle;  in  the  fasciae  and  aponeurosis 
of  muscles,  and  in  the  sheaths  of  lymphatic  glands. 

Structure. — To  the  naked  eye,  tendons  and  many  of  the  fibrous  mem- 
branes, when  in  a  fresh  state,  present  an  appearance  as  of  watered  silk. 
This  is  due  to  the  arrangement  of  the  fibres  in  wavy  parallel  bundles. 
Under  the  microscope,  the  tissue  appears  to  consist  of  long,  often  parallel, 
wavy  bundles  of  fibres  of  different  sizes.  Sometimes  the  fibres  intersect 
each  other.  The  cells  in  tendons  are  arranged  in  long  chains  in  the 
ground  substance  separating  the  bundles  of  fibres,  and  are  more  or  less 
regularly  quadrilateral  with  large  round  nuclei  containing  nucleoli,  which 
are  generally  placed  so  as  to  be  contiguous  in  two  cells.  Tlie  cells  consist 
of  a  body,  which  is  thick,  from  which  processes  pass  in  various  directions 
into,  and  partially  filling  up  the  spaces  between  the  bundles  of  fibres. 


Fig.  29.  Fig.  30. 

Fig.  29.— Caudal  tendon  of  young  rat,  showing  the  arrangement,  form,  and  structure  of  the  ten- 
don eeUs.    X  3W.  (Klein.) 

Fig.  30.— Transverse  section  of  tendon  from  a  cross-section  of  the  tail  of  a  rabbit,  showing  sheath, 
fibrous  septa,  and  branched  comiective-tissue  corpuscles.  The  spaces  left  white  in  the  dra^\'ing  rep- 
resent the  tendinous  fibres  in  transverse  section.    X  250.  (Klein.) 

The  rows  of  cells  are  separated  from  one  another  by  lines  of  cement  sub- 
stance. The  cell  spaces  can  be  brought  into  view  by  silver  nitrate.  The 
cells  are  generally  marked  by  one  or  more  lines  or  stripes  when  viewed 
longitudinally.  This  appearance  is  really  produced  by  the  laminar  ex- 
tension either  projecting  upward  or  downward, 
(c.)  Yellow  Elastic  Tissue. 

Distrihution. — In  the  ligamentum  nuchje  of  the  ox,  horse,  and  many 
other  animals;  in  the  ligamenta  subflava  of  man;  in  the  arteries,  consti- 
tuting the  fenestrated  coat  of  Ilenle;  in  veins;  in  the  lungs  and  tracliea: 
in  tlie  stylo-hyoid,  thyro-hyoid,  and  crico-thyroid  ligaments;  in  the  true 
vocal  cords. 

Structure. — Elastic  tissue  occurs  in  various  forms,  from  a  structure- 
less, elastic  membrane  to  a  tissue  whoso  cliicf  constituents  are  bundles  of 


STRUCTURE  OF  THE  ELEMENTARY  TISSUES. 


33 


elastic  fibres  crossing  each  other  at  different  angles:  these  varieties  may 
be  classified  as  follows: — 

(a.)  Fine  elastic  fibrils,  which  branch  and  anastomose  to  form  a  net- 
work: this  variety  of  elastic  tissue  occurs  chiefly  in  the  skin  and  mucous 
membranes,  in  subcutaneous  and  submucous  tissue,  in  the  lungs  and  true 
vocal  cords. 

(b.)  Thick  fibres,  sometimes  cylindrical,  sometimes  flattened  like  tape, 
which  branch  and  form  a  network:  these  are  seen  most  typically  in  the 
ligamenta  subflava  and  also  in  the  ligamentum  nuchse  of  such  animals  as 
the  ox  and  horse,  in  which  it  is  largely  developed. 

(c.)  Elastic  membranes  with  perforations,  e.g.,  Henle^s  fenestrated 
membrane:  this  variety  is  found  chiefly  in  the  arteries  and  veins. 

(d.)  Continuous,  homogeneous  elastic  membranes,  e.g.,  Bowman^s 


Fig.  31.  Fig.  32. 

Fig.  31.— Tissue  of  the  jelly  of  Wharton  from  tunbilical  cord.  a.  connective-tissue  corpuscles; 
6.  fasciculi  of  connective  tissue;  c.  spherical  formative  cells.  (Frey.) 

Fig.  32.— Part  of  a  section  of  a  lymphatic  gland,  from  which  the  corpuscles  have  been  for  the 
most  part  removed,  showing  the  adenoid  recticulum.  (Klein  and  Noble  Smith.) 


anterior  elastic  lamina,  and  Descemefs  posterior  elastic  lamina,  both  in 
the  cornea. 

A  certain  number  of  flat  connective  tissue  cells  are  found  in  the 
ground  substance  between  the  elastic  fibres  constituting  this  variety  of 
connective  tissue. 

B. — Special  Forms. — (a.)  Gelatinous  Tissue. 

Distribution. — Gelatinous  connective  tissue  forms  the  chief  part  of 
the  bodies  of  jelly  fish;  it  is  found  in  many  parts  of  the  human  embryo, 
but  remains  in  the  adult  only  in  the  vitreous  humor  of  the  eye.  It  may 
be  best  seen  in  the  last-named  situation,  in  the  "Whartonian  Jelly*'  of  the 
umbilical  cord,  and  in  the  enamel  organ  of  developing  teeth. 
Vol.  I.— 3. 


34 


HAND-BOOK  OF  PHYSIOLOGY. 


Structure. — It  consists  of  cells,  which  in  the  vitreous  humor  are 
rounded,  and  in  the  jelly  of  the  enamel  organ  are  stellate,  imbedded  in  a 
soft  jelly-like  intercellular  substance  which  forms  the  bulk  of  "the  tissue, 
and  which  contains  a  considerable  quantity  of  mucin.  In  the  umbilical 
cord,  that  part  of  the  jelly  immediately  surrounding  the  stellate  cells 
shows  marks  of  obscure  fibrillation. 

(h.)  Adenoid  or  Retiform. 

Distribution. — It  composes  the  stroma  of  the  spleen  and  lymphatic 
glands,  and  is  found  also  in  the  thymus,  in  the  tonsils,  in  the  follicular 
glands  of  the  tongue,  in  Peyer^s  patches  and  in  the  solitary  glands  of  the 
intestines,  and  in  the  mucous  membranes  generally. 

Structure. — Adenoid  or  retiform  tissue  consists  of  a  very  delicate  net- 
work of  minute  fibrils,  formed  originally  by  the  union  of  processes  of 
branched  connective-tissue  corpuscles  the  nuclei  of  which,  however,  are 
visible  only  during  the  early  periods  of  development  of  the  tissue 
(Eig.  32). 

The  nuclei  found  on  the  fibrillar  meshwork  do  not  form  an  essential 
part  of  it.  The  fibrils  are  neither  white  fibrous  nor  elastic  tissue,  as  they 
are  insoluble  in  boiling  water,  although  readily  soluble  in  hot  alkaline 
solutions. 

{c.)  Neuroglia. — This  tissue  forms  the  support  of  the  Kervous  ele- 
ments in  the  Brain  and  Spinal  cord.  It  consists  of  a  very  fine  meshwork 
of  fibrils,  said  to  be  elastic,  and  with  nucleated  plates  which  constitute 
the  connective-tissue  corpuscles  imbedded  in  it. 


Fig.  33.— Portion  of  the  submucous  tissue  of  prra^id  uterus  of  sow.   a,  branched  cells,  more  or  less 
spindle-shaped;  6.  bundles  of  connective  tissue.  (Klein.) 

Development  of  Fibrous  Tissues. — In  the  embryo  the  place  of 
the  fil)rous  tissues  is  at  first  occupied  by  a  mass  of  roundish  cells,  derived 
from  the  "inesobhist." 

These  develop  either  ipto  a  network  of  branched  cells,  or  into  groups 
of  fusiform  cells  (Fig.  33). 

The  cells  are  imbedded  in  a  semi-fluid  albuminous  substance  derived 
either  from  the  cells  themselves  or  from  the  neighboring  blood-vessels; 
this  afterward  forms  the  cement  substance.    In  it  fibres  arc  developed, 


STRUCTURE  OF  THE  ELEMENTARY  TISSUES.  35 

either  by  part  of  the  cells  becoming  fibrils,  the  others  remaining  as  con- 
nective-tissue corpuscles,  or  by  the  fibrils  being  developed  from  the  out- 
side layers  of  the  protoplasm  of  the  cells,  which  grow  up  again  to  their 
original  size  and  remain  imbedded  among  the  fibres.  This  process  gives 
rise  to  fibres  arranged  in  the  one  case  in  interlacing  networks  (areolar 
tissue),  in  the  other  in  parallel  bundles  (white  fibrous  tissue).  In  the 
mature  forms  of  purely  fibrous  tissue  not  only  the  remnants  of  the  cell- 
substance,  but  even  the  nuclei  may  disappear.  The  embryonic  tissue, 
from  which  elastic  &0Yes  are  developed,  is  composed  of  fusiform  cells,  and 
a  structureless  intercellular  substance  by  the  gradual  fibrillation  of  which 
elastic  fibres  are  formed.  The  fusiform  cells  dwindle  in  size  and  event- 
ually disappear  so  completely  that  in  mature  elastic  tissue  hardly  a  trace 
of  them  is  to  be  found:  meanwhile  the  elastic  fibres  steadily  increase  in 
size. 

Another  theory  of  the  development  of  the  connective-tissue  fibrils 
•supposes  that  they  arise  from  deposits  in  the  intercellular  substance  and 
not  from  the  cells  themselves;  these  deposits,  in  the  case  of  elastic  fibres, 
appearing  first  of  all  in  the  form  of  rows  of  granules,  which,  joining 
together,  form  long  fibrils.  It  seems  probable  that  even  if  this  view  be 
correct,  the  cells  themselves  have  a  considerable  influence  in  the  produc- 
tion of  the  deposits  outside  them. 

Functions  of  Areolar  and  Fibrous  Tissue. — The  main  function 
of  connective  tissue  is  mechanical  rather  than  vital:  it  fulfils  the  subsidi- 
ary but  important  use  of  supporting  and  connecting  the  various  tissues 
and  organs  of  the  body. 

In  glands  the  trabeculse  of  connective  tissue  form  an  interstitial  frame- 
work in  which  the  parenchyma  or  secreting  gland-tissue  is  lodged:  in 
muscles  and  nerves  the  septa  of  connective  tissue  support  the  bundles  of 
fibres,  which  form  the  essential  part  of  the  structure. 

Elastic  tissue,  by  virtue  of  its  elasticity,  has  other  important  uses: 
these,  again,  are  mechanical  rather  than  vital.  Thus  the  ligamentum 
nuchae  of  the  horse  or  ox  acts  very  much  as  an  India-rubber  band  in  the 
same  position  would.  It  maintains  the  head  in  a  proper  position  without 
any  muscular  exertion;  and  when  the  head  has  been  lowered  by  the  action 
of  the  flexor  muscles  of  the  neck,  and  the  ligamentum  nuchge  thus 
stretched,  the  head  is  brought  up  again  to  its  normal  position  by  the 
relaxation  of  the  flexor  muscles  which  allows  the  elasticity  of  the  liga- 
mentum nuchse  to  come  again  into  play. 

(a.)  Adipose  Tissue. 

Distrihiifion. — In  almost  all  regions  of  the  human  body  a  larger  or 
smaller  quantity  of  adipose  or  fatty  tissue  is  present;  the  chief  exceptions 
being  the  subcutaneous  tissue  of  the  eyelids,  penis,  and  scrotum,  the 
nymphae,  and  the  cavity  of  the  cranium.  Adipose  tissue  is  also  absent 
from  the  substance  of  many  organs,  as  the  lungs,  liver,  and  others. 


36 


HAI^D-BOOK  OF  PHYSIOLOGY. 


Fatty  matter,  not  in  the  form  of  a  distinct  tissue,  is  also  widely  pres- 
ent in  the  body,  e.g.,  in  the  liver  and  brain,  and  in  the  blood  and  chyle. 

Adipose  tissue  is  almost  always  found  seated  in  areolar  tissue,  and  forms 
in  its  meshes  little  masses  of  unequal  size  and  irregular  shape,  to  which 
the  term  lohules  is  commonly  applied. 

Structure. — Under  the  microscope  adipose  tissue  is  found  to  consist 
essentially  of  little  vesicles  or  cells  which  present  dark,  sharply-defined 
edges  when  viewed  with  transmitted  light:  they  are  about  ^^-^^  or  of 
an  inch  in  diameter,  each  composed  of  a  structureless  and  colorless  mem- 
brane or  bag,  filled  with  fatty  matter,  which  is  liquid  during  life,  but  in 
part  solidified  after  death  (Fig.  34).  A  nucleus  is  always  present  in  some 
part  or  other  of  the  cell- wall,  but  in  the  ordinary  condition  of  the  cell  it 
is  not  easily  or  always  visible. 


Fig.  34.  Fig.  35. 

Fig.  34.— Ordinary  fat-cells  of  a  fat  tract  in  the  omentum  of  a  rat.  (Kiein.) 
Fig.  35.— Group  of  fat-ceUs  (fc)  with  capiUary  vessels  (c).   (Noble  Smith.) 


This  membrane  and  the  nucleus  can  generally  be  brought  into  view  by 
staining  the  tissue:  it  can  be  still  more  satisfactorily  demonstrated  by  ex- 
tracting the  contents  of  the  fat-cells  with  ether,  when  the  shrunken, 
shriveled  membranes  remain  behind.  By  mutual  pressure,  fat-cells  come 
to  assume  a  polyhedral  figure  (Fig.  35). 

The  ultimate  cells  are  held -together  by  capillary  blood-vessels  (Fig. 
35);  while  the  little  clusters  thus  formed  are  grouped  into  small  masses, 
and  lield  so,  in  most  cases,  by  areolar  tissue. 

Tlie  oily  matter  contained  in  the  cells  is  composed  chiefly  of  the  com- 
pounds of  fatty  acids  with  glycerin,  which  are  named  olein,  stearin,  and 
])(dnii,tin. 

Development  of  Adipose  Tissue. — Fat-cells  arc  developed  from 
coimoctivo-tissue  corpuscles:  in  the  infra-orbital  connective-tissue  cells 
may  be  found  ex]iil)iting  every  intermediate  gradation  between  an  ordi- 
nary ])ranchc(l  connective-tissue  corpuscle  and  a  mature  fat-cell.  The 
process  of  development  is  as  follows:  a  few  small  drops  of  oil  make  their 


STRUCTURE  OF  THE  ELEIMENTARY  TISSUES. 


37 


appearance  in  the  protoplasm:  by  their  confluence  a  larger  drop  is  pro- 
duced (Fig.  37):  this  gradually  increases  in  size  at  the  expense  of  the  orig- 
inal protoplasm  of  the  cell,  which  becomes  correspondingly  diminished 
in  quantity  till  in  the  mature  cell  it  only  forms  a  thin  crescentic  film, 
closely  pressed  against  the  cell-wall,  and  with  a  nucleus  imbedded  in  its 
substance  (Figs.  34  and  37). 

■  Under  certain  circumstances  this  process  may  be  reversed  and  fat-cells 
may  be  changed  back  into  connective-tissue  corpuscles.  (Kolliker,  Vir- 
chow. ) 


Fig.  36.  Fig.  37. 

Fig.  36.— Blood-vessels  of  adipose  tissue,  a.  Minute  flattened  fat-lobule,  in  which  the  vessels  only 
are  represented,  a,  the  terminal  artery;  v,  the  primitive  vein;  6,  the  fat  vesicles  of  one  border  of 
the  lobule  separately  represented.  X  100.  b.  Plan  of  the  arrangement  of  the  capillaries  (c)  on  the 
exterior  of  the  vesicles:  more  highly  magnified.    (Todd  and  Bowman.) 

Fig.  37.— a  lobule  of  developing  adipose  tissue  from  an  eight  months'  foetus,  a.  Spherical,  or, 
from  pressure,  polyhedral  cells  with  large  central  nucleus,  surrounded  by  a  finely  reticulated  sub- 
stance staining  uniformly  with  hsematoxylin.  b.  Similar  cells  with  spaces  from  which  the  fat  has 
been  removed  by  oil  of  cloves,  c.  Similar  cells  showing  how  the  nucleus  with  enclosing  protoplasm 
is  being  pressed  towards  periphery,  d.  Nucleus  of  endothehimi  of  investing  capillaries.  (McCarthy.) 
Drawn  by  Treves. 

Vessels  and  Nerves. — A  large  number  of  blood-vessels  are  found  in 
adipose  tissue,  which  subdivide  until  each  lobule  of  fat  contains  a  fine 
meshwork  of  capillaries  ensheathing  each  individual  fat-globule.  Al- 
though nerve  fibres  pass  through  the  tissue,  no  nerves  have  been  demon- 
strated to  terminate  in  it. 

The  Uses  of  Adipose  Tissue. — Among  the  uses  of  adipose  tissue, 
these  are  the  chief: — 

a.  It  serves  as  a  store  of  combustible  matter  which  may  be  re-ab- 
sorbed into  the  blood  when  occasion  requires,  and,  being  burnt,  may 
help  to  preserve  the  heat  of  the  body. 

1).  That  part  of  the  fat  which  is  situate  beneath  the  skin  must,  by  its 
want  of  conducting  power,  assist  in  preventing  undue  waste  of  the  heat 
of  the  body  by  escape  from  the  surface. 


38 


HAND-BOOK  OF  PHYSIOLOGY. 


c.  As  a  packing  material,  fat  serves  very  admirably  to  fill  up  spaces, 
to  form  a  soft  and  yielding  yet  elastic  material  wherewith  to  wrap  tender 
and  delicate  structures,  or  form  a  bed  with  like  qualities  on  which  such 
structures  may  lie,  not  endangered  by  pressure. 

As  good  examples  of  situations  in  which  fat  serves  such  purposes  may 
be  mentioned  the  palms  of  the  hands  and  soles  of  the  feet,  and  the  orbits. 


Fig.  38. — Branched  connective-tissue  corpuscles,  developing  into  fat-cells.   (Klein.  ) 

d.  In  the  long  bones,  fatty  tissue,  in  the  form  known  as  yellow  mar- 
row, fills  the  medullary  canal,  and  supports  the  small  blood-vessels  which 
are  distributed  from  it  to  the  inner  part  of  the  substance  of  the  bone. 

II.  Caetilage. 

Cartilage  or  gristle  exists  in  three  different  forms  in  the  human  body, 
viz.,  1,  Hyaline  cartilage,  2,  Yelloiu  elastic  cartilage,  and  3,  White  fibro- 
cartilage. 

Structure  of  Cartilage. — All  kinds  of  cartilage  are  composed  of 
cells  imbedded  in  a  substance  called  the  matrix :  and  the  apparent  differ- 
ences of  structure  met  with  in  the  various  kinds  of  cartilage  are  more  due 
to  differences  in  the  character  of  the  matrix  than  of  the  cells.  Among 
the  latter,  however,  there  is  also  considerable  diversity  of  form  and  size. 

With  the  exception  of  the  articular  variety,  cartilage  is  invested  by  a 
thin  but  tough  firm  fibrous  membrane  called  the  pericliojidrinm.  On  the 
surface  of  the  articular  cartilage  of  the  fa3tus,  the  perichondrium  is  rep- 
resented by  a  film  of  epithelium;  but  this  is  gradually  worn  away  up  to 
the  margin  of  the  articular  surfaces,  when  by  use  the  parts  begin  to  suffer 
friction. 

Nerves  are  probably  not  supplied  to  any  variety  of  cartilage. 
1.  Hyaline  Cartilage. 

I)istril)nlu))i,. — This  variety  of  cartilage  is  met  with  largely  in  the 
human  body — investing  the  articular  ends  of  bones,  and  forming  the 
costal  cartilages,  the  nasal  carl  iliiges,  and  those  of  tlio  larynx  with  the  ox- 


STKUCTUKE  OF  TUB  ELEMENTARY  TISSUES. 


39 


ception  of  the  epiglottis  and  cornicula  laryngis.  The  cartilages  of  the 
trachea  and  bronchi  are  also  hyaline. 

Structure. — Like  other  cartilages  it  is  composed  of  cells  imbedded  in 
a  matrix.    The  cells,  which  contain  a  nucleus  with  nucleoli,  are  irregular 
in  shape,  and  generally  grouped  together 
in  patches  (Fig.  39).    The  patches  are  ' 
of  various  shapes  and  sizes,  and  placed 
at  unequal  distances  apart.    They  gen- 
erally appear  flattened  near  the  free  sur- 
face of  the  mass  of  cartilage  in  which 
they  are  placed,  and  more  or  less  per- 
pendicular to  the  surface  in  the  more- 
deeply  seated  portions. 

The  matrix  of  hyaline  cartilage  has 
a  dimly  granular  appearance  like  that  of 
ground  glass,  and  in  man  and  the  higher 
animals  has  no  apparent  structure.  In 
some  cartilages  of  the  frog,  however, 
even  when  examined  in  the  fresh  state, 
it  is  seen  to  be  mapped  out  into  polygo- 
nal blocks  or  cell-territories,  each  con- 
taining m  cell  in  the  centre,  and  representing  what  is  generally  called 
the  capsule  of  the  cartilage  cells  (Fig.  40).  Hyaline  cartilage  in  man 
has  really  the  same  structure,  which  can  be  demonstrated  by  the  use  of 
certain  reagents.    If  a  piece  of  human  hyaline  cartilage  be  macerated 


Fig.  39.— Ordinary  hyaline  cartilage  from 
trachea  of  a  child.  The  cartilage  cells  are 
enclosed  singly  or  in  pairs  in  a  capsule  of 
hyaUne  substance.  X  150  diams.  (Klein 
and  Noble  •Smith.) 


Fig.  40.— Fresh  cartilage  from  the  Triton.   (A.  RoUett.) 


for  a  long  time  in  dilute  acid  or  in  hot  water  95"— 113°  F.  (35°  to 
45°  C),  the  matrix,  which  previously  appeared  quite  homogeneous,  is 
found  to  be  resolved  into  a  number  of  concentric  lamellae,  like  the  coats 


40 


HAND-BOOK  OF  PHYSIOLOGY. 


of  an  onion,  arranged  round  each  cell  or  group  of  cells.  It  is  thus 
shown  to  consist  of  nothing  but  a  number  of  large  systems  of  capsules 
which  have  become,  fused  with  one  another 

The  cavities  in  the  matrix  in  which  the  cells  lie  are  connected  to- 
gether by  a  series  of  branching  canals,  very  much  resembling  those  in  the 
cornea:  through  these  canals  fluids  may  make  their  way  into  the  depths 
of  the  tissue. 

In  the  hyaline  cartilage  of  the  ribs,  the  cells  are  mostly  larger  than  in 
the  articular  variety,  and  there  is  a  tendency  to  the  development  of  fibres 
in  the  matrix.  The  costal  cartilages  also  frequently  become  calcified  in 
old  age,  as  also  do  some  of  those  of  the  larynx.  Fat-globules  may  also  be 
seen  in  many  cartilages. 

In  articular  cartilage  the  cells  are  smaller,  and  arranged  vertically  in 
narrow  lines  like  strings  of  beads. 

Temporary  Cartilage. — In  the  foetus,  cartilage  is  the  material  of 
which  the  bones  are  first  constructed;  the  ^ 'model"  of  each  bone  being 
laid  down,  so  to  speak,  in  this  substance.  In  such  cases  the  cartilage  is 
termed  temporary.  It  closely  resembles  the  ordinary  hyaline  kind;  the 
cells,  however,  are  not  grouped  together  after  the  fashion  just  described, 
but  are  more  uniformly  distributed  throughout  the  matrix. 

A  variety  of  temporary  hyaline  cartilage  which  has  scarcely  any  matrix 
is  found  in  the  human  subject  only  in  early  foetal  life,  when  it  constitutes 
the  chorda  dorsalis. 

Nutrition  of  Cartilage. — Hyaline  cartilage  is  reckoned  among  trhcj 
so-called  non-vascular  structures,  no  blood-vessels  being  supplied  directly 
to  its  own  substance;  it  is  nourished  by  those  of  the  bone  beneath. 
When  hyaline  cartilage  is  in  thicker  masses,  as  in  the  case  of  the  cartila,aes 
of  the  ribs,  a  few  blood-vessels  traverse  its  substanc^,.  The  distinction, 
however,  between  all  so-called  vascular  and  non-vascvlar  parts,  is  at  the 
best  a  very  artificial  one. 

2.  Yellow  Elastic  Cartilage. 

Distrihiition. — In  the  external  ear,  in  the  epiglottis  and  cornicula 
laryngis,  and  in  the  Eustachian  tube. 

Structure. — The  cells  are  rounded  or  oval,  with  well-marked  nuclei 
and  nucleoli  (Fig.  41).  The  matrix  in  which  they  are  seated  is  composed 
almost  entirely  of  fine  elastic  fibres,  which  form  an  intricate  interlace- 
ment about  the  cells,  and  in  their  general  characters  arc  allied  to  the  yel- 
low variety  of  fibrous  tissue:  a  small  and  variable  quantity  of  hyaline  in- 
tercellular substance  is  also  usually  present. 

A  variety  of  elastic  cartilage,  sometimes  called  cellular,  may  be  obtained 
from  the  external  ear  of  rats,  mice,  or  other  small  mammals.  It  is  com- 
])()S(m1  almost  entirely  of  cells  (hence  the  name),  which  are  packed  very 
closely,  with  little  or  no  matrix.    When  present  the  matrix  consists  of 


STRUCTURAL   BASIS  OF  THE  HUMAN  BODY. 


41 


very  fine  fibres,  which  twine  about  the  cells  in  various  directions  and 
enclose  them  in  a  kind  of  network. 

3.  White  Fibro-Cartilage. 

Distribtttion. — The  different  situations  in  which  white  fibro-cartilage 
is  found  have  given  rise  to  the  following  classification: — 

1.  Inter-articular  fibro-cartilage,  e.g.,  the  semilunar  cartilages  of 
the  knee-joint. 


Fig.  41. 


Fig.  42. 


Fig.  41. — Section  of  the  epiglottis.  (Baly.) 

Fig.  42.— Tranverse  section  through  the  intervertebral  cartilage  of  the  tail  of  mouse,  showing 
lameUse  of  fibrous  tissue  with  cartilage  ceUs  arranged  in  rows  between  them.  The  ceUs  are  seen  in 
profile,  and  being  flattened,  appear  staflE-shaped.  Each  cell  lies  in  a  capsule.  X  350.  (Klein  and 
Noble  Smith.) 

2.  Circumferential  or  marginal,  as  on  the  edges  of  the  acetabulum 
and  glenoid  cavity. 

3.  Connecting ,  e.g.,  the  inter-vertebral  fibro-cartilages. 

4.  In  the  sheatlis  of  tendons,  and  sometimes  in  their  substance.  In 
the  latter  situation,  the  nodule  of  fibro-cartilage  is  called  a  sesamoid  fibro- 
cartilage,  of  which  a  specimen  may  be 
found  in  the  tendon  of  the  tibialis  posti- 
cus, in  the  sole  of  the  foot,  and  usually 
in  the  neighboring  tendon  of  the  peroneus 
longus. 

Structure. — White  fibro-cartilage  (Fig. 
43),  which  is  much  more  widely  distribu- 
ted throughout  the  body  than  the  forego- 
ing kind,  is  composed,  like  it,  of  cells  and 
a  matrix;  the  latter,  however,  being  made 
up  almost  entirely  of  fibres  closely  resem- 
bling those  of  white  fibrous  tissue. 

In  this  kind  of  fibro-cartilage  it  is  not 
unusual  to  find  a  great  part  of  its  mass 
composed  almost  exclusively  of  fibres,  and  deriving  the  name  of  cartilage 
only  from  the  fact  that  in  another  portion,  continuous  with  it,  cartilage 
cells  may  be  pretty  freely  distributed. 


Fig.  43.— White  fibro-cartilage  from 
an  intervertebral  ligament.  (Klein  and 
Noble  Smith.) 


42 


iia:sd-book  of  physiology 


Functions  of  Cartilage. — Cartilage  not  only  represents  in  tlie  foetus 
the  bones  which  are  to  be  formed  (temporary  cartilage),  but  also  offers  a 
firm,  but  more  or  less  yielding,  framework  for  certain  j^arts  in  the  de- 
yeloped  body,  possessing  at  the  same  time  strength  and  elasticity.  It 
maintains  the  shape  of  tubes  as  in  the  larynx  and  trachea.  It  affords 
attachment  to  muscles  and  ligaments;  it  binds  bones  together,  yet  allows 
a  certain  degree  of  movement,  as  between  the  Yertebrte;  it  forms  a  firm 
framework  and  protection,  yet  without  undue  stiffness  or  weight,  as  in 
the  pinna,  larynx,  and  chest  walls;  it  deepens  joint  cavities,  as  in  the 
acetabulum,  without  unduly  restricting  the  movements  of  the  bones. 

Development  of  Cartilage. — Cartilage  is  developed  out  of  an  em- 
bryonal tissue,  consisting  of  cells  with  a  very  small  quantity  of  intercel- 
lular substance:  the  cells  multiply  by  fission  within  the  cell-capsules  (Fig. 
6);  while  the  capsule  of  the  parent  cell  becomes  gradually  fused  with  the 
surrounding  intercellular  substance.  A  repetition  of  this  process  in  the 
young  cells  causes  a  rapid  growth  of  the  cartilage  by  the  multiplication 
of  its  cellular  elements  and  corresponding  increase  in  its  matrix. 

III.  BOXE. 

Chemical  Composition. — Bone  is  composed  of  eartliy  and  animal 
matter  in  the  proportion  of  about  67  per  cent,  of  the  former  to  33  per 
cent,  of  the  latter.  The  earthy  matter  is  composed  chiefly  of  calcium 
phosphate,  but  besides  there  is  a  small  quantity  (about  11  of  the  67  per 
cent.)  of  calcium  carbonate  and  fluoride,  and  magnesium  ^^hosphate. 

The  animal  matter  is  resolved  into  gelatin  by  boiling. 

The  earthy  and  animal  constituents  of  bone  are  so  intimately  blended 
and  incorj^orated  the  one  with  the  other,  that  it  is  only  by  chemical 
action,  as,  for  instance,  by  heat  in  one  case  and  by  the  action  of  acids 
in  another,  that  they  can  be  separated.  Their  close  union,  too,  is  further 
shown  b}"  the  fact  that  when  by  acids  the  earthy  matter  is  dissolved  out, 
or,  on  the  other  hand,  when  the  animal  part  is  burnt  out,  tlie  shape  of 
the  bone  is  alike  preserved. 

The  proportion  between  these  two  constituents  of  bone  varies  in  dif- 
ferent bones  in  the  same  individual,  and  in  the  same  bone  at  different 
ages. 

Structure. — To  the  naked  eye  there  appear  two  kinds  of  structure  in 
different  bones,  and  in  different  parts  of  tlio  same  bone,  namely,  the  denfte 
or  compact,  and  the  spongy  or  cancellous  tissue. 

Tlius,  in  making  a  longitudinal  section  of  a  long  bone,  as  the  humerus 
or  femur,  tlie  articular  extremities  are  found  capi)ed  on  their  surface  by 
a  thin  shell  of  compact  bone,  wliile  their  interior  is  made  up  of  tlie 
spongy  or  cancellous  tissue.  The  shaft,  on  the  other  hand,  is  formed 
almost  entirely  of  a  thick  layer  of  the  compact  bone,  and  this  surrounds 


STRUCTURE  OF  THE  ELEMENTARY  TISSUES. 


43 


a  central  canal,  the  medullary  cavity — so  called  from  its  containing  the 
medulla  or  marrow. 

In  the  flat  bones,  as  the  parietal  bone  or  the  scapula,  one  layer  of  the 
cancellous  structure  lies  between  two  layers  of  the  compact  tissue,  and 
in  the  short  and  irregular  bones,  as  those  of  the  carpus  and  tarsus,  the 
cancellous  tissue  alone  fills  the  interior,  while  a  thin  shell  of  compact 
bone  forms  the  outside. 

Marrow. — There  are  two  distinct  varieties  of  marrow — the  red  and 
yelloiu. 

Red  marrow  is  that  variety  which  occupies  the  spaces  in  the  cancel- 
lous tissue;  it  is  highly  vascular,  and  thus  maintains  the  nutrition  of  the 
spongy  bone,  the  interstices  of  which  it  fills.  It  contains  a  few  fat-cells 
and  a  large  number  of  marrow-cells,  many  of  which  are  undistinguishable 


Fig.  44. — Cells  of  the  red  marrow  of  the  guinea  pig,  highly  magnified,  a,  a  large  cell,  the  nucleus 
of  wliich  appears  to  be  partly  divided  into  three  by  constrictions;  6,  a  cell,  the  nucleus  of  which 
shows  an  appearance  of  being  constricted  into  a  number  of  smaller  nuclei;  c,  a  so-called  giant  cell, 
or  myeloplaxe,with  many  nuclei;  d,  a  smaller  myeloplaxe,  with  three  nuclei;  e — i,  proper  cells  of  the 
marrow.   (E.  A.  Schafer.) 

from  lymphoid  corpuscles,  and  has  for  a  basis  a  small  amount  of  fibrous 
tissue.  Among  the  cells  are  some  nucleated  cells  of  very  much  the  same 
tint  as  colored  blood-corpuscles.  There  are  also  a  few  large  cells  with 
many  nuclei,  termed  "giant-cells^^  (myeloplaxes)  which  are  derived  from 
over- growth  of  the  ordinary  marrow- cells  (Fig.  44). 

Yelloiv  marrow  fills  the  medullary  cavity  of  long  bones,  and  consists 
chiefly  of  fat-cells  with  numerous  blood-vessels;  many  of  its  cells  also  are 
in  every  respect  similar  to  lymphoid  corpuscles. 

From  these  marrow-cells,  especially  those  of  the  red  marrow,  are 
derived,  as  we  shall  presently  show,  large  quantities  of  red  blood-cor- 
puscles. 

Periosteum  and  Nutrient  Blood-vessels. — The  surfaces  of  bones, 
except  the  part  covered  with  articular  cartilage,  are  clothed  by  a  tough, 
fibrous  membrane,  the  periosteum;  and  it  is  from  the  blood-vessels  which 
are  distributed  in  this  membrane,  that  the  bones,  especially  their  more 
compact  tissue,  are  in  great  part  supplied  with  nourishment, — minute 


44 


HAND-BOOK  OF  PHYSIOLOGY. 


branches  from  the  periosteal  vessels  entering  the  little  foramina  on  tlie 
surface  of  the  bone,  and  finding  their  way  to  the  Haversian  canals,  to  be 
immediately  described.  The  long  bones  are  supplied  also  by  a  proper 
nutrient  artery  Avhich,  entering  at  some  part  of  the  shaft  so  as  to  reach 
the  medullary  canal,  breaks  up  into  branches  for  the  supply  of  the  mar- 
row, from  which  again  small  vessels  are  distributed  to  the  interior  of  the 
bone.  Other  small  blood-vessels  pierce  the  articular  extremities  for  the 
supply  of  the  cancellous  tissue. 

Microscopic  Structure  of  Bone. — Notwithstanding  the  differences 
of  arrangement  just  mentioned,  the  structure  of  all  bone  is  found  under 
the  microscope  to  be  essentially  the  same. 


Fig.  45. — Transverse  section  of  compact  bony  tissue  (of  humerus).  Three  of  the  Haversian 
canals  are  seen,  with  their  concentric  rings;  also  the  corpuscles  or  lacunas,  with  the  canaliculi  extend- 
ing from  them  across  the  directi(>n  of  the  lamelljB.  The  Haversian  apertures  had  got  filled 
with  debris  in  grinding  down  tlie  section,  and  therefore  appear  black  in  the  figure,  which  represents 
the  object  as  viewed  with  transmitted  light.  The  Haversian  sj-stems  are  so  closely  packed  in  this 
section,  that  scarcelj-  any  interstitial  lamellae  are  visible,    x  150.  (Sharpe}*.) 

Examined  with  a  rather  high  power  its  substance  is  found  to  contain 
a  multitude  of  little  irregular  spaces,  approximately  fusiform  in  shape, 
called  lacunce,  with  very  minute  canals  or  canaJicnJi,  as  they  are  termed, 
leading  from  them,  and  anastomosing  with  similar  little  jirolongations 
from  other  lacunae  (Fig.  45).  In  very  thin  layers  of  bone,  no  other  canals 
than  these  may  be  visible;  but  on  making  a  transverse  section  of  tlie 
compact  tissue  as  of  a  long  bone,  e.g.,  the  humerus  or  ulna,  the  arrange- 
ment shown  in  Fig.  45  can  be  seen. 

The  bone  seems  mapped  out  into  small  circular  districts,  at  or  about 
the  centre  of  each  of  which  is  a  bole,  and  around  this  an  appearance  as 
of  concentric  layers — the  Jarnnw  and  raiutUculi  following  the  same  con- 
centric phm  of  distribution  around  the  small  hole  in  the  centre,  with 
which,  indeed,  they  communicate. 


STRUCTURE  OF  THE  ELEMENTARY  TISSUES. 


45 


On  making  a  longitudinal  section,  the  central  holes  are  found  to  be 
sipiply  the  cut  extremities  of  small  canals  which  run  lengthwise  through 
the  bone,  anastomosing  with  each  other  by  lateral  branches  (Fig.  46), 
and  are  called  Haversian  canals,  after  the  name  of  the  physician,  Clopton 
Havers,  who  first  accurately  described  them.  The  Haversian  canals,  the 
average  diameter  of  which  is  -^-^  of  an  inch,  contain  blood-vessels,  and 
by  means  of  them  blood  is  conveyed  to  all,  even  the  densest  parts  of  the 
bone;  the  minute  canaliculi  and  lacunae  absorbing  nutrient  matter  from 
the  Haversian  blood-vessels,  and  conveying  it  still  more  intimately  to  the 
very  substance  of  the  bone  which  they  traverse. 

The  blood-vessels  enter  the  Haversian  canals  both  from  without,  by 


Fig.  46.  Fig.  47. 

Fig.  46. — Longitudinal  section  of  human  ulna,  showing  Haversian  canal,  lacunae,  and  canaliculi. 
(RoUett.) 

Fig.  47.— Bone  corpuscles  with  their  processes  as  seen  in  a  thin  section  of  human  bone.  (RoUett.) 


traversing  the  small  holes  which  exist  on  the  surface  of  all  bones  beneath 
the  periosteum,  and  from  within  by  means  of  small  channels  which 
extend  from  the  medullary  cavity,  or  from  the  cancellous  tissue.  The 
arteries  and  veins  usually  occupy  separate  canals,  and  the  veins,  which 
are  the  larger,  often  present,  at  irregular  intervals,  small  pouch-like 
dilatations. 

The  lacuncB  are  occupied  by  branched  cells  (bone-cells,  or  bone-cor- 
puscles) (Fig.  47),  which  very  closely  resemble  the  ordinary  branched 
connective-tissue  corpuscles;  each  of  these  little  masses  of  protoplasm 
ministering  to  the  nutrition  ot  the  bone  immediately  surrounding  it, 
and  one  lacunar  corpuscle  communicating  with  another,  and  with  its  sur- 
rounding district,  and  with  the  blood-vessels  of  the  Haversian  canals,  by 


46 


HAISTD-BOOK  OF  PHYSIOLOaY. 


means  of  the  minute  streams  of  fluid  nutrient  matter  which  occupy  the 
canaliculi. 

It  will  be  seen  from  the  above  description  that  bone  is  essentially  con- 
nective-tissue impregnated  with  lime  salts:  it  bears  a  very  close  resem- 
blance to  what  may  be  termed  typical  connective-tissue  such  as  the 
substance  of  the  cornea.  The  bone-corpuscles  Avith  their  processes,  occu- 
pying the  lacunae  and  canaliculi,  correspond  exactly  to  the  cornea-cor- 
puscles lying  in  branched  spaces;  while  the  finely  fibrillated  structure  of 
the  bone-lamellae,  to  be  presently  described,  resembles  the  fibrillated  sub- 
stance of  the  cornea  in  which  the  branching  spaces  lie. 

Lamellae  of  Compact  Bone. — In  the  shaft  of  a  long  bone  three 
distinct  sets  of  lamellse  can  be  clearly  recognized. 

(1.)  General  or  fundamental  lamella;  which  are  most  easily  traceable 
just  beneath  the  periosteum,  and  around  the  medullary  cavity,  forming 
around  the  latter  a  series  of  concentric  rings.  At  a  little  distance  from 
the  medullary  and  periosteal  surfaces  (in  th§  deeper  portions  of  the  bone) 
they  are  more  or  less  interrupted  by 

(2.)  Sioecial  or  Haversian  lamellae,  which  are  concentrically  arranged 
around  the  Haversian  canals  to  the  number  of  six  to  eighteen  around 
each. 

(3.)  Interstitial  lamellae,  which  connect  the  systems  of  Haversian 
lamellae,  filling  the  spaces  between  them,  and  consequently  attaining 
their  greatest  development  where  the  Haversian 
systems  are  few,  and  vice  versa. 

The  ultimate  structure  of  the  lamellcB  appears 
to  be  reticular.  If  a  thin  film  be  peeled  off  the 
surface  of  a  bone,  from  which  the  earthy  matter  has 
been  removed  by  acid,  and  examined  with  a  high 
power  of  the  microscope,  it  will  be  found  com- 
posed of  a  finely  reticular  structure,  formed  appar- 
ently of  very  slender  fibres  decussating  obliquely, 
but  coalescing  at  the  points  of  intersection,  as  if 
here  the  fibres  were  fused  rather  than  woven 

Fig.  48.— Thin  layer  peeled     ,  -o\       /oi  \ 

off  from  a  softened  bone,   together  (Ing.  48).  (bharpcy.) 

This  fierure,  Avhich  is  intend-  -r  ^  xi  x-iTn 

ed  to  represent  the  reticular  In  mauyplaccs  thcsc  reticular  lamellae  are 

T^^^r-:l^Ti^'£^^  perforated  by  tapering  fibres  {ClavicuU  of  Gagli- 

7^:n^^lt^"^^ly^^^  ardi),  resembling  in  character  the  ordinary  white 

400.  (Sharpey.)  ^^^^  ^j^^g^j^  fibrous  tissuc,  whicli  bolt  the 

neighboring  lamellae  together,  and  may  be  drawn  out  when  tlie  latter  are 
torn  asunder  (Fig.  49).  These  perforating  fibres  originate  from  ingrow- 
ing processes  of  the  periosteum,  and  in  the  adult  still  retain  their  con- 
nection with  it. 

Development  of  Bone. — l^^'rom  tlie  point  of  view  of  tlioir  dovol(^p- 
moiit,  all  b()iH!S  may  be  subdivided  into  two  classes. 


STRUCTUEE  OF  THE  ELEMENTARY  TISSUES. 


47 


(a.)  Those  wliich  iire  ossified  directly  in  7nembrane,  e.g.y  the  bones 
forming  the  vault  of  the  skull,  parietal,  frontal. 

{jb.)  Those  whose  form,  jjrevious  to  ossification,  is  laid  down  in  hyaline 
cartilage,  e.g.,  humerus,  femur. 

The  process  of  development,  pure  and  simple,  may  be  best  studied 
in  bones  which  are  not  preceded  by  cartilage — "membrane-bones"  {e.g., 
parietal);  and  without  a  knowledge  of  this  process  (ossification  in  mem- 
irane),  it  is  impossible  to  understand  the  much  more  complex  series  of 


Fig.  49.— Lamellae  torn  off  from  a  decalcified  human  parietal  bone  at  some  depth  from  the  sur- 
face, a,  a  lamella,  showing  reticular  fibres;  6,  5,  darker  part,  where  several  lameUae  are  superposed; 
c,  perforating  fibres.  Apertures  through  which  perforating  fibres  had  passed,  are  seen  especially  in 
the  lower  part,  a,  a,  of  the  figm-e.   (Allen  Thomson.) 

changes  through  which  such  a  structure  as  the  cartilaginous  femur  of  the 
foetus  passes  in  its  transformation  into  the  body  femur  of  the  adult  (ossi- 
fication in  cartilage). 

Ossification  in  Membrane. — The  membrane  or  periosteum  from 
which  such  a  bone  as  the  parietal  is  developed  consists  of  two  layers — an 
external ^5row5,  and  an  internal  cellular  or  osteogenetic.  • 

The  external  one  consists  of  ordinary  connective-tissue,  being  com- 
posed of  layers  of  fibrous  tissue  with  branched  connective-tissue  corpuscles 
here  and  there  between  the  bundles  of  fibres.  The  internal  layer  consists 
of  a  network  of  fine  fibrils  with  a  large  number  of  nucleated  cells,  some 
of  which  are  oval,  others  drawn  out  into  a  long  branched  process,  and 
others  branched:  it  is  more  richly  supplied  with  capillaries  than  the  outer 
layer.  The  relatively  large  number  of  its  cellular  elements,  their  varia- 
bility in  size  and  shape,  together  with  the  abundance  of  its  blood-vessels, 
clearly  mark  it  out  as  the  portion  of  the  periosteum  which  is  imm-ediately 
concerned  in  the  formation  of  bone. 

In  such  a  bone  as  the  parietal,  the  deposition  of  bony  matter,  which 
is  preceded  by  increased  vascularity,  takes  place  in  radiating  spicul^e. 


48 


HA]S^D-BOOK  OF  PHYSIOLOGY. 


starting  from  a  "centre  of  ossification/^  and  shooting  out  in  all  directions 
toward  the  peripher}-;  while  the  bone  increases  in  thickness  by  the  depo- 
sition of  successive  layers  beneath  the  periosteum.  The  finely  fibrillar 
network  of  the  deeper  or  osteogenetic  layer  of  the  periosteum  becomes 
transformed  into  bone-matrix  (the  minute  structure  of  which  has  been 
already  (p.  46)  described  as  reticular),  and  its  cells  into  bone-corpuscles. 
On  the  young  bone  trabeculge  thus  formed,  fresh  layers  of  cells  (osteo- 
blasts) from  the  osteogenetic  layer  are  developed  side  by  side,  lining  the 
irregular  spaces  like  an  epithelium  (Fig.  50,  h).  Lime-salts  are  deposited 
in  the  circumferential  part  of  each  osteoblast,  and  thus  a  ring  of  osteo- 
blasts gives  rise  to  a  ring  of  bone  with  the  remaining  uncalcified  portions 
of  the  osteoblasts  imbedded  in  it  as  bone-corpuscles  (Fig.  50). 


Fig.  50.— Osteoblasts  from  the  parietal  bone  of  a  human  embryo,  thirteen  weeks  old,  a,  bony- 
septa  with  the  ceUs  of  the  lacunse:  h.  layers  of  osteoblasts;  c,  the  latter  in  transition  vc  bone  cor- 
puscles.  Highly  magnified.  (Gegenbaur.) 

Thus,  the  primitive  spongy  bone  is  formed,  whose  irregular  branch- 
ing spaces  are  occupied  by  processes  from  the  osteogenetic  layer  of  the 
periosteum  with  numerous  blood-vessels  and  osteoblasts.  Portions  of  this 
primitive  spongy  bone  are  re-absorbed;  the  osteoblasts  being  arranged  in 
concentric  successive  layers  and  thus  giving  rise  to  concentric  Haversian 
latfiellae  of  bone,  until  the  irregular  space  in  the  centre  is  reduced  to  a 
well-formed  Haversian  canal,  the  portions  of  the  primitive  spongy  bone 
between  the  Haversian  systems  remaining  as  interstitial  or  ground- 
lamellae  (p.  46).  The  bulk  of  the  primitive  spongy  bone  is  thus  gradu- 
ally converted  into  compact  bonj^-tissue  with  Haversian  canals.  Tliose 
portions  of  the  in-growths  from  the  deeper  layer  of  the  periosteum  which 
are  not  converted  into  bone  remain  in  the  spaces  of  the  cancellous  tissue 
as  the  red  marrow. 

Ossification  in  Cartilage. — Under  this  heading,  taking  the  femur  as 
a  typical  example,  we  may  consider  the  process  by  which  the  solid  carti- 
laginous rod  which  represents  it  in  the  foetus  is  converted  into  tlie  hollow 
cylinder  of  compact  bone  with  expanded  ends  of  cancellous  tissue  which 
forms  the  adult  femur;  bearing  in  mind  the  fact  that  this  fcotal  cartilag- 


STRUCTURE  OF  THE  ELEMENTARY  TISSUES. 


49 


inous  femur  is  many  times  smaller  than  the  medullary  cavity  even  of  the 
shaft  of  the  mature  bone,  and,  therefore,  that  not  a  trace  of  the  original 
cartilage  can  be  present  in  the  femur  of  the  adult.  Its  purpose  is  indeed 
purely  temporary;  and,  after  its  calcification,  it  is  gradually  and  entirely 
re-absorbed  as  will  be  presently  explained. 


Fia.  51.  Fig.  52. 

Fift.  51.— From  a  transverse  section  through  part  of  foetal  jaw  near  the  extreme  periosteum, 
in  the  state  of  spongy  bone,  p,  fibrous  layer  of  periosteum ;  b,  osteogenetic  layer  of  periosteum; 
o,  osteoblasts;  c,  osseous  substance,  containing  many  bone  corpuscles.   X  300.  (Schofield.) 

Fig.  52. — Ossifying  cartilage  showing  loops  of  blood-vessels. 


The  cartilaginous  rod  which  forms  the  fcBtal  femur  is  sheathed  in  a, 
membrane  termed  the  pericliondrium,  which  so  far  resembles  the  perios- 
teum described  above,  that  it  consists  of  two  layers,  in  the  deeper  one  of 
which  spheroidal  cells  predominate  and  blood-vessels  abound,  while  the: 
outer  layer  consists  mainly  of  fusiform  cells  which  are  in  the  mature 
tissue  gradually  transformed  into  fibres.  Thus,  the  differences  between 
Vol.  I.— 4. 


50 


HAND-BOOK  OF  PHYSIOLOGY. 


the  foetal  perichondrium  and  the  periosteum  of  the  adult  are  such  as 
usually  exist  between  the  embryonic  and  mature  forms  of  connective- 
tissue. 

Between  the  hyaline  cartilage  of  which  the  foetal  femur  consists  and 
the  bony  tissue  forming  the  adult  femur,  two  intermediate  stages  exist — 
viz.,  calcified  cartilage,  and  embryonic  spongy  bone.  These  tissues, 
which  successively  occupy  the  place  of  the  foetal  cartilage,  are  in  suc- 
cession entirely  re-absorbed,  and  their  place  taken  by  true  bone. 

The  process  by  which  the  cartilaginous  is  transformed  into  the  bony 


Fig.  53.  Fig.  54. 


Fig.  53.— Longitudinal  section  of  ossifying  cartilage  from  the  humerus  of  a  foetal  sheep.  Calci- 
fied trabeculae  are  seen  extending  between  the  columns  of  cartilage  cells,  c,  cartilage  cells.  X  140. 
(Sharpey.) 

Fig.  .54.— Transverse  section  of  a  portion  of  a  metacarpal  bone  of  a  foetus,  showing— 1.  fibrous 
layer  of  periosteum;  2,  osteogenetic  layer  of  ditto;  3,  periosteal  bone;  4,  cartilage  with  matrix  gradu- 
ally becoming  calcified,  as  at  5,  with  cells  in  primary  areola?;  beyond  5  the  calcified  matrix  is  being 
entirely  replaced  by  spongy  bone.    X  200.   (V,  D.  Harris.) 

femur  may  be  dividea  for  the  sake  of  clearness  into  the  following  six 
stages: 

Stage  I. — Vascularization  of  the  Cartilage. — Processes  from 
the  osteogcnetic  or  cclluhir  layer  of  tlie  pericliondrium  containing  blood- 
vessels grow  into  the  substance  of  the  cartilage  much  as  ivy  insinuates  it- 
self into  the  cracks  and  crcvi(H\s  of  a  wall.  Thus  the  substance  of  the  car- 
tilage, which  previously  contained  no  vessels,  is  traversed  by  a  number  of 


STEUCTUEE  OF  THE  ELEMENTAEY  TISSUES. 


51 


branched  anastomosing  channels  formed  by  the  enlargement  and  coales- 
cence of  the  spaces  in  which  the  cartilage-cells  lie,  and  containing  loops 
of  blood-vessels  (Fig.  52)  and  spheroidal-cells  which  will  become  osteo- 
blasts. 

Stage  2. — Calcification  of  Cartilaginous  Matrix. — Lime-salts 
are  next  deposited  in  the  form  of  fine  granules  in  the  hyaline  matrix  of 
the  cartilage,  which  thus  becomes  gradually  transformed  into  a  number 
of  calcified  trabeculse  (Fig.  54,  forming  alveolar  spaces  {yrimary  areolce) 
containing  cartilage  cells.  By  the  absorption  of  some  of  the  trabeculae 
larger  spaces  arise,  which  contain  cartilage-cells  for  a  very  short  time 
only,  their  places  being  taken  by  the  so-called  osteogenetic  layer  of  the 
perichondrium  (before  referred  to  in  Stage  1)  which  constitutes  the  pri- 
mary marrow.  The  cartilage-cells,  gradually  enlarging,  become  more 
transparent  and  finally  undergo  disintegration. 

Stage  3. — Substitution  of  Embryonic  Spongy  Bone  for  Car- 
tilage.— ^The  cells  of  the  primary  marrow  arrange  themselves  as  a  con- 
tinuous layer  like  epithelium  on  the 
calcified  trabeculae  and  deposit  a  layer 
of  bone,  which  ensheathes  the  calcified 
trabeculae:  these  calcified  trabeculae, 
encased  in  their  sheaths  of  young  bone, 
become  gradually  absorbed,  so  that 
finally  we  have  trabeculae  composed  en- 
tirely of  spongy  bone,  all  trace  of  the 
original  calcified  cartilage  having  dis- 
appeared. It  is  probable  that  the  large 
multinucleated  giant-cells  termed  ' 'os- 
teoclasts" by  KoUiker,  which  are  de- 
rived from  the  osteoblasts  by  the  mul- 
tiplication of  their  nuclei,  are  the 
agents  by  which  the  absorption  of  cal- 
cified cartilage,  and  subsequently  of 
embryonic  spongy  bone,  is  carried  on 
(Fig.  55,  g).  At  any  rate  they  are 
almost  always  found  wherever  absorp- 
tion is  in  progress. 

Stages  2  and  3  are  precisely  similar  to  what  goes  on  in  the  growing 
shaft  of  a  bone  which  is  increasing  in  length  by  the  advance  of  the  pro- 
cess of  ossification  into  the  intermediary  cartilage  between  the  diaphysis 
and  epiphysis.  In  this  case  the  cartilage-cells  become  flattened  and, 
multiplying  by  division,  are  grouped  into  regular  columns  at  right  angles 
to  the  plane  of  calcification,  while  the  process  of  calcification  extends 
into  the  hyaline  matrix  between  them  (Figs.  52  and  53). 

Stage  4.— Substitution  of  Periosteal  Bone  for  the  Primary 


Fig.  55.— a  small  isolated  mass  of  bone  next 
the  periosteum  of  the  lower  jaw  of  human 
foetus,  a,  osteogenetic  layer  of  periosteum. 
G,  multinuclear  giant  cells,  the  one  on  the  left 
acting  here  probably  like  an  osteoclast.  Above 
c,  the  osteoblasts  are  seen  to  become  sur- 
rounded by  an  osseous  matrix.  (Klein  and 
Noble  Smith.) 


52 


HAND-BOOK  OF  PHYSIOLOGY. 


Embryonic  Spongy  Bone. — The  embryonic  spongy  bone,  formed  as 
above  described,  is  simply  a  temporary  tissue  occupying  the  place  of  the 
foetal  rod  of  cartilage,  once  representing  the  femur;  and  the  stages  1,  2, 
and  3  show  the  successive  changes  which  occur  at  the  centime  of  the  shaft. 
Periosteal  bone  is  now  deposited  in  successive  layers  beneath  the  perios- 
teum, i.e.,  at  the  circumference  of  the  shaft,  exactly  as  described  in  the 


Fig.  56.— Transverse  section  tlirough  the  tibia  of  a  foetal  kitten  semi-diagrammatic.  X  60.  P, 
Periostemn.  O,  osteogenetic  layer  of  the  periosteum,  showing  the  ostet>blasts  ai-ranged  side  by  side, 
represented  as  pear-shaped  black  dots  on  tlie  surface  of  the  newly-fornietl  bone.  the  periosteal 
bone  deposited  in  successive  layers  beneath  the  periosteum  and  en'sheatliing  E.  the  spongy  endochon- 
dral bone;  represented  as  more  deeply  shaded,  u'ithin  the  trabecuhv  of  endochondral  spongy  bone 
are  seen  the  remains  of  the  calcified  cartilage  trabecular  represented  its  dark  wavy  lines.  0.  the  me- 
dulla, with  V,  V,  veins.  In  the  lower  half  of  the  figvu'e  the  endochondral  spongy  bone  has  been  com- 
pletely absorbed.   (Klein  and  Noble  Smith.) 

section  on  '^ossification  in  membrane,"  and  thus  a  casing  of  periosteal 
bone  is  formed  around  the  embryonic  endochondral  spongy  bone:  this 
casing  is  thickest  at  the  centre,  where  it  is  first  formed,  and  thins  out 
toward  each  end  of  the  shaft.  Tlic  embryonic^  si)ongy  bone  is  absorbed, 
its  trabeculas  becoming  gradually  thinned  and  its  meshes  enlarging,  and 
finally  coalescing  into  one  great  cavity — the  medullary  cavity  of  the  shaft. 
Stage  5. — Absorption  of  the  Inner  Layers  of  the  Periosteal 


STRUCTUKE  OF  THE  ELEMENTARY  TISSUES. 


53 


Bone. — The  absorption  of  the  endochondral  spongy  bone  is  now  complete, 
and  the  medullary  cavity  is  bounded  by  periosteal  bone:  the  inner  layers 
of  this  periosteal  bone  are  next  absorbed,  and  the  medullary  cavity  is 
thereby  enlarged,  while  the  deposition  of  bone  beneath  the  periosteum 
continues  as  before.  The  first-formed  periosteal  bone  is  spongy  in  char- 
acter. 

Stage  6. — Formation  of  Compact  Bone. — The  transformation 
of  spongy  periosteal  bone  into  compact  bone  is  effected  in  a  manner 
exactly  similar  to  that  which  has  been  described  in  connection  with  ossi- 
fication in  membrane  (p.  47). 
areolae  in  the  spongy  bone  are 
absorbed,  while  the  osteoblasts 
which  line  them  are  developed 
in  concentric  layers,  each  layer 
in  turn  becoming  ossified  till  the 
comparatively  large  space  in  the 
centre  is  reduced  to  a  well- 
formed  Haversian  canal  (Fig. 
57).  When  once  formed,  bony 
tissue  grows  to  some  extent  in- 
terstitially,  as  is  evidenced  by 
the  fact  that  the  lacunas  are 
rather  further  apart  in  fully- 
formed  than  in  young  bone. 

From  the  foregoing  descrip- 
tion of  the  development  of  bone, 
it  will  be  seen  that  the  common 
terms  ' 'ossification  in  cartilage^' 
and  ' 'ossification  in  membrane'^ 
are  apt  to  mislead,  since  they 
seem  to  imply  two  processes  radi- 
cally distinct.  The  process  of 
ossification,  however,  is  in  all 
cases  one  and  the  same,  all  true  bony  tissue  being  formed  from  membrane 
(perichondrium  or  periosteum);  but  in  the  development  of  such  a  bone 
as  the  femur,  which  may  be  taken  as  the  type  of  so-called  ''ossification  in 
cartilage,"  lime-salts  are  deposited  in  the  cartilage,  and  this  calcified  car- 
tilage is  gradually  and  entirely  re-absorbed,  being  ultimately  replaced  by 
bone  formed  from  the  periosteum,  till  in  the  adult  structure  nothing  but 
true  bone  is  left.  Thus,  in  the  process  of  "ossification  in  cartilage,"  cal- 
cification of  the  cartilaginous  matrix  precedes  the  real  formation  of  bone. 
We  must,  therefore,  clearly  distinguish  between  calcification  and  ossifica- 
tion. The  farmer  is  simply  the  infiltration  of  an  animal  tissue  with 
lime-salts,  and  is,  therefore,  a  change  of  chemical  composition  rather 


The  irregularities  in  the  walls  of  the 


Fig.  57. — Transverse  section  of  femur  of  a  human 
embryo  about  eleven  weeks  old.  a,  rudimentary  Ha- 
versian canal  in  cross  section ;  6,  in  longitudinal  section ; 
c,  osteoblasts ;  ci,  newly  formed  osseous  substance  of  a 
lighter  color ;  e,  that  of  greater  age ;  /,  laeunae  with  their 
cells;     a  cell  still  miited  to  an  osteoblast.  (Frey.) 


54 


HA^s^D-BOOK  OF  PHYSIOLOGY. 


than  of  structure;  while  ossification  is  the  formation  of  true  bone — a 
tissue  more  comr>lex  and  more  liighly  organized  than  that  from  which  it 
is  derived. 

Centres  of  Ossification. — In  all  bones  ossification  commences  at 
one  or  more  points^  termed  "centres  of  ossification.^^  The  long  bones, 
e.g.,  femur,  humerus,  etc.,  have  at  least  three  such  points — one  for  the 
ossification  of  the  shaft  or  diapJiysis,  and  one  for  each  articular  extremity 
or  epipJiysis.  Besides  these  three  primary  centres  which  are  always  pres- 
ent in  long  bones,  various  secondary  centres  may  be  superadded  for  the 
ossification  of  different  ^jroce^^es. 

Growth  of  Bone. — Bones  increase  i?i  length  by  the  advance  of  the 
process  of  ossification  into  the  cartilage  intermediate  between  the  dia- 
physis  and  epiphysis.    The  increase  in  length  indeed  is  due  entirely  to 


Fig.  58.— a.  Longitudinal  section  of  a  human  molar  tooth;  c,  cement;  <7,  dentine;  e,  enamel;  v, 
pulp  cavity.  (Owen.) 

B.  Traiisverse  section.   The  letters  indicate  the  same  as  in  a. 


growth  at  the  two  ends  of  the  shaft.  This  is  proved  by  inserting  two 
pins  into  the  shaft  of  a  growing  bone:  after  some  time  their  distance 
ajDart  will  be  found  to  be  unaltered  though  the  bone  has  gradually  in- 
creased in  length,  the  growth  having  taken  place  beyond  and  not  be- 
tween them.  If  now  one  pin  be  placed  in  the  shaft,  and  the  other  in  the 
epiphysis,  of  a  growing  bone,  their  distance  apart  will  increase  as  the  bone 
grows  in  length. 

Thus  it  is  that  if  the  epiphyses  with  the  intermediate  cartilage  be  re- 
moved from  a  young  bone,  growth  in  length  is  no  longer  possible;  while  tlio 
natural  termination  of  growth  of  a  bone  in  lengtli  takes  place  when  the 
epiphyses  become  united  in  bony  continuity  with  the  shaft. 

Increase  in  thickness  in  the  shaft  of  a  long  bone,  occurs  by  the  depo- 
sition of  successive  layers  beneath  the  periosteum. 

If  a  tliiii  metal  plate  be  Inserted  beneath  the  periosteum  of  a  growing 
bone,  it  will  soon  be  covered  by  osseous  deposit,  but  if  it  be  put  betM-een  the 


STRUCTURE  OF  THE  ELEMENTARY  TISSUES. 


55 


fibrous  and  osteogenetic  layers,  it  will  never  become  enveloijed  in  bone, 
for  all  the  bone  is  formed  beneath  the  latter. 


Other  varieties  of  connective  tissue  may  become  ossified,  e.g. 
tendons  in  some  birds. 


the 


Functions  of  Bones. — Bones  form  the  framework  of  the  body;  for 
this  they  are  fitted  by  their  liardness  and  solidity  together  with  their  com- 
parative lightness;  they  serve  both  to  protect  internal  organs  in  the  trunk 
and  skull,  and  as  levers  worked  by  muscles 
in  the  limbs;  notwithstanding  their  hard- 
ness they  possess  a  considerable  degree  of 
elasticity,  which  often  saves  them  from 
fractures. 

Teeth. 

The  principal  part  of  a  tooth,  viz.,  den- 
tine, is  called  by  some  a  connective  tissue, 
and  on  this  account  the  structure  of  the 
teeth  is  considered  here. 

A  tooth  is  generally  described  as  pos- 
sessing a  crown,  neck,  Sbiid  fang  or  fangs. 

The  C7'0wn  is  the  portion  which  pro- 
jects beyond  the  level  of  the  gum.  The 
neck  is  that  constricted  portion  just  below 
the  crown  w^hich  is  embraced  by  the  free 
edges  of  the  gum,  and  the  fang  includes  all 
below  this. 

On  making  a  longitudinal  section 
through  the  centre  of  a  tooth  (Figs.  58, 
59),  it  is  found  to  be  principally  composed 
of  a  hard  matter,  dentine  or  ivory;  while 
in  the  centre  this  dentine  is  hollowed  out 
into  a  cavity  resembling  in  general  shape 
the  outline  of  the  tooth,  and  called  the 
pulp  cavity,  from  its  containing  a  very  vascular  and  sensitive  little 
mass,  composed  of  connective-tissue,  blood-vessels,  and  nerves,  w^hich  is 
called  the  tooth-pulp. 

The  blood-vessels  and  nerves  enter  the  pulp  through  a  small  opening 
at  the  extremity  of  the  fang. 

Capping  that  part  of  the  dentine  which  projects  beyond  the  level  of 
the  gum,  is  a  layer  of  very  hard  calcareous  matter,  the  enamel;  while 
sheathing  the  portion  of  dentine  which  is  beneath  the  level  of  the  gum, 
is  a  layer  of  true  bone,  called  the  cement  or  crusta  petrosa. 


Fig.  59.— Premolar  tooth  of  cat  in  situ. 
Vertical  section.  1.  Enamel  with  decus- 
sating and  parallel  strige.  2.  Dentine  with 
Schreger's  Unes.  3.  Cement.  4.  Perios- 
teum of  alveolus.  5.  Inferior  maxillary 
bone  showing  canal  for  the  inferior 
dental  nerve  and  vessels  which  appears 
nearly  circular  in  transverse  section. 
(Waldeyer.) 


56 


HAND-BOOK  OF  PHYSIOLOGY. 


At  the  neck  of  the  tooth,  where  the  enamel  and  cement  come  into 
contact,  each  is  reduced  to  an  exceedingly  thin  layer.  The  covering  of 
enamel  becomes  thicker  as  we  approach  the  crown,  and  the  cement  as  we 
approach  the  lower  end  or  apex  of  the  fang. 

I. — Dentine. 

Chemical  composition. — Dentine  or  ivory  in  chemical  composition 
closely  resembles  bone.  It  contains,  however,  rather  less  animal  matter; 
the  proportion  in  a  hundred  parts  being  about  twenty-eight  animal  to 
seventy-two  of  earthy.  The  former,  like  the  animal  matter  of  bone,  may 
be  resolved  into  gelatin  by  boiling.  The  earthy  matter  is  made  up  chiefly 
of  calcium  phosphate,  with  a  small  portion  of  the  carbonate,  and  traces 
of  calcium  fluoride  and  magnesium  phosphate. 

Structure. — Under  the  microscope  dentine  is  seen  to  be  finely  chan- 
neled by  a  multitude  of  delicate  tubes,  which,  by  their  inner  ends,  com- 


FiG.  60.— Section  of  a  portion  of  the  dentine  and  cement  from  the  middle  of  the  root  of  an  incisor 
tooth,  a,  dental  tubuU  ramifying  and  terminating,  some  of  them  in  the  interglobular  spaces  6  and  c, 
which  somewhat  resemble  bone  lacunae;  d,  inner  layer  of  the  cement  with  numerous  closely  set 
canahculi;  e,  outer  layer  of  cement;  /,  lacunae;  (/,  canalicuh.    x  350.  (KoUiker.) 

municate  with  the  pulp-cavity,  and  by  their  outer  extremities  come  into 
contact  with  the  under  part  of  the  enamel  and  cement  and  sometimes 
even  penetrate  them  for  a  greater  or  less  distance  (Fig.  60). 

In  their  course  from  the  pulp-cavity  to  the  surface  of  the  dentine,  the 
minute  tubes  form  gentle  and  nearly  parallel  curves  and  divide  and  sub- 
divide dichotomously,  but  without  much  lessening  of  their  calibre  until 
they  are  approaching  their  peripheral  termination. 

From  their  sides  proceed  other  exceedingly  minute  secondary  canals, 
which  extend  into  the  dentine  between  the  tubules,  and  anastomose  with 
eacli  other.  The  tubules  of  the  dentine,  the  average  diameter  of  whicli 
at  tlieir  inner  and  larger  extremity  is  of  an  inch,  contain  line  pro- 
longations from  the  tootli-pul]),  which  give  the  dentine  a  certain  faint 
sensitiveness  under  ordinary  circumstances,  and,  without  doubt,  have  to 
do  also  with  its  nutrition.  These  i)r()longations  from  the  tooth-pulp  are 
really  processes  of  the  dentine-cells  or  odontoblasts  which  arc  branched  cells 
lining  the  ])iili)-cavity;  the  relation  of  these  processes  to  the  tubules' in 


STRUCTURE  OF  THE  ELEMENTARY  TISSUES. 


57 


which  they  lie  being  precisely  similar  to  that  of  the  processes  of  the  bone- 
corpuscles  to  the  canaliculi  of  bone.  The  outer  portion  of  the  dentine, 
underlying  both  the  cement  and  enamel,  forms  a  more  or  less  distinct 
layer  termed  the  granular  or  inter  globular  layer.  It  is  characterized  by 
the  presence  of  a  number  of  minute  cell-like  cavities,  much  more  closely 
packed  than  the  lacunae  in  the  cement,  and  communicating  with  one 
another  and  with  the  ends  of  the  dentine-tubes  (Fig.  60),  and  containing 
cells  like  bone-corpuscles. 

II. — Enamel, 

Chemical  composition. — The  enamel,  which  is  by  far  the  hardest  por- 
tion of  a  tooth,  is  composed,  chemically,  of  the  same  elements  that  enter 


Fig.  61.  Fxg.  C2. 


Fig.  61.— Thin  section  of  the  enamel  and  a  part  of  the  dentine,  a,  cuticular  pellicle  of  the  enamel; 
b,  enamel  fibres,  or  columns  with  fissures  between  them  and  cross  striae ;  c,  larger  cavities  in  the 
enamel,  communicating  with  the  extremities  of  some  of  the  tubuli  {d).    X  350.  (KoUilser.) 

Fig.  62.— Enamel  fibres.  A,  fragments  and  single  fibres  of  the  enamel,  isolated  by  the  action  of 
hydrochloric  acid.  B,  surface  of  a  smaU  fragment  of  enamel,  showing  the  hexagonal  ends  of  the 
fibres.    X  350.  (KoUiker.) 

into  the  composition  of  dentine  and  bone.  Its  animal  matter,  however, 
amounts  only  to  about  2  or  3  per  cent.  It  contains  a  larger  proportion  of 
inorganic  matter  and  is  harder  than  any  other  tissue  in  the  body. 

Structure. — Examined  under  the  microscope,  enamel  is  found  com- 
posed of  fine  hexagonal  fibres  (Figs.  61,  62)  y^Vo  diameter. 


58 


HA^^D-BOOK  OF  PHYSIOLOGY. 


which  are  set  on  end  on  the  surface  of  the  dentine,  and  fit  into  corre- 
sponding depressions  in  the  same. 

They  radiate  in  such  a  manner  from  the  dentine  that  at  the  top  of  the 
tooth  they  are  more  or  less  vertical,  while  toward  the  sides  they  tend  to 
the  horizontal  direction.  Like  the  dentine  tubules,  they  are  not  straight, 
but  disposed  in  wavy  and  parallel  curves.    The  fibres  are  marked  by 

transverse  lines,  and  are  mostly 
solid,  but  some  of  them  contain  a 
very  minute  canal. 

The  enamel-prisms  are  con- 
nected together  by  a  very  minute 
quantity  of  hyaline  cement-sub- 
stance. In  the  deeper  part  of  the 
enamel,  between  the  prisms,  are 
small  lacuncB,  which  communicate 
with  the  ^^interglobular  spaces" 
on  the  surface  of  the  dentine. 

The  enamel  itself  is  coated  on 
the  outside  by  a  very  thin  calci- 
fied membrane,  sometimes  termed 
the  cuticle  of  the  enamel. 


III. — Crusta  Petrosa. 

The  crusta  petrosa,  or  cement 
(Fig.  60,  c,  d),  is  composed  of  true 
bone,  and  in  it  are  lacuna  (/ )  and 
canaliculi  (g)  which  sometimes 
communicate  with  the  outer  fine- 
ly branched  ends  of  the  dentine 
tubules.  Its  lamina  are  as  it  were 
bolted  together  by  perforating 
fibres  like  those  of  ordinary  bone, 
but  it  differs  in  possessing  Haver- 
sian canals  only  in  the  thickest 
part. 

Development  of  Teeth. 


Fig.  63.— Section  of  the  upper  jaAv  of  a  foetal  sheep. 
A.— 1,  common  enamel-t^erm  dipping  down  into  the 
mucous  membrane;  2,  palatine  jn-oeess  of  jaw.  B.— 
Section  similar  to  A,  but  passing  through  one  of  the 
special  enamel-germs  hen"  becoming  fhisk-shapcd;  c, 
c',  epithelium  of  mouth;  /,  neck;  /',  InuU  of  special 
enamel-germ.  C— A  later  st  age ;  r  ,  on 1 1  ine  of  cpi 1 1  le- 
lium  of  gum;  /,  neck  of  enamel-germ;  /',  enamel 
organ;  papilla;  s,  dental  sax;  forming;  f  j>,  the 
enamel-germ  of  permanent  tooth.  (Waldeyer  and 
KoUiker.)  Copied  from  Quaiu's  Anatomy. 


Development  of  the  Teeth. — The 
first  step  in  the  development  of  the 
teeth  consists  in  a  downward  growtli  (Fig.  G3,  A,  1)  from  tlie  stratified 
epithelium  of  the  mucous  membrane  of  the  mouth,  now  thickened  in  tlie 
neiglil)orliood  of  the  miixilla3  wliich  are  in  the  course  of  formation.  This 
process  i)asses  downward  into  a  recess  (enamel  groove)  of  the  imperfectly 
developed  tissue  of  which  the  chief  part  of  tb 


jaw  consists.    The  down- 


STKUCTUKE  OF  THE  ELEMENTARY  TISSUES. 


59 


ward  epithelial  growth  forms  the  primary  enmnd  organ  or  enamel  germ, 
and  its  position  is  indicated  by  a  slight  groove  in  the  mucous  membrane 
of  the  jaw.  The  next  step  in  the  process  consists  in  the  elongation  down- 
ward of  the  enamel  groove  and  of  the  enamel  germ  and  the  inclination 
outward  of  the  deeper  part  (Fig.  63,  b,  which  is  now  inclined  at  an 
angle  with  the  upper  portion  or  neck  (/),  and  has  become  bulbous.  After 
this,  there  is  an  increased  development  at  certain  points  corresponding 
to  the  situations  of  the  future  milk-  teeth,  and  the  enamel  germ,  or  com- 
mon enamel  germ,  as  it  may  be  called,  becomes  divided  at  its  deeper  por- 
tion, or  extended  by  further  growth,  into  a  number  of  special  enamel 
germs  corresponding  to  each  of  the  above-mentioned  milk  teeth,  and  con- 
nected to  the  common  germ  by  a  narrow  neck,  each  tooth  being  placed 
in  its  own  special  recess  in  the  embryonic  jaw  (Fig.  63,  b,//'). 

As  these  changes  proceed,  there  grows  up  from  the  underlying  tissue 
into  each  enamel  germ  (Fig.  63,  c,  jo),  a  distinct  vascular  papilla  (dental 
papilla),  and  upon  it  the  enamel  germ 
becomes  moulded  and  presents  the  ap- 
pearance of  a  cap  of  two  layers  of  epi- 
thelium separated  by  an  interval  (Fig. 
63,  c,  /).  Whilst  part  of  the  sub- 
epithelial tissue  is  elevated  to  form  the 
dental  papillae,  the  part  which  bounds 
the  embryonic  teeth  forms  the  dental 
sacs  (Fig.  63,  c,  s);  and  the  rudiment 
of  the  jaw,  at  first  a  bony  gutter  in 
which  the  teeth  germs  lie,  sends  up 
processes  forming  partitions  between 
the  teeth.  In  this  way  small  chambers 
are  produced  in  which  the  dental  sacs  are 
contained,  and  thus  the  sockets  of  the 
teeth  are  formed.  The  papilla,  which  is  really  part  of  the  dental  sac,  if 
one  thinks  of  this  as  the  whole  of  the  sub-epithelial  tissue  surrounding  the 
enamel  organ  and  interposed  between  the  enamel  germ  and  the  develop- 
ing bony  jaw,  is  composed  of  nucleated  cells  arranged  in  a  meshwwk,  the 
outer  or  peripheral  part  being  covered  with  a  layer  of  columnar  nucleated 
cells  called  odontoblasts.  The  odontoblasts  form  the  dentine,  while  the 
remainder  of  the  papilla  forms  the  tooth-pulp.  The  method  of  the  for- 
mation of  the  dentine  from  the  odontoblasts  is  as  follows: — The  cells  elon- 
gate at  their  outer  part,  and  these  processes  are  directly  converted  into 
the  tubules  of  dentine  (Fig.  64).  The  continued  formation  of  dentine 
proceeds  by  the  elongation  of  the  odontoblasts,  and  their  subsequent  con- 
version by  a  process  of  calcification  into  dentine  tubules.  The  most 
recently  formed  tubules  are  not  immediately  calcified.  The  dentine  fibres 
contained  in  the  tubules  are  said  to  be  formed  from  processes  of  the 


Fig.  64.— Part  of  section  of  developing  tooth 
of  a  young  rat,  showing  the  mode  of  deposi- 
tion of  the  dentine.  Highly  magnified,  a, 
outer  layer  of  fully  formed  dentine ;  6,  uncal- 
cified  matrix  with  one  or  tM^o  nodules  of  cal- 
careous matter  near  the  calcified  parts;  c, 
odontoblasts  sending  processes  into  the  den- 
tine; d,  pulp.  The  section  is  stained  in  car- 
mine, which  colors  the  uncalcified  matrix  but 
not  the  calcified  part.   (E.  A.  Schafer.) 


60 


HAND-BOOK  OF  PHYSIOLOGY. 


deeper  layer  of  odontoblasts,  which  are  wedged  in  between  the  cells  of 
the  superficial  layer  (Fig.  64)  which  form  the  tubules  only. 

Since  the  papillae  are  to  form  the  main  portion  of  each  tooth,  i.e.,  the 
dentine,  each  of  them  early  takes  the  shape  of  the  crown  of  the  tooth  it  is 
to  form.  As  the  dentine  increases  in  thickness,  the  papillae  diminish, 
and  at  last  when  the  tooth  is  cut,  only  a  small  amount  of  the  papilla 
remains  as  the  dental  pulp,  and  is  supplied  by  vessels  and  nerves  which 
enter  at  the  end  of  the  fang.  The  shape  of  the  crown  of  the  tooth  is 
taken  by  the  corresponding  papilla,  and  that  of  the  single  or  double  fang 

by  the  subsequent  constriction  be- 
low the  crown,  or  by  division  of  the 
lower  part  of  the  papilla. 

The  enamel  cap  is  found  later  on 
to  consist  (Fig.  65)  of  three  parts: 
{a)  an  inner  membrane,  composed 
of  a  layer  of  columnar  epithelium  in 
contact  with  the  dentine,  called  ena- 
mel cells,  and  outside  of  these  one  or 
more  layers  of  small  polyhedral  nu- 
cleated cells  (stratum  intermedium 
of  Hannover);  {b)  an  outer  mem- 
brane of  several  layers  of  epithelium; 
(c)  a  middle  membrane  formed  of  a 
matrix  of  non-vascular,  gelatinous 
tissue,  containing  a  hyaline  intersti- 
tial substance.  The  enamel  is  formed 
by  the  enamel  cells  of  the  inner 
membrane,  by  the  elongation  of 
their  distal  extremities,  and  the  di- 
rect conversion  of  these  processes 
into  enamel.  The  calcification  of 
the  enamel  processes  or  prisms  take? 
place  first  at  the  periphery,  the  cen- 
tre remaining  for  a  time  transparent.  The  cells  of  the  stratum  interme- 
dium are  used  for  the  regeneration  of  the  enamel  cells,  but  these  and 
the  middle  membrane  after  a  time  disappear.  The  cells  of  the  outer 
membrane  give  origin  to  the  cuticle  of  the  enamel. 

The  cement  or  crusta  j)etrosa  is  formed  from  the  tissue  of  the  tooth 
sac,  the  structure  and  function  of  which  are  identical  with  those  of  the 
ostcogenctic  layer  of  tlie  periosteum. 

In  this  manner  tlio  first  set  of  teeth,  or  the  milk-tectli,  are  formed; 
and  each  tooth,  by  degrees  developing,  presses  at  length  on  the  wall  of  the 
sac  enclosing  it,  and,  causing  its  absorjition,  is  cut,  to  use  a  familiar  phrase. 
The  teinporary  ov  milk-teeth  have  only  a  very  limited  term  of  existence. 


Fig.  65.— Vertical  transverse  section  of  the 
dental  sac,  pulp,  etc.,  of  a  kitten,  a,  dental 
papilla  or  pulp;  6,  the  cap  of  dentine  formed 
upon  the  summit;  c,  its  covering  of  enamel;  d, 
inner  layer  of  epithelium  of  the  enamel  organ;  e, 
gelatinous  tissue ;  /,  outer  epithelial  layer  of  the 
enamel  organ;  g,  inner  layer,  and  h,  outer  layer 
of  dental  sac.    X  14.  (Thiersch.) 


STRUCTURE  OF  THE  ELEMENTARY  TISSUES. 


61 


This  is  due  to  the  growth  of  the  permanent  teeth,  which  push  their  way 
up  from  beneath,  absorbing  in  their  progress  the  whole  of  the  fang  of  each 
milk-tooth  and  leaving  at  length  only  the  crown  as  a  mere  shell,  which 
is  shed  to  make  way  for  the  eruption  of  the  permanent  teeth  (Fig.  66). 

The  temporary  teeth  are  ten  in  each  jaw,  namely,  four  incisors,  two 
canines,  and  four  molars,  and  are  replaced  by  ten  permanent  teeth,  each 
of  which  is  developed  in  a  way  almost  exactly  similar  to  the  manner  of 
development  already  described,  from  a  small  process  or  sac  set  by,  so  to 
speak,  from  the  enamel  germ  of  the  temporary  tooth  which  precedes  it, 
and  called  the  cavity  of  reserve. 

The  number  of  permanent  teeth  in  each  jaw  is,  however,  increased  to  six- 
teen, by  the  development  of  three  others  on  each  side  of  the  jaw  after  much 
the  same  fashion  as  that  by  which  the  milk-teeth  were  themselves  formed. 


Fig.  66. — Part  of  the  lower  jaw  of  a  child  of  three  or  four  years  old,  showing  the  relations  of  the 
temporary  and  permanent  teeth.  The  specimen  contains  all  the  milk  teeth  of  the  right  side,  to- 
gether with  the  incisors  of  the  left;  the  inner  plate  of  the  jaw  has  been  removed,  so  as  to  expose  the 
sacs  of  all  the  permanent  teeth  of  the  right  side,  except  the  eighth  or  wisdom  tooth,  which  is  not  yet 
formed.  The  large  sac  near  the  ascending  ramus  of  the  jaw  is  that  of  the  first  permanent  molar,  and 
above  and  behind  it  is  the  commencing  rudiment  of  the  second  molar.  (Quain.) 


The  beginning  of  the  development  of  the  permanent  teeth  of  course 
takes  place  long  before  the  cutting  of  those  which  they  are  to  succeed. 
One  of  the  first  steps  in  the  development  of  a  milk-tooth  is  the  out- 
growth of  a  lateral  process  of  epithelial  cells  from  its  primitive  enamel 
organ  (Fig.  63,  c,  f  p).  This  epithelial  outgrowth  ultimately  becomes 
the  enamel  organ  of  the  permanent  tooth,  and  is  indented  from  below  by 
a  primitive  dental  papilla,  precisely  as  described  above. 

The  following  formula  shows,  at  a  glance,  the  comparative  arrange- 
ment and  number  of  the  temporary  and  permanent  teeth: — 


Temporary  Teeth 


Permanent  Teeth 


Mo.  Bi.  Ca.  In.  Ca.  Bi.  Mo. 
Upper    3    2    1    4    1    2  3=16 


=32 


Lower    3    2    1    4    1    2    3  =  16 


62 


HAND-BOOK  OF  PHYSIOLOGY. 


From  this  formula  it  will  be  seen  that  the  two  bicuspid  teeth  in  the 
adult  are  the  successors  of  the  two  molars  in  the  child.  They  differ  from 
them,  however,  in  some  respects,  the  temporary  molars  having  a  stronger 
likeness  to  the  permanent  than  to  their  immediate  descendants,  the  so- 
called  bicuspids. 

The  temporary  incisors  and  canines  differ  from  their  successors  but 
little  except  in  their  smaller  size. 

The  following  tables  show  the  average  times  of  eruption  of  the  Tem- 
porary and  Permanent  teeth.  In  both  cases,  the  eruption  of  any  given 
tooth  of  the  lower  jaw  precedes,  as  a  rule,  that  of  the  corresponding  tooth 
of  the  upper. 

Temporary  or  MilJc  Teeth. 
The  figures  indicate  in  months  the  age  at  which  eacQ  tooth  appears. 


Molars.  Canines,  Incisors.  Canines.  Molars. 


24  12 


18 


9  7  7  9 


18 


12  24 


Permanent  Teeth. 
The  age  at  which  each  tooth  is  cut  is  indicated  in  this  table  in  years. 


Molars. 

Bicuspid. 

Canines. 

Incisors. 

Canines. 

Bicuspid. 

Molars. 

17  12 

to    to  6 
25  13 

10  9 

11  to  12 

8  7  7  8 

11  to  12 

9  10 

12  17 
6  to  to 

13  25 

The  times  of  eruption  put  down  in  the  above  tables  are  only  approxi- 
mate: the  limits  of  variation  being  tolerably  wide.  Some  children  may 
cut  their  first  teeth  before  the  age  of  six  months,  and  others  not  till  nearly 
the  twelfth  month.  In  nearly  all  cases  the  two  central  incisors  of  the 
lower  jaw  are  cut  first;  these  being  succeeded  after  a  short  interval  by  the 
four  incisors  of  the  upper  jaw,  next  follow  the  lateral  incisors  of  the  lower 
jaw,  and  so  on  as  indicated  in  the  table  till  the  completion  of  the  milk 
dentition  at  about  the  age  of  two  years. 

The  milk-teeth  usually  come  through  in  batches,  each  period  of  erup- 
tion being  succeeded  by  one  of  quiescence  lasting  sometimes  several 
months.  The  milk-teeth  are  in  use  from  the  age  of  two  up  to  five  and  a 
half  years:  at  about  this  age  the  first  permanent  molars  (four  in  number) 
make  their  appearance  behind  the  milk-molars,  and  for  a  short  time  the 
child  has  four  permanent  and  twenty  temporary  teeth  in  position  at  once. 

It  is  worthy  of  iiotc^  tliat  from  the  age  of.  five  years  to  the  shedding  of 
the  first  milk-tootli  the  child  has  no  fewer  than  forty-eight  teeth,  twenty 
milk-teeth  and  twenty-eight  calcified  germs  of  permanent  teeth  (all  in 
fact  except  the  four  wisdom  teeth). 


CHAPTER  IV. 


THE  BLOOD. 

The  blood  of  man,  as  indeed  of  the  great  majority  of  vertebrate  ani- 
mals, is  a  more  or  less  viscid  fluid,  of  a  red  color.  The  exact  shade  of 
red  is  variable,  for  whereas  that  taken  from  the  arteries,  from  the  left 
side  of  the  heart  or  from  the  pulmonary  veins,  is  of  a  bright  scarlet  hue, 
that  obtained  from  the  systemic  veins,  from  the  right  side  of  the  heart, 
or  from  the  pulmonary  artery,  is  of  a  much  darker  color,  and  varies  from 
bluish-red  to  reddish-black.  To  the  naked  eye,  the  red  color  appears  to 
belong  to  the  whole  mass  of  blood,  but  on  examination  with  the  micro- 
scope it  is  found  that  this  is  not  the  case.  By  the  aid  of  this  instrument 
the  blood  is  shown  to  consist  in  reality  of  an  almost  colorless  fluid,  called 
Liquor  Sanguinis  or  Plasma,  in  which  are  suspended  numerous  minute 
rounded  masses  of  protoplasm,  called  Blood  Corpuscles.  The  corpuscles 
are,  for  the  most  part,  colored,  and  it  is  to  their  presence  that  the  red 
color  of  the  blood  is  due. 

Even  when  examined  in  very  thin  layers  blood  is  opaque,  on  account 
of  the  different  refractive  powers  possessed  by  its  two  constituents,  viz., 
the  plasma  and  the  corpuscles.  On  treatment  with  chloroform  and  other 
reagents,  however,  it  becomes  transparent,  and  assumes  a  lake  color,  in 
consequence  of  the  coloring  matter  of  the  corpuscles  having  been,  by 
these  means,  discharged  into  the  plasma.  The  average  specific  gravity  of 
blood  at  60°  F.  (15°  0.)  is  1055,  the  extremes  consistent  with  health 
being  1045-1062.  The  reaction  of  blood  is  faintly  alkaline.  Its  temper- 
ature varies  within  narrow  limits,  the  average  being  100°  F.  (37*8°  C). 
The  blood  stream  is  slightly  warmed  by  passing  through  the  muscles, 
nerve  centres,  and  glands,  but  is  somewhat  cooled  on  traversing  the  capil- 
laries of  the  skin.  Eecently  drawn  blood  has  a  distinct  odor,  which  in 
many  cases  is  characteristic  of  the  animal  from  which  it  has  been 
taken;  the  odor  may  be  further  developed  by  adding  to  blood  a  mixture 
of  equal  parts  of  sulphuric  acid  and  water. 

Quantity  of  the  Blood. — The  quantity  of  blood  in  any  animal  under 
normal  conditions  bears  a  pretty  constant  relation  to  the  body  weight. 
The  methods  employed  for  estimating  it  are  not  so  simple  as  might  at 
first  sight  be  thought.  For  example,  it  would  not  be  possible  to  get  any 
accurate  information  on  the  point  from  the  amount  obtained  by  rapidly 


64 


HAND-BOOK  OF  PHYSIOLOGY. 


bleeding  an  animal  to  death,  for  then  an  indefinite  quantity  would  remain 
in  the  vessels,  as  well  as  in  the  tissues;  nor,  on  the  other  hand,  would  it 
be  possible  to  obtain  a  correct  estimate  by  less  rapid  bleeding,  as,  since  life 
would  be  more  prolonged,  time  would  be  allowed  for  the  passage  into  the 
blood  of  lymph  from  the  lymphatic  vessels  and  from  the  tissues.  In  the 
former  case,  therefore,  we  should  under-estimate,  and  in  the  latter  over- 
estimate the  total  amount  of  the  blood. 

Of  the  several  methods  which  have  been  employed,  the  most  accurate 
appears  to  be  the  following.  A  small  quantity  of  blood  is  taken  from  an 
animal  by  venesection;  it  is  defibrinated  and  measured,  and  used  to  make 
standard  solutions  of  blood.  The  animal  is  then  rapidly  bled  to  death, 
and  the  blood  which  escapes  is  collected.  The  blood-vessels  are  next 
washed  out  with  water  or  saline  solution  until  the  washings  are  no  longer 
colored,  and  these  are  added  to  the  previously  withdrawn  blood;  lastly 
the  whole  animal  is  finely  minced  with  water  or  saline  solution.  The 
fluid  obtained  from  the  mincings  is  carefully  filtered,  and  added  to  the 
diluted  blood  previously  obtained,  and  the  whole  is  measured.  Ths 
next  step  in  the  process  is  the  comparison  of  the  color  of  the  diluted  blood 
with  that  of  standard  solutions  of  blood  and  water  of  a  known  strength, 
until  it  is  discovered  to  what  standard  solution  the  diluted  blood  corre- 
sponds. As  the  amount  of  blood  in  the  corresponding  standard  solution 
is  known,  as  well  as  the  total  quantity  of  diluted  blood  obtained  from  the 
animal,  it  is  easy  to  calculate  the  absolute  amount  of  blood  which  the 
latter  contained,  and  to  this  is  added  the  small  amount  which  was  with- 
drawn  to  make  the  standard  solutions.  This  gives  the  total  amount  of 
blood  which  the  animal  contained.  It  is  contrasted  with  the  weight  of 
the  animal,  previously  known.  The  result  of  many  experiments  shows 
that  the  quantity  of  blood  in  various  animals  averages  -^j  to  of  the 
total  body  weight. 

An  estimate  of  the  quantity  in  man  which  corresponded  nearly  with 
the  above,  was  made  some  years  ago  from  the  following  data.  A  crim- 
inal was  weighed  before  and  after  decapitation;  the  difference  in  the 
weight  representing,  of  course,  the  quantity  of  blood  which  escaped. 
The  blood-vessels  of  the  head  and  trunk  were  then  washed  out  by  the  in- 
jection of  water,  until  the  fluid  which  escaped  had  only  a  pale  red  or  straw 
color.  This  fluid  was  then  also  weighed;  and  the  amount  of  blood  which 
it  represented  was  calculated  by  comparing  the  proportion  of  solid  matter 
contained  in  it  with  tliat  of  the  first  blood  which  escaped  on  decapitation. 
Two  experiments  of  this  kind  gave  precisely  similar  results.  (Weber  and 
Lehmann.) 

It  should  1)0  remembered,  however,  in  connection  with  these  estima- 
tions, that  the  quantity  of  the  blood  must  vary,  even  in  the  same  animal, 
very  (considerably  with  the  amount  of  both  the  ingesta  and  egesta  of  the 
period  inunctl lately  preceding  the  experiment;  and  it  has  been  found. 


THE  BLOOD. 


65 


indeed,  that  the  quantity  of  blood  obtainable  from  a  fasting  animal  barely 
exceeds  a  half  of  that  which  is  present  soon  after  a  full  meal. 

Coagulation  of  the  Blood. — One  of  the  most  characteristic  proper- 
ties which  the  blood  possesses  is  that  of  clotting  or  coagulating,  when 
removed  from  the  body.  This  phenomenon  may  be  observed  under  the 
most  favorable  conditions  in  blood  which  has  been  drawn  into  an  open 
vessel.  In  about  two  or  three  minutes,  at  the  ordinary  temperature  of 
the  air,  the  surface  of  the  fluid  is  seen  to  become  semi-solid  or  jelly-like; 
this  change  next  taking  place,  in  a  minute  or  two,  at  the  sides  of  the 
vessel  in  which  it  is  contained,  and  then  extending  throughout  the  entire 
mass. 

The  time  which  is  required  for  the  blood  to  become  solid  is  about  eight 
or  nine  minutes.  The  solid  mass  occupies  exactly  the  same  volume  as  the 
previously  liquid  blood,  and  adheres  so  closely  to  the  sides  of  the  contain- 


Fio.  67.— Reticulum  of  fibrin,  from  a  drop  of  human  blood,  after  treatment  with  rosanilin. 

(Ranvler.) 

ing  vessel  that  if  it  be  inverted  none  of  its  contents  escape.  The  solid 
mass  is  the  crassamentum  or  clot.  If  the  clot  be  watched  for  a  few  min- 
utes, drops  of  a  light  straw-colored  fluid,  the  serum,  may  be  seen  to  make 
their  appearance  on  the  surface,  and,  as  they  become  more  and  more  nu- 
merous, run  together,  forming  a  complete  superficial  stratum  above  the 
solid  clot.  At  the  same  time  the  fluid  begins  to  transude  at  the  sides  and 
at  the  under  surface  of  the  clot,  which  in  the  course  of  an  hour  or  two 
floats  in  the  liquid.  The  first  drops  of  serum  appear  on  the  surface  about 
eleven  or  twelve  minutes  after  the  blood  has  been  drawn;  and  the  fluid 
continues  to  transude  for  from  thirty-six  to  forty-eight  hours. 

The  clotting  of  blood  is  due  to  the  development  in  it  of  a  substance 
called  fihHn,  which  appears  as  a  meshwork  (Fig.  67)  of  fine  fibrils.  This 
meshwork  entangles  and  encloses  within  it  the  blood  corpuscles,  as  clot- 
ting takes  place  too  quickly  to  allow  them  to  sink  to  the  bottom  of  the 
plasma.  The  first  clot  formed,  therefore,  includes  the  whole  of  the  con- 
VoL.  I.— 5. 


66 


HAND-BOOK  OF  PHYSIOLOGY. 


stituents  of  the  blood  in  an  apparently  solid  mass,  but  soon  the  fibrinous 
meshwork  begins  to  contract,  and  the  serum  which  does  not  belong  to  the 
clot  is  squeezed  out.  When  the  whole  of  the  serum  has  transuded,  the 
clot  is  found  to  be  smaller,  but  firmer  and  harder,  as  it  is  now  made  up 
of  fibrin  and  blood  corpuscles  only.  It  will  be  noticed  that  coagulation 
rearranges  the  constituents  of  the  blood  according  to  the  following  scheme, 
liquid  blood  being  made  up  of  plasma  and  blood-corpuscles,  and  clotted 
blood  of  serum  and  clot. 


Liquid  Blood. 


Plasma 


Corpuscles 


Serum 


Fibria 


Clot 


Clotted  Blood 


Buffy  Coat. — Under  ordinary  circumstances  coagulation  occurs,  as 
we  have  mentioned  above,  before  the  red  corpuscles  have  had  time  to  sub- 
side; and  thus  from  their  being  entangled  in  the  meshes  of  the  fibrin,  the 
clot  is  of  a  deep  red  color  throughout,  somewhat  darker,  it  may  be,  at  the 
most  dependent  part,  from  accumulation  of  red  corpuscles,  but  not  to  any 
very  marked  degree.  When,  however,  coagulation  is  delayed  from  any 
cause,  as  when  blood  is  kept  at  a  temperature  of  32°  F.  (0°  C),  or  when 
clotting  is  normally  a  slow  process,  as  in  the  case  of  horse^s  blood,  or, 
lastly,  in  certain  diseased  conditions  of  the  blood  in  which  clotting  is 
naturally  delayed,  time  is  allowed  for  the  colored  corpuscles  to  sink  to  the 
bottom  of  the  fluid.  When  clotting  does  occur,  the  upper  layers  of  the 
blood,  being  free  of  colored  corpuscles  and  consisting  chiefly  of  fibrin, 
form  a  superficial  stratum  differing  in  appearance  from  the  rest  of  the 
clot,  in  that  it  is  of  a  grayish  yellow  color.  This  is  known  as  the  huffy 
coat." 

Cupped  appearance  of  the  Clot. — When  the  buffy  coat  has  been 
produced  in  the  manner  just  described,  it  commonly  contracts  more  than 
the  rest  of  the  clot,  on  account  of  the  absence  of  colored  corpuscles  from 
its  meshes,  and  because  contraction  is  less  interfered  with  by  adliesion  to 
the  interior  of  tlic  containing  vessel  in  the  vertical  than  the  horizontal 
direction.  This  produces  a  cup-like  appearance  of  the  buffy  coat,  and  the 
clot  is  not  only  buffed  but  cupped  on  the  surface.  The  bulled  and  cu]>ped 
appearance  of  the  clot  is  well  marked  in  certain  states  of  the  system, 
especially  in  inflammation,  where  the  fibrin-forming  constituents  tu'c  in 
ex(^(\sH,  and  it  is  also  well  marked  in  chlorosis  where  the  corpuscles  are 
deficient  in  quantity. 


THE  BLOOD. 


Formation  of  Fibrin. — In  describing  the  coagulation  of  the  blood  in 

the  preceding  paragraplis^  it  was  stated  that  this  ];)henomenon  was  duo  to 
the  development  in  the  clotting  blood  of  a  meshwork  of  fibrin.  Thin  may 
be  demonstrated  by  taking  recently-drawn  blood,  and  whipping  it  with  a 
bundle  of  twigs;  the  fibrin  is  found  to  adhere  to  the  twigs  as  a  reddish- 
white,  stringy  mass,  having  been  thus  obtained  from  the  fluid  nearly  free 
from  colored  corpuscles.  The  defibrinated  blood  no  longer  retains  the 
power  of  spontaneous  coagulability. 

The  fibrin  which  makes  its  appearance  in  the  blood  when  it  is  under- 
going coagulation  is  derived  chiefly,  if  not  entirely,  from  the  plasma  or 
liquor  sanguinis;  for  although  the  colorless  corpuscles  are  intimately  con- 
nected with  the  process  in  a  way  which  will  be  presently  explained,  the 
colored  corpuscles  appear  to  take  no  active  part  in  it  whatever.  This 
may  be  shown  by  experimenting  with  plasma  free  from  colored  corpuscles. 
Such  plasma  may  be  procured  by  delaying  coagulation  in  blood,  by  keep- 
ing it  at  a  low  temperature,  32°  F.  (0°  C),  until  the  colored  corpuscles 
which  are  of  higher  specific  gravity  than  the  other  constituents  of  blood, 
have  had  time  to  sink  to  the  bottom  of  the  containing  vessel,  and  to  leave 
an  upper  stratum  of  colorless  plasma,  in  the  lower  layers  of  which  are 
many  colorless  corpuscles.  The  blood  of  the  horse  is  specially  suited  for 
the  purposes  of  this  experiment;  and  the  upper  stratum  of  colorless 
plasma  derived  from  it,  if  decanted  into  another  vessel  and  exposed  to  the 
ordinary  temperature  of  the  air,  will  coagulate  just  as  though  it  were  the 
entire  blood,  producing  a  clot  similar  in  all  respects  to  blood  clot,  except 
that  it  is  almost  colorless  from  the  absence  of  red  corpuscles.  If  some  of 
the  plasma  be  diluted  with  neutral  saline  solution,'  coagulation  is  de- 
layed, and  the  stages  of  the  gradual  formation  of  fibrin  may  be  more  con- 
veniently watched.  The  viscidity  which  precedes  the  complete  coagula- 
tion may  be  seen  to  be  due  to  fibrin  fibrils  developing  in  the  fluid — first 
of  all  at  the  circumference  of  the  containing  vessel,  and  gradually  extend- 
ing throughout  the  mass.  Again,  if  plasma  be  whipped  with  a  bundle  of 
twigs,  the  fibrin  may  be  obtained  as  a  solid,  stringy  mass,  just  in  the 
same  way  as  from  the  entire  blood,  and  the  resulting  fluid  no  longer 
retains  its  power  of  spontaneous  coagulability.  Evidently,  therefore, 
fibrin  is  derived  from  the  plasma  and  not  from  the  colored  corpuscles. 
In  these  experiments,  it  is  not  necessary  that  the  plasma  shall  have  been  ob- 
tained by  the  process  of  cooling  above  described,  as  plasma  obtained  in 
any  other  way,  e.g.,  by  allowing  blood  to  flow  direct  from  the  vessels  of 
an  animal  into  a  vessel  containing  a  third  or  a  fourth  of  the  bulk  of  the 
blood  of  a  saturated  solution  of  a  neutral  salt  (preferably  of  magnesium 
sulphate)  and  mixing  carefully,  will  answer  the  purpose,  and,  just  as  in 
the  other  case,  the  colored  corpuscles  will  subside,  leaving  the  clear  super- 

^  Neutral  saline  solution  commonly  consists  of  a  '75  solution  of  common  salt 
(sodium  chloride)  in  water. 


68 


HAKD-BOOK  OF  PHYSIOLOGY. 


stratum  of  (salted)  plasma.  In  order  to  cause  this  plasma  to  coagulate, 
it  is  necessary  to  get  rid  of  the  salts  by  dialysis,  or  to  dilute  it  with  several 
times  its  bulk  of  water. 

The  antecedent  of  Fibrin. — If  plasma  be  saturated  with  solid 
magnesium  sulphate  or  sodium  chloride,  a  white,  stick}^  precipitate, 
called  2:)Iasmi7ie,  is  thrown  down,  after  the  removal  of  which,  by  filtration, 
the  plasma  will  not  spontaneously  coagulate.  This  jjJas^niiie  is  soluble 
in  dilute  neutral  saline  solutions,  and  the  solution  of  it  speedily  coagu- 
lates, producing  a  clot  composed  of  fibrin.  From  this  we  see  that  blood 
plasma  contains  a  substance  without  which  it  cannot  coagulate,  and  a 
solution  of  which,  is  spontaneously  coagulable.  This  substance  is  very 
soluble  in  dilute  saline  solutions,  and  is  not,  therefore,  fibrin,  which  is 
insoluble  in  these  fluids.  We  are,  therefore,  led  to  the  belief  that  plas- 
mine  produces  or  is  converted  into  fibrin,  when  clotting  of  fluids  contain- 
ing it  takes  place. 

Nature  of  Plasmine. — There  seems  distinct  evidence  that  plasmine 
is  a  compound  body  made  up  of  two  or  more  substances,  and  that  it  is 
not  mere  soluble  fibrin.  This  view  is  based  upon  the  following  observa- 
tions:— There  exists  in  all  the  serous  cavities  of  the  body  in  health,  e.g., 
the  pericardium,  the  peritoneum,  and  the  pleura,  a  certain  small  amount 
of  transparent  fluid,  generally  of  a  pale  straw  color,  which  in  diseased 
conditions  may  be  greatly  increased.  It  somewhat  resembles  serum  in 
appearance,  but  in  reality  differs  from  it,  and  is  probably  identical  with 
plasma.  This  serous  fluid  is  not,  as  a  rule,  spontaneously  coagulable,  but 
may  be  made  to  clot  on  the  addition  of  serum,  which  is  also  a  fluid  which 
has  no  tendency  of  itself  to  coagulate.  The  clot  produced  consists  of 
fibrin,  and  the  clotting  is  identical  with  the  clotting  of  plasma.  From 
the  serous  fluid  (that  from  the  inflamed  tunica  vaginalis  testis  or  hydrocele 
fluid  is  mostly  used)  we  may  obtain,  by  saturating  it  with  solid  mag- 
nesium sulphate  or  sodium  chloride,  a  Avhite  viscid  substance  as  a  precipi- 
tate which  is  called  fibrinogen,  which  may  be  separated  by  filtration,  and 
is  then  capable  of  being  dissolved  in  water,  as  a  certain  amount  of  the 
neutral  salt  is  entangled  with  the  precipitate  sufficient  to  produce  a  dilute 
saline  solution  in  which  it  is  soluble.  Tliis  body  belongs  to  the  glolmli)i 
class  of  proteid  substances.  Its  solution  has  no  tendency  to  clot  of  itself. 
Fibrinogen  may  also  be  obtained  as  a  viscid  precipitate  from  hydrocele 
fluid  by  diluting  it  with  water,  and  passing  a  brisk  stream  of  carbon 
dioxide  gas  through  the  solution.  Now  if  serum  be  added  to  a  solution 
of  fibrinogen,  the  mixture  clots. 

From  serum  may  be  obtained  another  globulin  very  similar  in  i)ro])er- 
tics  to  fi})rinogen,  if  it  be  subjected  to  treatment  similar  to  either  of  the 
two  methods  by  whicli  fibrinogen  is  obtained  from  hydrocele  iluid;  this 
substance  is  called  para  globulin,  and  it  may  be  separated  by  filtration  ai  d 
dissolved  in  a  dilute  saline  solution  in  a  manner  similar  to  fibrinogen. 


THE  BLOOD. 


G9 


If  the  solutions  of  fibrinogen  and  ptiraglobulin  be  mixed,  the  mixture 
cannot  be  distinguished  from  a  sohition  of  plasmine,  and  like  that  solu- 
tion (in  a  great  majority  of  cases)  firmly  clots;  whereas  a  mixture  of  the 
hydrocele  fluid  and  serum,  from  which  they  have  been  respectively  taken, 
no  longer  does  so.  In  addition  to  this  evidence  of  the  compound  nature 
of  plasmine,  it  may  be  further  shown  that,  if  sufficient  care  be  taken, 
both  fibrinogen  and  paraglobulin  may  be  obtained  from  plasma:  fibrin- 
ogen, as  a  flaky  precipitate,  by  adding  carefully  1 3  per  cent,  of  crystalline 
sodium  chloride;  and  after  the  removal  of  fibrinogen  from  the  plasma  by 
filtration,  paraglobulin-  may  be  afterward  precipitated,  on  the  further 
addition  of  the  same  salt  or  of  magnesium  sulphate  to  the  filtrate.  It  is 
evident,  therefore,  that  both  these  substances  must  be  thrown  down  to- 
gether when  plasma  is  saturated  with  sodium  chloride  or  magnesium  sul- 
phate, and  that  the  mixture  of  the  two  corresponds  with  plasmine. 

Presence  of  a  Fibrin  Ferment. — So  far  it  has  been  shown  that 
plasmine,  the  antecedent  of  fibrin  in  blood,  to  the  possession  of  which 
blood  owes  its  power  of  coagulating,  is  not  a  simple  body,  but  is  composed 
of  at  least  two  factors — viz.,  fibrinogen  and  paraglobulin;  there  is  reason 
for  believing  that  yet  another  body  is  associated  with  them  in  plasmine 
to  produce  coagulation;  this  is  what  is  known  under  the  name  of  fibrin 
ferment  (Schmidt).  It  was  at  one  time  thought  that  the  reason  why 
hydrocele  fluid  coagulated  when  serum  was  added  to  it  was  that  the  latter 
fluid  supplied  the  paraglobulin  which  the  former  lacked;  this,  however, 
is  not  the  case,  as  hydrocele  does  not  lack  this  body,  and  if  paraglobulin, 
obtained  from  serum  by  the  carbonic  acid  method,  be  added  to  it,  it  will 
not  coagulate,  neither  will  a  mixture  of  solutions  of  fibrinogen  and  para- 
globulin obtained  in  the  same  way.  But  if  paraglobulin,  obtained  by 
the  saturation  method,  be  added  to  hydrocele  fluid,  it  will  clot,  as  will 
also,  as  we  have  seen  above,  a  mixed  solution  of  fibrinogen  and  para- 
globulin, when  obtained  by  the  saturation  method.  From  this  it  is  evident 
that  in  plasmine  there  is  something  more  than  the  two  bodies  above  men- 
tioned, and  that  this  something  is  precipitated  with  the  paraglobulin  by 
the  saturation  method,  and  is  not  precipitated  by  the  carbonic  acid 
method.  The  following  experiments  show  that  it  is  of  the  nature  of  a 
ferment.  If  defibrinated  blood  or  serum  be  kept  in  a  stoppered  bottle 
with  its  own  bulk  of  alcohol  for  some  weeks,  all  the  proteid  matter  is  pre- 
cipitated in  a  coagulated  form;  if  the  precipitate  be  then  removed  by 
filtration,  dried  over  sulphuric  aci'd,  finely  powdered,  and  then  suspended 
in  water,  a  watery  extract  may  be  obtained  by  further  filtration,  contain- 
ing extremely  little,  if  any,  proteid  matter.  Yet  a  little  of  this  watery 
extract  will  determine  coagulation  in  fluids,  e.g.,  hydrocele  fluid  or 
diluted  plasma,  which  are  not  spontaneously  coagulable,  or  which  coagu- 
late slowly  and  with  difficulty.  It  will  also  cause  a  mixture  of  fibrinogen 
and  paraglobulin,  obtained  by  the  carbonic  acid  method,  to  clot.  This 


70 


HAND-BOOK  OF  PHYSIOLOGY. 


watery  extract  appears  to  contain  the  body  which  is  precipitated  with  the 
paragiobulin  by  the  saturation  method.  Its  active  properties  are  entirely 
destroyed  by  boiling.  The  amount  of  the  extract  added  does  not  influ- 
ence the  amount  of  the  clot  formed,  but  only  the  rapidity  of  clotting,  and 
moreover  the  active  substance  contained  in  the  extract  evidently  does  not 
form  part  of  the  clot,  as  it  may  be  obtained  from  the  serum  after  blood 
has  clotted.  So  that  the  third  factor,  which  is  contained  in  the  aqueous 
extract  of  blood,  belongs  to  that  class  of  bodies  which  promote  the  union 
of  other  bodies,  or  cause  changes  in  other  bodies,  without  themselves 
entering  into  union  or  undergoing  change,  i.e.  ferments.  The  third  sub- 
stance has,  therefore,  received  the  name  fibrin  ferment.  This  ferment 
is  developed  in  blood  soon  after  it  has  been  shed,  and  its  amount  appears 
to  increase  for  a  certain  time  afterward  (p.  74). 

The  part  played  by  Paragiobulin. — So  far  we  have  seen  that 
plasmine  is  a  body  composed  of  three  substances,  viz.,  fibrinogen,  para- 
giobulin, and  fibrin  ferment.  The  question  presents  itself,  are  these 
three  bodies  actively  concerned  in  the  formation  of  fibrin?  Here  we 
come  to  a  point  about  which  two  distinct  opinions  prevail,  and  wliich  it 
will  be  necessary  to  mention.  Schmidt  holds  that  fibrin  is  produced  by 
the  interaction  of  the  two  proteid  bodies,  viz.,  fibrinogen  and  para- 
giobulin, brought  about  by  the  presence  of  a  special  fibrin  ferment.  Also, 
that  when  coagulation  does  not  occur  in  serum,  which  contains  para- 
giobulin and  the  fibrin  ferment,  the  non-coagulation  is  accounted  for  by 
lack  of  fibrinogen,  and  when  it  does  not  occur  in  fluids  which  contain 
fibrinogen,  it  is  due  to  the  absence  of  paragiobulin,  or  of  the  ferment,  or 
of  both.  It  Avill  be  seen  that,  according  to  this  view,  paragiobulin  has 
a  very  important  fibrino-plastic  property.  The  other  opinion,  held  by 
Hammersten,  is  that  paragiobulin  is  not  an  essential  in  coagulation,  or 
at  any  rate  does  not  take  an  active  part  in  the  process.  He  believes  that 
paragiobulin  possesses  the  property  in  common  with  many  other  bodies 
of  combining  with — or  decomposing,  and  so  rendering  inert — certain 
substances  which  have  the  power  of  prev-enting  the  formation  or  precipi- 
tation of  fibrin,  this  power  of  preventing  coagulation  being  well  known 
to  belong  to  tlie  free  alkalies,  to  the  alkaline  carbonates,  and  to  certain 
salts;  and  he  looks  upon  fibrin  as  formed  from  -fibrinogen,  which  is  either 
(1)  decomposed  into  that  substance  with  the  production  of  some  other 
substances;  or  (2)  bodily  converted  into  it  uiuler  the  action  of  a  ferment, 
which  is  frequently  precipitated  with  paragiobulin. 

Influence  of  Salts  on  Coagulation. — It  is  believed  that  the  pres- 
ence of  a  certain  but  small  amount  of  salts,  especially  of  sodium  chloride, 
is  necessary  for  coagulation,  and  that  without  it,  clotting  cannot  take 
])la(;e. 

Sources  of  the  Fibrin  Generators. — It  has  been  previously  re- 
marked that  the  colorless  corpuscles  which  arc  always  present  in  snuiller 


THE  BLOOD. 


71 


or  greater  numbers  in  the  plasma,  even  when  this  has  been  freed  from 
colored  corpuscles,  have  an  important  share  in  the  production  of  the  clot. 
The  proofs  of  this  maybe  briefly  summarized  as  follows: — (1)  That  all 
strongly  coagulable  fluids  contain  colorless  corpuscles  almost  in  direct 
proportion  to  their  coagulability;  (2)  That  clots  formed  on  foreign  bodies, 
such  as  needles  inserted  into  the  interior  of  living  blood-vessels,  are  pre- 
ceded by  an  aggregation  of  colorless  corpuscles;  (3)  That  plasma  in 
which  the  colorless  corpuscles  happen  to  be  scanty,  clots  feebxy;  (4)  That 
if  horse's  blood  be  kept  in  the  cold,  so  that  the  corpuscles  subside,  it 
will  be  found  that  the  lowest  stratum,  containing  chiefly  colored  cor- 
puscles, will,  if  removed,  clot  feebly,  as  it  contains  little  of  the  fibrin 
factors;  whereas  the  colorless  plasma,  especially  the  lower  layers  of  it  in 
which  the  colorless  corpuscles  are  most  numerous,  will  clot  well,  but  if 
filtered  in  the  cold  will  not  clot  so  well,  indicating  ^hat  when  filtered 
nearly  free  from  colorless  corpuscles  even  the  plasma  does  not  contain  suffi- 
cient of  all  the  fibrin  factors  to  produce  thorough  coagulation;  (5)  In  a 
drop  of  coagulating  blood,  observed  under  the  miscroscope,  the  fibrin 
fibrils  are  seen  to  start  from  the  colorless  corpuscles. 

Although  the  intimate  connection  of  the  colorless  corpuscles  with  the 
process  of  coagulation  seems  indubitable,  for  the  reasons  just  given,  the 
exact  share  which  they  have  in  contributing  the  various  fibrin  factors 
remains  still  uncertain.  It  is  generally  believed  that  the  fibrin-ferment 
at  any  rate  is  contributed  by  them,  inasmuch  as  the  quantity  of  this  sub- 
stance obtainable  from  plasma  bears  a  direct  relation  to  the  numbers  of 
colorless  corpuscles  which  the  plasma  contains.  Many  believe  that  the 
fibrinogen  also  is  wholly  or  in  part  derived  from  them. 

Conditions  affecting  Coagulation. — The  coagulation  of  the  blood 
is  hastened  by  the  following  means: — 

1.  Moderate  warmth,— from  about  100°  to  120°  F.  (37-8—49°  C). 

2.  Rest  is  favorable  to  the  coagulation  of  blood.  Blood,  of  which  the 
whole  mass  is  kept  in  uniform  motion,  as  when  a  closed  vessel  completely 
filled  with  it  is  constantly  moved,  coagulates  very  slowly  and  imper- 
fectly. 

3.  Contact  with  foreign  matter,  and  especially  multiplication  of 
the  points  of  contact.  Thus,  coagulated  fibrin  may  be  quickly  obtained 
from  liquid  blood  by  stirring  it  with  a  bundle  of  small  twigs;  and  even 
in  the  living  body  the  blood  will  coagulate  upon  rough  bodies  projecting 
into  the  vessels;  as,  for  example,  upon  threads  passed  through  them,  or 
upon  the  heart's  valves  roughened  by  inflammatory  deposits  or  calcareous 
accumulations. 

1.  The  free  access  of  air. — Coagulation  is  quicker  in  shallow  than 
in  tall  and  narrow  vessels. 


72 


HAND-BOOK  OF  PHYSIOLOGY. 


5.  The  addition  of  less  than  twice  the  bulk  of  water. 

The  blood  last  drawn  is  said  to  coagulate  more  quickly  than  the  first. 
The  coagulation  of  the  blood  is  retarded,  suspended,  or  prevented 
by  the  following  means: — 

1.  Cold  retards  coagulation;  and  so  long  as  blood  is  kept  at  a  tem- 
perature, 32°  F.  (0°  C),  it  will  not  coagulate  at  all.  Freezing  the  blood, 
of  course,  prevents  its  coagulation;  yet  it  will  coagulate,  though  not  firmly, 
if  thawed  after  being  frozen;  and  it  will  do  so,  even  after  it  has  been  frozen 
for  several  months.  A  higher  temperature  than  120°  F.  (49°  C. )  retards  coag- 
ulation, or,  by  coagulating  the  albumen  of  the  serum,  prevents  it  altogether. 

2.  The  addition  of  water  in  greater  proportion  than  twice  the 
bulk  of  the  blood. 

3.  Contact  with  living  tissues,  and  especially  with  the  interior 
of  a  living  blood-vessel. 

4.  The  addition  of  neutral  salts  in  the  proportion  of  2  or  3  per 
cent,  and  upward.  When  added  in  large  proportion  most  of  these  saline 
substances  prevent  coagulation  altogether.  Coagulation,  however,  ensues 
on  dilution  with  water.  The  time  during  which  blood  can  be  thus  pre- 
served in  a  liquid  state  and  coagulated  by  the  addition  of  water,  is  quite 
indefinite. 

5.  Imperfect  Aeration, — as  in  the  blood  of  those  who  die  by  as- 
phyxia. 

6.  In  inflammatory  states  of  the  system  the  blood  coagulates 
more  slowly  although  more  firmly. 

7.  Coagulation  is  retarded  by  exclusion  of  the  blood  from  the 

air,  as  by  pouring  oil  on  the  surface,  etc.  In  vacuo,  the  blood  coagulates 
quickly;  but  Lister  thinks  that  the  rapidity  of  the  process  is  due  to  the 
bubbling  which  ensues  from  the  escape  of  gas,  and  to  the  blood  being 
thus  brought  more  freely  into  contact  with  the  containing  vessel. 

8.  The  coagulation  of  the  blood  is  prevented  altogether  by  the  ad- 
dition of  strong  acids  and  caustic  alkalies. 

9.  It  has  been  believed,  and  cliiefly  on  the  authority  of  Hunter,  that 
after  certain  modes  of  death  the  blood  does  not  coagulate: 
he  enumerates  the  death  by  lightning,  over-exertion  (as  in  animals  hunted 
to  death),  blows  on  the  stomach,  fits  of  anger.  He  says,  "I  have  seen 
instances  of  them  all."  Doubtless  he  had  done  so;  but  the  results  of  such 
events  are  not  constant.  The  blood  has  been  often  observed  coagulated 
in  the  bodies  of  animals  killed  by  lightning  or  an  electric  shock;  and 
Gulliver  has  published  instances  in  which  he  found  clots  in  the  hearts 
of  liiires  and  stags  Inuitod  to  death,  aiul  of  corks  killed  in  fighting. 

Cause  of  the  fluidity  of  the  blood  within  the  living  body. — 
Very  closely  connected  with  the  problem  of  the  coagulation  of  the  blood 
arises  the  question, — why  does  the  blood  remain  li(]uid  within  the  living 
body?    AVe  liave  certain  pathological  and  experimental  facts,  a])parently 


THE  BLOOD. 


73 


opposed  to  one  another,  which  bear  upon  it,  and  these  may  be,  for  the 
sake  of  clearness,  classed  under  two  heads: — 

(1)  Blood  ivill  coagulate  within  the  living  body  under  certain  condi- 
tions,— for  example,  on  ligaturing  an  artery,  whereby  the  inner  and  mid- 
dle coats  are  generally  ruptured,  a  clot  will  form  within  it,  or  by  passing 
a  needle  through  the  coats  of  the  vessel  into  the  blood  stream  a  clot  will 
gradually  form  upon  it.  Other  foreign  bodies,  e.g.  wire,  thready  etc., 
produce  the  same  effect.  It  is  a  well-known  fact  that  small  clots  are  apt 
to  form  upon  the  roughened  edges  of  the  valves  of  the  heart  when  the 
roughness  has  been  produced  by  inflammation,  as  in  endocarditis,  and  it 
is  also  equally  true  that  aneurisms  of  arteries  are  sometimes  spontaneously 
cured  by  the  deposition  within  them,  layer  by  layer,  of  fibrin  from  the 
blood  stream,  which  natural  cure  it  is  the  aim  of  the  physician  or  surgeon 
to  imitate. 

(2)  Blood  will  remain  liquid  under  certain  conditions  outside  the  body, 
without  the  addition  of  any  re-agent,  even  if  exposed  to  the  air  at  the 
ordinary  temperature.  It  is  well  known  that  blood  remains  fluid  in  the 
body  for  some  time  after  death,  and  it  is  only  after  rigor  mortis  has  oc- 
curred that  the  blood  is  found  clotted.  It  has  been  demonstrated  by 
Hewson,  and  also  by  Lister,  that  if  a  large  vein  in  the  horse  or  similar 
animal  be  ligatured  in  two  places  some  inches  apart,  and  after  some  time 
be  opened,  the  blood  contained  within  it  will  be  found  fluid,  and  that 
coagulation  will  occur  only  after  a  considerable  time.  But  this  is  not 
due  to  occlusion  from  the  air  simply.  Lister  further  showed  that  if  the 
vein  with  the  blood  contained  within  it  be  removed  from  the  body  and 
then  be  carefully  opened,  the  blood  might  be  poured  from  the  vein  into 
another  similarly  prepared,  as  from  one  test-tube  into  another,  thereby 
suffering  free  exposure  to  the  air,  without  coagulation  occurring  as  long 
as  the  vessels  retain  their  vitality.  If  the  endothelial  lining  of  the  vein, 
however,  be  injured,  the  blood  will  not  remain  liquid.  Again,  blood  will 
remain  liquid  for  days  in  the  heart  of  a  turtle,  which  continues  to  beat 
for  a  very  long  time  after  removal  from  the  body. 

Any  theory  which  aims  at  explaining  the  fluidity  under  the  usual 
conditions  of  the  blood  within  the  living  body  must  reconcile  the  above 
apparently  contradictory  facts,  and  must  at  the  same  time  be  made  to  in- 
clude all  the  other  known  facts  concerning  the  coagulation  of  the  blood. 
We  may  therefore  dismiss  as  insufficient  the  following; — ^that  coagulation 
is  due  to  exposure  to  the  air  or  oxygen;  that  it  is  due  to  the  cessation  of 
the  circulatory  movement;  that  it  is  due  to  evolution  of  various  gases,  or 
to  the  loss  of  heat. 

Two  theories,  those  of  Lister  and  Briicke,  remain.  The  former  sup- 
poses that  the  blood  has  no  natural  tendency  to  clot,  but  that  its  coagula- 
tion out  of  the  body  is  due  to  the  action  of  foreign  matter  with  which  it 
happens  to  be  brought  into  contact,  and  in  the  body  to  conditions  of  the 


74 


HAND-BOOK  OF  PHYSIOLOGY. 


tissues  whicli  cause  them  to  act  toward  it  like  foreign  matter.  The  lat- 
ter, on  the  other  hand,  supposes  that  there  is  a  natural  tendency  on  the 
part  of  the  blood  to  clot,  but  that  this  is  restrained  in  the  living  body 
by  some  inhibitory  power  resident  in  the  walls  of  the  containing  vessels. 

Support  was  once  thought  to  be  given  to  Briicke's  and  like  theories 
by  cases  of  injury,  in  which  blood  extravasated  in  the  living  body  has 
seemed  to  remain  uncoagulated  for  weeks,  or  even  months,  on  account  of 
its  contact  with  living  tissues.  But  the  supposed  facts  have  been  shown  to 
be  without  foundation.  The  blood-like  fluid  in  such  cases  is  not  uncoag- 
ulated blood,  but  a  mixture  of  serum  and  blood-corpuscles,  with  a  certain 
proportion  of  clot  in  various  stages  of  disintegration.    (Morrant  Baker.) 

As  the  blood  must  contain  the  substances  from  which  fibrin  is  formed, 
and  as  the  re-arrangement  of  these  substances  occurs  very  quickly  when- 
ever the  blood  is  shed,  so  that  it  is  somewhat  difficult  to  prevent  coagula- 
tion, it  seems  more  reasonable  to  hold  with  Briicke,  that  the  blood  has  a 
strong  tendency  to  clot,  rather  than  with  Lister,  that  it  has  no  special 
tendency  thereto. 

It  has  been  recently  suggested  that  the  reason  why  blood  does  not 
coagulate  in  the  living  vessels,  is  that  the  factors  which  we  have  seen  are 
necessary  for  the  formation  of  fibrin  are  not  in  the  exact  state  required 
for  its  production,  and  that  the  fibrin  ferment  is  not  formed  or  is  not,  at 
any  rate,  free  in  the  living  blood,  but  that  it  is  produced  (or  set  free)  at 
the  moment  of  coagulation  by  the  disintegration  of  the  colorless  corpuscles. 
This  supposition  is  certainly  plausible,  but  if  it  be  a  true  one,  it  must  be 
assumed  either  that  the  living  blood-vessels  exert  a  restraining  influence 
upon  the  disintegration  of  the  corpuscles  in  sufficient  numbers  to  form  a 
clot,  or  that  they  render  inert  any  small  amount  of  fibrin  ferment  which 
may  have  been  set  free  by  the  disintegration  of  a  few  corpuscles;  as  it  is 
certain  that  corpuscles  of  all  kinds  must  from  time  to  time  disintegrate 
in  the  blood  without  causing  it  to  clot;  and,  secondly,  that  shed  and 
defibrinated  blood  which  contains  blood  corpuscles,  broken  down  and  dis- 
integrated, will  not,  when  injected  into  the  vessels  of  an  animal,  produce 
clotting.  There  must  be  a  distinct  difference,  therefore,  if  only  in 
amount,  between  the  normal  disintegration  of  a  few  colorless  corpuscles  in 
the  living  uninjured  blood-vessels  and  the  abnormal  disintegration  of  a 
large  number  which  occurs  whenever  tlie  blood  is  shed  without  suitable 
precaution,  or  when  coaguhition  is  unrestrained  by  the  neighborhood  of 
the  living  uninjured  blood-vessels. 

The  I^looi)  Corpuscles  or  Blood-Cells. 

There  are  two  priiicipMl  forms  of  corpuscles,  ihc  red  and  the  white, 
or,  as  they  are  now  frc(|ii(Mitly  named,  the  colored  and  the  colorless. 
In  the  moist  state,  tlio  red  corpuscles  form  abont  -15  per  cent,  by  weight. 


THE  BLOOD 


75 


of  the  whole  mass  of  the  blood.  The  proportion  of  colorless  corpuscles 
is  only  as  1  to  500  or  600  of  the  colored. 

Red  or  Colored  Corpuscles. — Human  red  blood-corpuscles  are 
circular,  biconcave  disks  with  rounded  edges,  from  to  ^^Vo  i^'^h 
diameter,  and  t^-^q-  i^^^  thickness,  becoming  flat  or  convex  on  addi- 
tion of  water.  When  viewed  singly,  they  appear  of  a  pale  yellowish  tinge; 
the  deep  red  color  which  they  give  to  the  blood  being  observable  in  them 
only  when  they  are  seen  en  masse.  They  are  composed  of  a  colorless, 
structureless,  and  transparent  filmy  framework  or  stroma,  infiltrated  in 
all  parts  by  a  red  coloring  matter  termed  Immoglolin.  The  stroma  is 
tough  and  elastic,  so  that,  as  the  cells  circulate,  they  admit  of  elonga,tion 
and  other  changes  of  form,  in  adaptation  to  the  vessels,  yet  recover  their 
natural  shape  as  soon  as  they  escape  from  compression.  The  term  cell, 
in  the  sense  of  a  bag  or  sac,  is  inapplicable  to  the  red  blood  corpus- 
cle; and  it  must  be  considered,  if  not 
stolid  throughout,  yet  as  having  no  such 
variety  of  consistence  in  different  parts 
-as  to  justify  the  notion  ol  its  being  a 
membranous  sac  with  fiuid  contents. 
The  stroma  exists  in  all  parts  of  its  sub- 
stance, and  the  coloring-matter  uni- 
formly pervades  this,  and  is  not  merely 
surrounded  by  and  mechanically  en- 
closed within  the  outer  wall  of  the 
corpuscle.  The  red  corpuscles  have 
no  nuclei,  although,  in  their  usual  state, 
the  unequal  refraction  of  transmitted  fig.  68.-Red  corpuscles  in  rouleaux.  At 
light  gives  the  appearance  of  a  central   c.,  a,  are  two  white  corpuscles. 

spot,  brighter  or  darker  than  the  border,  according  as  it  is  viewed  in  or 
out  of  focus.    Their  specific  gravity  is  about  1088. 

Varieties. — The  red  corpuscles  are  not  all  alike,  some  being  rather 
larger,  paler,  and  less  regular  than  the  majority,  and  sometimes  flat  or 
slightly  convex,  with  a  shining  particle  apparent  like  a  nucleolus.  In 
almost  every  specimen  of  blood  may  be  also  observed  a  certain  number  of 
corpuscles  smaller  than  the  rest.  They  are  termed  microcytes,  and  are 
probably  immature  corpuscles. 

A  peculiar  property  of  the  red  corpuscles,  exaggerated  in  inflammatory 
blood,  may  be  here  again  noticed,  i.e.,  their  great  tendency  to  adhere  to- 
gether in  rolls  or  columns,  like  piles  of  coins.  These  rolls  quickly  fasten 
together  by  their  ends,  and  cluster;  so  that,  when  the  blood  is  spread  out 
thinly  on  a  glass,  they  form  a  kind  of  irregular  network,  with  crowds  of 
corpuscles  at  the  several  points  corresponding  with  the  knots  of  the  net 
(Fig.  68).  Hence,  the  clot  formed  in  such  a  thin  layer  of  blood  looks 
mottled  with  blotches  of  pink  upon  a  white  ground,  and  in  a  larger  quan- 


76 


HAND-BOOK  OF  PHYSIOLOGY. 


tity  of  such  blood  help,  by  the  consequent  rapid  subsidence  of  the  cor- 
puscles, in  the  formation  of  the  bulfy  coat  already  referred  to. 

This  tendency  on  the  part  of  the  red  corpuscles,  to  form  rouleaux,  is 
probably  only  a  physical  phenomenon,  comparable  to  the  collection  into 
somewhat  similar  rouleaux  of  discs  of  corks  when  they  are  partially  im- 
mersed in  water.  (Xorris.) 


3Iammals.     Birds.      Reptiles.  Amphibia.  Fish. 


Fig.  69.1 


'  The  above  illustration  is  somewhat  altered  from  a  drawinc;  by  Gulliver,  in  the 
Proceed.  Zool.  Society,  and  exhibits  the  typical  characters  of  the  red  blood-cells  in  the 
main  divisions  of  the  Vcrtebrata.  The  fractions  are  those  of  an  inch,  and  represent 
the  averai!;('  diameter.  In  the  case  of  the  oval  cells,  only  the  lonii;  diameter  is  here 
f^iven.  It  is  remarkable,  that  althoui^h  the  size  of  the  red  blood-cells  varies  so  much 
in  the  different  classes  of  the  vertebrate  kini^dom,  that  of  the  ^vhite  corpuscles  re- 
mains comparatively  uniform,  and  thus  they  are,  in  some  animals,  nuich  greater,  in 
others  much  l(;ss  than  the  red  corpuscles  existing  side  by  side  with  them. 


THE  BLOOD. 


77 


Action  of  Reagents. — Considerable  light  has  been  thrown  on  the 
physical  and  clioniical  constitution  of  red  blood -cells  by  studying  the 
eifects  produced  by  mechanical  means  and  by  various  reagents:  the  fol- 
lowing is  a  brief  stimmary  of  these  reactions: — 

Pressure. — If  the  red  blood-cells  of  a  frog  or  man  are  gently  squeezed, 
they  exhibit  a  wrinkling  of  the  surface,  which  clearly  indicates  that  there 
is  a  superficial  pellicle  partly  differentiated  from  the  softer  mass  within; 
again,  if  a  needle  be  rapidly  drawn  across  a  drop  of  blood,  several  cor- 
puscles will  be  found  cut  in  two,  but  this  is  not  accompanied  by  any  es- 
cape of  cell  contents;  the  two  halves,  on  the  contrary,  assume  a  rounded 
form,  proving  clearly  that  the  corpuscles  are  not  mere  membranous  sacs 
with  fluid  contents  like  fat-cells. 

Fluids. —  Water. — When  water  is  added  gradually  to  frog's  blood,  the 
oval  disc-shaped  corpuscles  become  spherical,  and  gradually  discharge 
their  haemoglobin,  a  pale,  transparent  stroma  being  left  behind;  human 
red  blood-cells  change  from  a  discoidal  to  a  spheroidal  form,  and  dis- 
charge their  cell-contents,  becoming  quite  transparent  and  all  but  invisible. 

8aline  solution  (dilute)  produces  no  appreciable  effect  on  the  red 


blood-cells  of  the  frog.  In  the  red  blood-cells  of  man  the  discoid  shape  is 
exchanged  for  a  spherical  one,  with  spinous  projections,  like  a  horse- 
chestnut  (Fig.  70).  Their  original  forms  can  be  at  once  restored  by  the 
use  of  carbonic  acid. 

Acetic  acid  (dilute)  causes  the  nucleus  of  the  red  blood  cells  in  the 
frog  to  become  more  clearly  defined;  if  the  action  is  prolonged,  the  nu- 
cleus becomes  strongly  granulated,  and.  all  the  coloring  matter  seems  to 
be  concentrated  in  it,  the  surrounding  cell-substance  and  outline  of  the 
cell  becoming  almost  invisible;  after  a  time  the  cells  lose  their  color  alto- 
gether. The  cells  in  the  figure  (Fig.  71)  represent  the  successive  stages  of 
the  change.  A  similar  loss  of  color  occurs  in  the  red  cells  of  human  blood, 
which,  however,  from  the  absence  of  nuclei,  seem  to  disappear  entirely. 

Alhalies  cause  the  red  blood-cells  to  swell  and  finally  disappear. 

Chloroform  added  to  the  red  blood-cells  of  the  frog  causes  them  to 
part  with  their  haemoglobin;  the  stroma  of  the  cells  becomes  gradually 
broken  up.    A  similar  effect  is  produced  on  the  human  red  blood-cell. 

Tannin. — When  a  2  per  cent,  solution  of  tannic  acid  is  applied  to 
frog's  blood  it  causes  the  appearance  of  a  sharply-defined  little  knob,  pro- 
jecting from  the  free  surface:  the  coloring  matter  becomes  at  the  same 
time  concentrated  in  the  nucleus,  which  grows  more  distinct  (Fig.  72). 


Fig.  70. 


Fig.  71. 


Fig.  72. 


78 


HAND-BOOK  OF  PHYSIOLOGY. 


A  somewhat  similar  effect  is  produced  on  the  human  red  blood-cell. 
(Eoberts.)  Magenta,  when  applied  to  the  red  blood-cells  of  the  [frog, 
produces  a  similar  little  knob  or  knobs,  at  the  same  time  staining  the 
nucleus  and  causing  the  discharge  of  the  hsemoglobin.  (Eoberts.)  The 
first  effect  of  the  magenta  is  to  cause  the  discharge  of  the  haemoglobin, 
then  the  nucleus  becomes  suddenly  stained,  and  lastly  a  finely  granular 
matter  issues  through  the  wall  of  the  corpuscle,  becoming  stained  by  the 
magenta,  and  a  macula  is  formed  at  the  point  of  escape.  A  similar 
macula  is  produced  in  the  human  red  blood-cell. 

Boracic  acid. — A  2  per  cent,  solution  applied  to  nucleated  red  blood- 
cells  (frog)  will  cause  the  concentration  of  all  the  coloring  matter  in  the 
nucleus;  the  colored  body  thus  formed  gradually  quits  its  central  position, 
and  comes  to  be  partly,  sometimes  entirely,  protruded  from  the  surface 
of  the  now  colorless  cell  (Fig.  73).  The  result  of  this  experiment  led 
Brlicke  to  distinguish  the  colored  contents  of  the  cell  (zooid)  from  its 
colorless  stroma  (oecoid).  When  applied  to  the  non-nucleated  mammalian 
corpuscle  its  effect  merely  resembles  that  of  other  dilute  acids. 

Gases — Carlonic  acid. — If  the  red  blood-cells  of  a  frog  be  first  exposed 


Fig.  73.  Fig.  74.  Fig.  75.  Fig.  76. 


to  the  action  of  water-vapor  (which  renders  their  outer  pellicle  more 
readily  permeable  to  gases),  and  then  acted  on  by  carbonic  acid,  the 
nuclei  immediately  become  clearly  defined  and  strongly  granulated;  when 
air  or  oxygen  is  admitted  the  original  appearance  is  at  once  restored. 
The  upper  and  lower  cell  in  Fig.  74  show  the  effect  of  carbonic  acid;  the 
middle  one  the  effect  of  the  re-admission  of  air.  These  effects  can  be 
reproduced  five  or  six  times  in  succession.  If,  however,  the  action  of  the 
carbonic  acid  be  much  prolonged,  the  granulation  of  the  nucleus  becomes 
permanent;  it  appears  to  depend  on  a  coagulation  of  the  paraglobulin. 
(Strieker.) 

Ammonia. — Its  effects  seem  to  vary  according  to  the  degree  of  con- 
centration. Sometimes  the  outline  of  the  corpuscles  becomes  distinctly 
crenatcd;  at  other  times  the  effect  resembles  that  of  boracic  acid,  while 
in  other  cases  the  edges  of  the  corpuscles  begin  to  break  up.  (Lankester.) 

The  effect  of  heat  up  to  120°— 140°  F.  (50°— 60°  0.)  is  to 
cause  the  formation  of  a  number  of  bud-like  ])rocesses  (Fig.  75). 

ElpciricUy  causes  the  red  blood-corpusclos  to  become  crenatcd,  and 
at  lengtli  mulberry-like.  Finally  they  recover  their  round  form  and 
become  quite  i)ale. 


THE  BLOOD. 


79 


The  general  conclusions  to  be  drawn  from  these  observations  have 
been  summed  up  as  follows  by  Prof.  Ray  Lankester: — 

"The  red  blood-corpuscle  of  the  vertebrata  is  a  viscid,  and  at  the  same 
time  elastic  disc,  oval  or  round  in  outline,  its  surface  being  differentiated 
somewhat  from  the  underlying  material,  and  forming  a  pellicle  or  mem- 
brane of  great  tenuity,  not  distinguishable  with  the  highest  powers 
(whilst  the  corpuscle  is  normal  and  living),  and  having  no  pronounced  inner 
limitation.  The  viscid  mass  consists  of  (or  rather  yields,  since  the  state 
of  combination  of  the  components  is  not  known)  a  variety  of  albuminoid 
and  other  bodies,  the  most  easily  separable  of  which  is  haemoglobin;  sec- 
ondly, the  matter  which  segregates  to  form  Eoberts's  macula;  and  thirdly, 
a  residuary  stroma,  apparently  homogeneous  in  the  mammalia  (excepting 
as  far  as  the  outer  surface  or  pellicle  may  be  of  a  different  chemical 
nature),  but  containing  in  the  other  vertebrata  a  sharply  definable 
nucleus,  this  nucleus  being  already  differentiated,  but  not  sharply  deline- 
ated during  life,  and  consisting  of,  or  separable  into,  at  least  two  com- 
ponents, one  (paraglobulin)  precipitable  by  carbon  dioxide,  and  remov- 
able by  the  action  of  weak  ammonia;  the  other  pellucid,  and  not  gran- 
ulated by  acids."' 

The  White  or  Colorless  Corpuscles. — In  human  olood  the  white 
or  colorless  corpuscles  or  leucocytes  are  nearly  spherical  masses  of 
granular  protoplasm  without  cell  wall.  The  granular  appearance,  more 
marked  in  some  than  in  others  {vide  infra),  is  due  to  the  presence  of  par- 
ticles probably  of  a  fatty  nature.  In  all  cases  one  or  more  nuclei  exist  in 
each  corpuscle.  The  size  of  the  corpuscle  averages  g-^^-g-  of  an  inch  in 
diameter. 

In  health,  the  proportion  of  white  to  red  corpuscles,  which,  taking 
an  average,  is  about  1  to  500  or  600,  varies  considerably  even  in  the 
course  of  the  same  day.  The  variations  appear  to  depend  chiefly  on  the 
amount  and  probably  also  on  the  kind  a  b 

of  food  taken;  the  number  of  leuco- 
cytes being  very  considerably  increased 
by  a  meal,  and  diminished  again  on 
fasting.  Also  in  young  persons,  dur- 
ing pregnancy,  and  after  great  loss  fig.  77.-A.  Three  colored  biood-corpi^dls. 
of  blood,  there  is  a  larger  proportion  ?y  Sfc^a^SS^lM^^ 
of  colorless  blood-corpuscles,  which  x 

probably  shows  that  they  are  more  rapidly  formed  under  these  circum- 
stances.   In  old  age,  on  the  other  hand,  their  proportion  is  diminished. 

Varieties. — The  colorless  corpuscles  present  greater  diversities  of 
form  than  the  red  ones  do.  Two  chief  varieties  are  to  be  seen  in  human 
blood;  one  which  contains  a  considerable  number  of  granules,  and  the 
other  which  is  paler  and  less  granular.  In  size  the  variations  are  great, 
for  in  most  specimens  of  blood  it  is  possible  to  make  out,  in  addition  to 


80 


HAOT)-BOOK  OF  PHYSIOLOGY. 


the  full-sized  yarieties,  a  number  of  smaller  corpuscles,  consisting  of  a 
large  spherical  nucleus  surrounded  by  a  variable  amount  of  more  or  less 
granular  protoplasm.  The  small  corpuscles  are,  in  all  probability,  the 
undeveloped  forms  of  the  others,  and  are  derived  from  the  cells  of  the 
lymph.  Besides  the  above-mentioned  varieties,  Schmidt  describes  another 
form  which  he  looks  upon  as  intermediate  between  the  colored  and  the 
colorless  forms,  viz.,  certain  corpuscles  which  contain  red  granules  of 
hemoglobin  in  their  protoplasm.  The  different  varieties  of  colorless  cor- 
puscles are  especially  well  seen  in  the  blood  of  frogs,  newts,  and  other 
cold-blooded  animals. 

AmcEboid  movement. — A  remarkable  property  of  the  colorless  cor- 
puscles consists  in  their  capability  of  spontaneously  changing  their  shape. 
This  was  first  demonstrated  by  Wharton  Jones  in  the  blood  of  the  skate. 
If  a  drop  of  blood  be  examined  with  a  high  power  of  the  microscope  on 
a  warm  stage,  or,  in  other  words,  under  conditions  by  which  loss  of  mois- 
ture is  prevented,  and  at  the  same  time  the  temperature  is  maintained  at 
about  that  of  the  blood  in  its  natural  state  within  the  walls  of  the  living 
vessels,  100°  F.  (37 '8°  C),  the  colorless  corpuscles  will  be  observed  slowly 
altering  their  shapes,  and  sending  out  processes  at  various  parts  of  their 
circumference.    This  alteration  of  shape,  which  can  be  most  conveniently 


YiG.  78. — Human  colorless  blood-corpuscle,  showing  its  successive  changes  of  outline  within 
ten  minutes  when  kept  moist  on  a  warm  stage.  (Schofield.) 


studied  in  the  newt's  blood,  is  called  amoeboid,  inasmuch  as  it  strongly 
resembles  the  movement  of  the  lowly  organized  amceha.  The  processes 
which  are  sent  out  are  either  lengthened  or  withdrawn.  If  lengthened, 
the  protoplasm  of  the  whole  corpuscle  flows  as  it  were  into  its  process, 
and  the  corpuscle  changes  its  position;  if  withdrawn,  protrusion  of 
another  process  at  a  different  point  of  the  circumference  speedily  follows. 
The  change  of  position  of  the  corpuscle  can  also  take  place  by  a  flowing 
movement  of  the  whole  mass,  and  in  this  case  the  locomotion  is  compar- 
atively rapid.  The  activity  both  in  the  processes  of  change  of  shape  and 
also  of  change  in  position,  is  much  more  marked  in  some  corpuscles,  viz., 
in  the  granular  variety,  than  in  others.  Klein  states  that  in  the  newt's 
blood  the  changes  are  especially  likely  to  occur  in  a  variety  of  the  colorless 
corpuscle,  which  consists  of  masses  of  finely  granular  protoplasm  with 
Jagged  outline,  containing  three  or  four  nuclei,  or  of  large  irregular 
masses  of  i)rotoplasm  containing  from  five  to  twenty  nuclei.  Another 
plienomenon  may  be  observed  in  such  a  specimen  of  blood,  viz.,  the  divi- 
sion of  the  c()rpus(iles,  which  occurs  in  the  following  way.  A  cleft  takes 
place  in  the  protoplasm  at  one  point,  which  becomes  deeper  and  deeper, 


•fllE  BLOOD. 


81 


and  then  by  the  lengthening  out  and  attenuation  of  the  connection,  and 
finally  by  its  rupture,  two  corpuscles  result.  The  nuclei  have  previously 
undergone  division.  The  cells  so  formed  are  said  to  be  remarkably  active 
in  their  movements.  Thus  we  see  that  the  rounded  form  which  the 
colorless  corpuscles  present  in  ordinary  microscopic  specimens  must  be 
looked  upon  as  the  shape  natural  to  a  dead  corpuscle  or  to  one  whose 
vitality  is  dormant  rather  than  as  the  shape  proper  to  one  living  and 
active. 

Action  of  re-agents  upon  the  colorless  corpuscles. — Feeding  the 
corpuscles. —  If  some  fine  pigment  granules,  e.g.,  powdered  vermilion, 
be  added  to  a  fluid  containing  colorless  blood-corpuscles,  on  a  glass  slide, 
these  will  be  observed,  under  the  microscope,  to  take  up  the  pigment.  In 
some  cases  colorless  corpuscles  have  been  seen  with  fragments  of  colored 
ones  thus  embedded  in  their  substance.  This  property  of  the  colorless 
corpuscles  is  especially  interesting  as  helping  still  further  to  connect  them 
with  the  lowest  forms  of  animal  life,  and  to  connect  both  with  the  organ- 
ized cells  of  which  the  higher  animals  are  composed. 

The  property  which  the  colorless  corpuscles  possess  of  passing  through 
the  walls  of  the  blood-vessels  will  be  described  later  on. 

Enumeration  of  the  Red  and  White  Corpuscles. — Several 
methods  are  employed  for  counting  the  blood-corpuscles,  most  of  them 
depending  upon  the  same  principle,  i.e.,  the  dilution  of  a  minute  volume 
of  blood  with  a  given  volume  of  a  colorless  solution  similar  in  specific 
gravity  to  blood  serum,  so  that  the  size  and  shape  of  the  corpuscles  is 
altered  as  little  as  possible.  A  minute  quantity  of  the  well-mixed  solu- 
tion is  then  taken,  examined  under  the  microscope,  either  in  a  flattened 
capillary  tube  (Malassez)  or  in  a  cell  (Hayem  &  Nachet,  Growers)  of 
known  capacity,  and  the  number .  of  corpuscles  in  a  measured  length  of 
the  tube,  or  in  a  given  area  of  the  cell  is  counted.  The  length  of  the 
tube  and  the  area  of  the  cell  are  ascertained  by  means  of  a  micrometer 
scale  in  the  microscope  ocular;  or  in  the  case  of  Gowers^  modification,  by 
the  division  of  the  cell  area  into  squares  of  known  size.  Having  ascer- 
tained the  number  of  corpuscles  in  the  diluted  blood,  it  is  easy  to  find 
out  the  number  in  a  given  volume  of  normal  blood.  Gowers^  modifica- 
tion of  Hayem  &  !N"achet's  instrument,  called  by  him  Hcemacytometer," 
appears  to  be  the  most  convenient  form  of  instrument  for  counting  the 
corpuscles,  and  as  such  will  alone  be  described  (Fig.  79).  It  consists  of 
a  small  pipette  (a),  which,  when  filled  up  to  a  mark  on  its  stem,  holds- 
995  cubic  millimetres.  It  is  furnished  with  an  india-rubber  tube  and 
glass  mouth-piece  to  facilitate  filling  and  emptying;  a  capillary  tube  (b) 
marked  to  hold  5  cubic  millimetres,  and  also  furnished  with  an  india- 
rubber  tube  and  mouthpiece;  a  small  glass  jar  (d)  in  which  the  dilution 
of  the  blood  is  performed;  a  glass  stirrer  (e)  for  mixing  the  blood 
thoroughly,  (r)  a  needle,  the  length  of  which  can  be  regulated  by  a 
Vol.  I.— 6. 


82 


HAND-BOOK  OF  PHYSIOLOGY. 


screw;  a  brass  stage  plate  (c)  carrying  a  glass  slide,  on  which  is  a  cell 
one-fifth  of  a  millimetre  deep,  and  the  bottom  of  which  is  divided  into 
one-tenth  millimetre  squares.  On  the  top  of  the  cell  rests  the  cover 
glass,  which  is  kept  in  its  place  by  the  pressure  of  two  springs  proceeding 
from  the  stage  plate.  A  standard  saline  solution  of  sodium  sulphate,  or 
similar  salt,  of  specific  gravity  1025,  is  made,  and  995  cubic  millimetres 
are  measured  by  means  of  the  pipette  into  the  glass  jar,  and  with  this  five 
cubic  millimetres  of  blood,  obtained  by  pricking  the  finger  with  a  needle, 
and  measured  in  the  capillary  pipette  (b),  are  thoroughly  mixed  by  the 


Fig.  79.— Hsemacytometer. 


glass  stirring-rod.  A  drop  of  this  diluted  blood  is  then  placed  in  the  cell 
and  covered  with  a  cover-glass,  which  is  fixed  in  position  by  means  of  the 
two  lateral  springs.  The  preparation  is  then  examined  under  a  micro- 
scope with  a  power  of  about  400  diameters,  and  focussed  until  the  line-s 
dividing  the  cell  into  squares  are  visible. 

After  a  short  delay,  the  red  corpuscles  which  have  sunk  to  the  bottom 
of  the  cell,  and  are  resting  on  the  squares,  are  counted  in  ten  squares, 
and  the  number  of  white  corpuscles  noted.  By  adding  together  the 
numbers  counted  in  ton  (one-tenth  millimetre)  squares  the  number  of 
corpuscles  in  one-cubic  millimetre  of  blood  is  obtained.  The  average 
number  of  corpuscles  per  viwh  cubic  millinu^tro  of  healthy  blood,  aecM^rd- 
ing  to  Vicrordt  and  Wolcker,  is  5,000,000  in  adult  men,  and  rather  fewer 
in  women. 


THE  BLOOD. 


83 


Chemical  Composition  of  the  Blood  in  Bulk. — 

Water  

Solids- 
Corpuscles 
Proteids  {ot  serum) 
Fibrin  (of  clot)  . 
Fatty  matters  (of  serum) 
Inorganic  salts  (of  serum) 
Gases,  kreatin,  urea  and  other  extractive  ) 
matter,  glucose  and  accidental  sub-  >• 
stances  ) 


784 


130 
70 
2-2 
1-4 

6 

6-4— 


216 


1,000 


Chemical  Composition  of  the  Red  Corpuscles.— Analysis  of  a 
thousand  parts  of  moist  blood  corpuscles  shows  the  following  as  the 
result: — 


Water 


.  688 
303.88 
8.12—312 


1,000 


Of  the  solids  the  most  important  is  HmmogloUn,  the  substance  to 
which  the  blood  owes  its  color.  It  constitutes,  as  will  be  seen  from  the 
appended  Table,  more  than  90  per  cent,  of  the  organic  matter  of  the 
corpuscles.  Besides  haemoglobin  there  are  proteid  ^  and  fatty  matters,  the 
former  chiefly  consisting  of  globulins,  and  the  latter  of  cholesterin  and 
lecithin. 

In  1000  parts  organic  matter  are  found: — 

,        Haemoglobin   905*4 

Proteids  86*7 

Fats  7-9 


1,000- 

Of  the  inorganic  salts  of  the  corpuscles,  with  the  iron  omitted- 


In  1000  parts  corpuscles  (Schmidt)  are  found 
Potassium  Chloride 
Phosphate 

sulphate 
Sodium  ^' 
Calcium  " 
Magnesium 
Soda 


•679 
•343 
•132 
•633 
•094 
•060 
•341 


7^282 


^  An  account  of  the  proteid  bodies,  etc.,  will  be  found  in  the  Appendix,  and  should 
be  referred  to  for  explanation  of  the  terms  employed  in  the  text. 


84 


HAND-BOOK  OF  PHYSIOLOGY. 


The  properties  of  hsemoglobin  will  be  considered  in  relation  to  the 
Gases  of  the  blood. 

Chemical  Composition  of  the  Colorless  Corpuscles.— In  conse- 
quence of  the  difficulty  of  obtaining  colorless  corpuscles  in  sufficient  num- 
ber to  make  an  analysis,  little  is  accurately  known  of  their  chemical  com- 
position; in  all  probability,  however,  the  stroma  of  the  corpuscles  is  made 
up  of  proteid  matter,  and  the  nucleus  of  nuclein,  a  nitrogenous  phos- 
phorus-containing body  akin  to  mucin,  capable  of  resisting  the  action  of 
the  gastric  juice.  The  proteid  matter  (globulin)  is  soluble  in  a  ten  per 
cent,  solution  of  sodium  chloride,  and  the  solution  is  precipitated  on  the 
addition  of  water,  by  heat  and  by  the  mineral  acids.  The  stroma  con- 
tains fatty  granules,  and  in  it  also  the  presence  of  glycogen  has  been 
demonstrated.  The  salts  of  the  corpuscles  are  chiefly  potassium,  and 
of  these  the  phosphate  is  in  greatest  amount. 

Chemical  Composition  of  the  Plasma  or  Liquor  Sanguinis. — 
The  liquid  part  of  the  blood,  the  plasma  or  liquor  sanguinis  in  which  the 
corpuscles  float,  may  be  obtained  in  the  ways  mentioned  under  the  head 
of  the  Coagulation  of  the  Blood.  In  it  are  the  fibrin  factors,  inasmuch 
as  when  exposed  to  the  ordinary  temperature  of  the  air  it  undergoes  coag- 
ulation and  splits  up  into  fibrin  and  serum.  It  differs  from  the  serum 
in  containing  fibrinogen,  but  in  appearance  and  in  reaction  it  closely 
resembles  that  fluid;  its  alkalinity,  however,  is  less  than  that  of  the 
serum  obtained  from  it.  It  may  be  freed  from  white  corpuscles  by  filtra- 
tion at  a  temperature  below  41  °F.  (5°C.) 

Fibrin. — The  part  played  by  fibrin  in  the  formation  of  a  clot  has 
been  already  described  (p.  66),  and  it  is  only  necessary  to  consider  here 
its  general  properties.  It  is  a  stringy  elastic  substance  belonging  to  the 
proteid  class  of  bodies.  It  is  insoluble  in  water  and  in  weak  saline  solu- 
tions, it  swells  up  into  a  transparent  jelly  when  placed  in  dilute-hydro- 
chloric acid,  but  does  not  dissolve,  but  in  strong  acid  it  dissolves,  pro- 
ducing acid-albumin;'  it  is  also  soluble  on  boiling  in  strong  saline  solu- 
tions. Blood  contains  only  '2  per  cent,  of  fibrin.  It  can  be  converted 
by  the  gastric  or  pancreatic  juice  into  peptone.  It  possesses  the  power 
of  liberating  the  oxygen  from  solutions  of  hydric  peroxide  H^O^.  This 
may  be  shown  by  dipping  a  few  shreds  of  fibrin  in  tincture  of  guaiacum 
and  tlien  immersing  them  in  a  solution  of  hydric  peroxide.  The  fibrin 
becomes  of  a  bluish  color,  from  its  having  liberated  from  the  solution 
oxygen,  which  oxidizes  the  resin  of  guaiacum  contained  in  the  tincture 
and  thus  produces  the  coloration. 


'  Tlio  \ise  of  the  two  words  albumen  and  albumin  mny  need  explanation.  The 
fornuir  is  Die  (leneric,  word  which  may  include  several  albuminous  or  i>rotoid  bodies, 
c.r/.,  albumen  of  blood;  the  latter,  which  requires  to  be  qualitied  by  another  word,  is 
the  spccidc  form,  and  is  jipjilied  to  variclics.  cj/.,  ci^g-albumin.  serum-albumin. 


THE  BLOOD.  85 

Salts  of  the  Plasma. — In  1000  parts  plasma  there  are:— 

Sodium  Chloride   5-540 

Soda   1*532 

Sodium  Phosphate   '271 

Potassium  chloride  .......  '359 

"        sulphate  ........  '281 

Calcium  phosphate       ......  '298 

Magnesium  phosphate    .       .       .       .       .       .  '218 


8.505 

Serum. — The  serum  is  the  liquid  part  of  the  blood  or  of  the  plasma 
remaining  after  the  separation  of  the  clot.  It  is  an  alkaline,  yellowish, 
transparent  fluid,  with  a  specific  gravity  of  from  1025  to  1032.  In  the 
usual  mode  of  coagulation,  part  of  the  serum  remains  in  the  clot,  and  the 
rest,  squeezed  from  the  clot  by  its  contraction,  lies  around  it.  Since  the 
contraction  of  the  clot  may  continue  for  thirty-six  or  more  hours,  the 
quantity  of  serum  in  the  blood  cannot  be  even  roughly  estimated  till  this 
period  has  elapsed.  There  is  nearly  as  much,  by  weight,  of  serum  as 
there  is  clot  in  coagulated  blood. 

Chemical  Composition  of  the  Serum. — 

Water  about 

Proteids: 

a.  Serum-albumin     .       .       .       .       .  ) 
Paraglobulin        .       .       .       .       .       .  j 

Salts. 

Fats — including  fatty  acids,  cholesterin,  lecithin; 
and  some  soaps  ....... 

Grape  sugar  in  small  amount  .... 

Extractives — kreatrn,  kreatinin,  urea,  etc.     .       .  > 

Yellow  pigment,  which  is  independent  of  haemo- 
globin ........ 

Gases — small  amounts  of  oxygen,  nitrogen,  and 
carbonic  acid  


1000 

Water. — The  water  of  the  serum  varies  in  amount  according  to  the 
amount  of  food,  drink,  and  exercise,  and  with  many  other  circumstances. 
Proteids. — a.  Serum-albumin  is  the  chief  proteid  found  in  serum. 

It  is  precipitated  on  heating  the  serum  to  140°  F.  (60°  C),  and 
entirely  coagulates  at  (167°  F.  75°  0.),  and  also  by  the  addition  of  strong 
acids,  such  as  nitric  and  hydrochloric;  by  long  contact  with  alcohol  it  is 
precipitated.  It  is  not  precipitated  on  addition  of  .ether,  and  so  differs 
from  the  other  native  albumin,  viz.,  e^/^/-albumin.  When  dried  at  104°F. 
(40°  0.)  serum-albumin  is  a  brittle,  yellowish  substance,  soluble  in  water, 
possessing  a  lasvo-rotary  power  of  — 56^.    It  is  with  great  difficulty 


900 
80 

20 


86 


HAND-BOOK  OF  PHYSIOLOaY. 


freed  from  its  salts,  and  is  precipitated  by  solutions  of  metallic  salts,  e.g. , 
of  mercuric  chloride,  copper  sulphate,  lead  acetate,  sodium  tungstate,  etc. 
If  dried  at  a  temperature  over  167°  F.  (75°  C.)  the  residue  is  insoluble 
in  water,  having  been  changed  into  coagulated  proteid. 

/?.  Paraglobulin  can  be  obtained  as  a  white  precipitate  from  cold  serum 
by  adding  a  considerable  excess  of  water  and  passing  through  it  a  current 
of  carbonic  acid  gas  or  by  the  cautious  addition  of  dilute  acetic  acid.  It 
can  also  be  obtained  by  saturating  serum  with  crystallized  sulphate  mag- 
nesium or  chloride  sodium.  When  obtained  in  the  latter  way  precipita- 
tion seems  to  be  much  more  complete  than  by  means  of  the  former 
method.    Paraglobulin  belongs  to  the  class  of  proteids  called  globulins. 

The  proportion  of  serum-albumin  to  paraglobulin  in  human  blood 
serum  is  as  1-511  to  1. 

The  salts  of  sodium  predominate  in  serum  as  in  plasma,  and  of  these 
the  chloride  generally  forms  by  far  the  largest  proportion. 

Fats  are  present  partly  as  fatty  acids  and  partly  emulsified.  The 
fats  are  triolein,  tristearin,  and  tripalmitin.  The  amount  of  fatty  matter 
varies  according  to  the  time  after,  and  the  ingredients  of,  a  meal.  Of 
cholesterin  and  lecithin  there  are  mere  traces. 

Grape  sugar  is  found  principally  in  the  blood  of  the  hepatic  vein, 
about  one  part  in  a  thousand. 

The  extractives  vary  from  time  to  time;  sometimes  uric  and  hip- 
puric  acids  are  found  in  addition  to  urea,  kreatin  and  kreatinin.  Urea 
exists  in  proportion  from  '02  to  '04  per  cent. 

The  yellow  pigment  of  the  serum  and  the  odorous  matter  which  gives 
the  blood  of  each  particular  animal  a  peculiar  smell,  have  not  yet  been 
properly  isolated. 

Variations  in"  healthy  Blood  ukder  different  Circumstakces. 

The  conditions  which  appear  most  to  influence  the  composition  of  the 
blood  in  health  are  these:  Sex,  Pregnancy,  Age,  and  Temperament.  The 
composition  of  the  blood  is  also,  of  course,  much  influenced  by  diet. 

1.  Sex. — The  blood  of  men  differs  from  that  of  women,  chiefly  in  be- 
ing of  somewhat  higher  specific  gravity,  from  its  containing  a  relatively 
larger  quantity  of  red  corpuscles. 

2.  Pregnancy. — The  blood  of  pregnant  women  has  a  ratlier  lower 
(Specific  gravity  than  the  average,  from  deficiency  of  red  corpuscles.  The 
(juantity  of  white  corj)Uscles,  on  the  other  hand,  and  of  fibrin,  is  in- 
creased. 

3.  Age. — It  appears  that  the  blood  of  the  foetus  is  very  rich  in  solid 
matter,  and  especially  in  red  corpuscles;  and  this  condition,  gradually 
diniinishing,  continues  for  some  weeks  after  birth.  The  quantity  of  solid 
matter  then  falls  during  childhood  below  the  average,  again  rises  during 
adult  life,  and  in  old  age  falls  again. 


THE  BLOOD. 


87 


4.  Temperament. — But  little  more  is  known  concerning  the  connection 
of  this  with  the  condition  of  the  blood,  than  that  there  appears  to  be  a 
relatively  larger  quantity  of  solid  matter,  and  particularly  of  red  corpuscles, 
in  those  of  a  plethoric  or  sanguineous  temperament. 

5.  Diet. — Such  differences  in  the  composition  of  the  blood  as  are  due  to 
the  temporary  presence  of  various  matters  absorbed  with  the  food  and 
drink,  as  well  as  the  more  lasting  changes  which  must  result  from  gener- 
ous or  poor  diet  respectively,  need  be  here  only  referred  to. 

Effects  of  Bleeding. — The  result  of  bleeding  is  to  diminish  the  specific 
gravity  of  the  blood;  and  so  quickly,  that  in  a  single  venesection,  the  portion 
of  blood  last  drawn  has  often  a  less  specific  gravity  than  that  of  the  blood 
that  flowed  first.  This  is,  of  course,  due  to  absorption  of  fluid  from  the 
tissues  of  the  body.  The  physiological  import  of  this  fact,  namely,  the 
instant  absorption  of  liquid  from  the  tissues,  is  the  same  as  that  of  the 
intense  thirst  which  is  so  common  after  either  loss  of  blood,  or  the  ab- 
straction from  it  of  watery  fluid,  as  in  cholera,  diabetes,  and  the  like. 

For  some  littlQ  time  after  bleeding,  the  want  of  red  corpuscles  is  well 
marked;  but  with  this  exception,  no  considerable  alteration  seems  to  be 
produce^  in  the  composition  of  the  blood  for  more  than  a  very  short  time: 
the  loss  of  the  other  constituents,  including  the  pale  corpuscles,  being 
very  quickly  repaired. 

VaEIATIONS  IK  THE  COMPOSITIOI^"  OF  THE  BlOOD,        DIFFERENT  PaRTS 

OF  THE  Body. 

The  composition  of  the  blood,  as  might  be  expected,  is  found  to  vary 
in  different  parts  of  the  body.  Thus  arterial  blood  differs  from  venous; 
and  although  its  composition  and  general  characters  are  uniform  through- 
out the  whole  course  of  the  systemic  arteries,  they  are  not  so  throughout 
the  venous  system, — the  blood  contained  in  some  veins  differing  remarka- 
bly from  that  in  others. 

Differences  between  Arterial  and  Venous  Blood. — The  differ- 
ences between  arterial  and  venous  blood  are  these: — 

(«.)  Arterial  blood  is  bright  red,  from  the  fact  that  almost  all  its 
haemoglobin  is  combined  with  oxygen  (Oxyhgemoglobin,  or  scarlet  haemo- 
globin), while  the  purple  tint  of  venous  blood  is  due  to  the  deoxida- 
tion  of  a  certain  quantity  of  its  oxyhsemoglobin,  and  its  consequent  reduc- 
tion to  the  purple  variety  (Deoxidized,  or  purple  hemoglobin). 

(&.)  Arterial  blood  coagulates  somewhat  more  quickly. 

{c. )  Arterial  blood  contains  more  oxygen  than  venous,  and  less  carbonic 
acid. 

Some  of  the  veins  contain  blood  which  differs  from  the  ordinary  stand- 
ard considerably.  These  are  the  Portal,  the  Hepatic,  and  the  Splenic 
veins. 

Portal  vein. — The  blood  which  the  portal  vein  conveys  to  the  liver  is 
supplied  from  two  chief  sources;  namely,  that  in  the  gastric  and  mesen- 
teric veins,  which  contains  the  soluble  elements  of  food  absorbed  from  the 


88 


HAND-BOOK  OF  rHYSlOLOGY. 


stomach  and  intestines  during  digestion,  ^md  that  in  the  splenic  vein;  it 
must,  therefore,  combine  the  qualities  of  the  blood  from  each  of  these 
sources. 

The  blood  in  the  gastric  and  mesenteric  veins  will  vary  much  accord- 
ing to  the  stage  of  digestion  and  the  nature  of  the  food  taken,  and  can 
therefore  be  seldom  exactly  the  same.  Speaking  generally,  and  without 
considering  the  sugar,  dextrin,  and  other  soluble  matters  which  may  have 
been  absorbed  from  the  alimentary  canal,  this  blood  appears  to  be  defi- 
cient in  solid  matters,  especially  in  red  corpuscles,  owing  to  dilution  by  the 
quantity  of  water  absorbed,  to  contain  an  excess  of  albumin,  and  to  yield 
a  less  tenacious  kind  of  fibrin  than  that  of  blood  generally. 

The  blood  from  the  splenic  vein  is  generally  deficient  in  red  corpuscles, 
and  contains  an  unusually  large  proportion  of  proteids.  The  fibrin  ob- 
tainable from  the  blood  seems  to  vary  in  relative  amount,  but  to  be  almost 
always  above  the  average.  The  proportion  of  colorless  corpuscles  is  also 
unusually  large.  The  whole  quantity  of  solid  matter  is  decreased,  the 
diminution  appearing  to  be  chiefly  in  the  proportion  of  red  corpuscles. 

The  blood  of  the  portal  vein,  combining  the  peculiarities  of  its  two 
factors,  the  splenic  and  mesenteric  venous  blood,  is  usually  of  lower 
specific  gravity  than  blood  generally,  is  more  watery,  contains  fewer  red 
corpuscles,  more  proteids,  and  yields  a  less  firm  clot  than  that  yielded  by 
other  blood,  owing  to  the  deficient  tenacity  of  its  fibrin. 

Guarding  (by  ligature  of  the  portal  vein)  against  the  possibility  of  an 
error  in  the  analysis  from  regurgitation  of  hepatic  blood  into  the  portal 
vein,  recent  observers  have  determined  that  hepatic  venous  Uoocl  contains 
less  water,  albumen,  and  salts,  than  the  blood  of  the  portal  vein;  but  that 
it  yields  a  much  larger  amount  of  extractive  matter,  in  which  is  one  con- 
stant element,  namely,  grape-sugar,  which  is  found,  whether  saccharine 
or  farinaceous  matter  have  been  present  in  the  food  or  not. 


The  Gases  of  the  Blood. 

The  gases  contained  in  the  blood  are  Carbonic  acid.  Oxygen,  and  Nitro- 
gen, 100  volumes  of  blood  containing  from  50  to  60  volumes  of  these  gases 
collectively. 

Arterial  blood  contains  relatively  more  ox3^gen  and  less  carbonic  acid 
than  venous.  But  the  absolute  quantity  of  carbonic  acid  is  in  both  kinds 
of  blood  greater  than  that  of  the  oxygen. 

Oxygen.              Carbonic  Acid.  Nitroo-en. 

Arterial  Blood  .  .  20  vol.  ^ler  cent.  39  vol.  per  cent.  1  to  2  vols. 
Venous  " 

(from  muscles  at  rest)  8  to  12  "   "    "  40    "   "  1  to  2  vols. 

The  Extraction  of  tlie  Gases  from  the  lUood. — As  the  ordinary  air- 
])umps  are  not  sufficiently  powerful  for  the  puri)ose,  the  extraction  of  the 
gases  from  the  blood  is  accomplisiied  by  means  of  a  mercurial  air-i)um]), 
of  wliich  there  are  many  varieties,  those  of  Ludwig,  Alvcrgnidt,  Geissler, 
and  Si)rengel  being  the  chief.    The  principle  of  action  in  all  is  much  the 


THE  BLOOD. 


89 


same.  Ludwig's  pump,  which  may  be  taken  as  a  type,  is  represented  in 
the  figure.  It  consists  of  two  fixed  globes,  C  and  F,  the  upper  one  com- 
municating by  means  of  the  stopcock  D,  and  a  stout  india-rubber  tube 
with  another  glass  globe,  L,  which  can  be  raised  or  lowered  by  means  of 
a  pulley;  it  also  communicates  by  means  of  a  stop-cock,  B,  and  a  bent 
glass  tube.  A,  with  a  gas  receiver  (not  represented  in  the  figure),  A  dip- 
ping into  a  bowl  of  mercury,  so  that  the  gas  may  be  received  over  mercury. 
The  lower  globe,  F,  communicates  with  C  by  means  of  the  stopcock,  E, 
with  /  in  which  the  blood  is  contained  by  the 
■stopcock  G,  and  with  a  movable  glass  globe, 
M,  similar  to  L.  by  means  of  the  stopcock,  H, 
and  the  stout  india-rubber  tube,  K. 

In  order  to  work  the  pump,  L  and  M  are 
■filled  with  mercury,  the  blood  from  which  the 
gases  are  to  be  extracted  is  placed  in  the  bulb 
I,  the  stopcocks,  H,  E,  D,  and  B,  being  open, 
and  G  closed.  M  is  raised  by  means  of  the 
pulley  until  F  is  full  of  mercury,  and  the  air 
is  driven  out.  E  is  then  closed,  and  L  is  raised 
so  that  C  becomes  full  of  mercury,  and  the  air 
driven  off.  B  is  then  closed.  On  lowering  L 
the  mercury  runs  into  it  from  G,  and  a  vacuum 
is  established  in  G.  On  opening  E  and  lower- 
ing M,  a  vacuum  is  similarly  established  in  i^; 
if  G  be  now  opened,  the  blood  in  /  will  enter 
into  ebullition,  and  the  gases  will  pass  off  into 
F  and  (7,  and  on  raising  M  and  then  L,  the 
stopcock  B  being  opened,  the  gas  is  driven 
through  A,  and  is  received  into  the  receiver 
over  mercury.  By  repeating  the  experiment 
several  times  the  whole  of  the  gases  of  the  speci- 
men of  blood  is  obtained,  and  may  be  estimated. 

The  Oxygen  of  the  Blood. — It  has  been 
found  that  a  very  small  proportion  of  the  oxygen  ^^•~^p^|'^  Mercurial 

which  can  be  obtained,  by  the  aid  of  the  mer- 
curial pump,  from  the  blood,  exists  in  a  state  of  simple  solution  in  the 
plasma.  If  the  gas  were  in  simple  solution,  the  amount  of  oxygen  in  any 
given  quantity  of  blood  exposed  to  any  given  atmosphere  ought  to  vary 
with  the  amount  of  oxygen  contained  in  the  atmosphere.  Since,  speak- 
ing generally,  the  amount  of  any  gas  absorbed  by  a  liquid  such  as  plasma 
would  depend  upon  the  proportion  of  the  gas  in  the  atmosphere  to  which 
the  liquid  was  exposed  —  if  the  proportion  were  great,  the  absorption 
would  be  great;  if  small,  the  absorption  would  be  similarly  small.  The 
absorption  would  continue  until  the  proportion  of  the  gas  in  the  liquid 


90 


HAND-BOOK  OF  PHYSIOLOGY, 


and  in  the  atmosphere  became  equal.  Other  things  would,  of  course,  in- 
fluence the  absorption,  such  as  the  kind  of  gas  employed,  nature  of  the 
liquid,  and  the  temperature  of  both,  but  cmteris  paribus,  the  amount  of 
a  gas  which  a  liquid  absorbs  depends  upon  the  proportion  of  the  gas — the 
so-called  partial  pressure — of  the  gas  in  the  atmosphere  to  which  the 
liquid  is  subjected.  And  conversely,  if  a  liquid  containing  a  gas  in  solu- 
tion be  exposed  to  an  atmosphere  containing  none  of  the  gas,  the  gas  will 
be  given  up  to  the  atmosphere  until  its  amount  in  the  liquid  and  in  the 
atmosphere  becomes  equal.  This  condition  is  called  a  condition  of  equal 
tensions.  The  condition  may  be  understood  by  a  simple  illustration.  A 
large  amount  of  carbonic  acid  gas  is  dissolved  in  a  bottle  of  water  by  ex- 
posing the  liquid  to  extreme  pressure  of  the  gas,  and  a  cork  is  placed  in 
the  bottle  and  wired  down.  The  gas  exists  in  the  water  in  a  condition  of 
extreme  tension,  and  therefore  there  is  a  tendency  of  the  gas  to  escape 
into  the  atmosphere,  in  order  that  the  tension  may  be  relieved ;  this  causes 
the  violent  expulsion  of  the  cork  when  the  wire  is  removed,  and  if  the 
water  be  placed  in  a  glass  the  gas  will  continue  to  be  evolved  until  it  is 
almost  all  got  rid  of,  and  the  tension  of  the  gas  in  the  water  approximates 
to  that  of  the  atmosphere  in  which,  it  should  be  remembered,  the  carbon 
dioxide  is,  naturally,  in  very  small  amount,  viz.,  -04  per  cent.  Now  the 
oxygen  of  the  blood  does  not  obey  this  law  of  pressure.  For  if  blood 
which  contains  little  or  no  oxygen  be  exposed  to  a  succession  of  atmos- 
pheres containing  more  and  more  of  that  gas,  we  find  that  the  absorption 
is  at  first  very  great,  but  soon  becomes  relatively  very  small,  not  being 
therefore  regularly  in  proportion  to  the  increased  amount  (or  tension) 
of  the  oxygen  of  the  atmospheres,  and  that  conversely,  if  arterial  blood  be 
submitted  to  regularly  diminishing  pressures  of  oxygen,  at  first  very  little 
of  the  contained  oxygen  is  given  ofi  to  the  atmosphere,  then  suddenly 
the  gas  escapes  with  great  rapidity,  again  disobeying  the  law  of  pres- 
sures. 

Very  little  oxygen  can  be  obtained  from  serum  freed  from  blood  cor- 
puscles, even  by  the  strongest  mercurial  air-pump,  neither  can  serum  be 
made  to  absorb  a  large  quantity  of  that  gas;  but  the  small  quantity  which 
is  so  given  up  or  so  absorbed  follows  the  laws  of  absorption  according  to 
pressure. 

It  must  be,  therefore,  evident  that  the  chief  part  of  the  oxygen  is  con- 
tained in  the  corpuscles,  and  not  in  a  state  of  simple  solution.  The  chief 
solid  constituent  of  the  colored  corpuscles  is  hmnioglobin,  which  consti- 
tutes more  tlian  90  per  cent,  of  their  bulk.  This  body  has  a  very  re- 
\l'  markable  aftinity  for  oxygen,  absorbing  it  to  a  very  definite  extent  under 
favorable  circumstances,  and  giving  it  up  when  subjected  to  the  action 
of  reducing  agents,  or  to  a  sufficiently  low  oxygen  pressure.  From  these 
facts  it  is  inferred  tliat  tlie  oxygen  of  the  blood  is  combined  with  hjpmo- 
globin,  and  not  simply  dissolved;  but  inasmuch  as  it  is  comparatively  easy 


THE  BLOOD. 


91 


to  cause  the  haemoglobin  to  give  up  its  oxygen,  it  is  believed  tliat  the 
oxygen  is  but  loosely  combined  with  the  substance. 

Haemoglobin. — Hi^moglobin  is  a  crystallizable  body  which  constitutes 
by  far  the  largest  portion  of  the  colored  corpuscles.  It  is  intimately  dis- 
tributed throughout  their  stroma,  and  must  be  dissolved  out  of  it  before 
it  will  undergo  crystallization.  Its  percentage  composition  is  C.  53-85; 
H.  7-32;  N.  16-17;  0.  21-84;  S.  -63;  Fe.  -42;  and  if  the  molecule  be  sup- 
posed to  contain  one  atom  of  iron  the  formula  would  be  0^^^^,  Ilgg^,  Nj^^, 
Fe  S3,  Oj^g.  The  most  interesting  of  the  properties  of  haemoglobin  are  its 
powers  of  crystallizing  and  its  attraction  for  oxygen  and  other  gases. 

Crystals. — The  haemoglobin  of  the  blood  of  various  animals  possesses 
the  power  of  crystallizing  to  very  different  extents  (blood-crystals).  In  some 
animals  the  formation  of  crystals  is  almost  spontaneous,  whereas  in  others 
crystals  are  formed  either  with  great  difficulty  or  not  at  all.  Among  the 
animals  whose  blood  coloring-matter  crystallizes  most  readily  are  the 
guinea-pig,  rat,  squirrel,  and  dog;  and  in  these  cases  to  obtain  crystals  it 
is  generally  sufficient  to  dilute  a  drop  of  recently-drawn  blood  with  water 
and  expose  it  for  a  few  minutes  to  the  air.  Light  seems  to  favor  the  for- 
mation of  the  crystals.  In  many  instances  oth  ^r  means  must  be  adopted, 
e.g.,  the  addition  of  alcohol,  ether,  or  chloroform,  rapid  freezing,  and 
then  thawing,  an  electric  current,  a  temperature  of  140°  F.  (60°  C),  or 
the  addition  of  sodium  sulphate. 

Human  blood  crystallizes  with  difficulty,  as  does  also  that  of  the  ox, 
the  pig,  the  sheep,  and  the  rabbit. 


Fia.  81.— Crystals  of  oxy-hsemoglobin— prismatic  from  human  blood. 

The  forms  of  haemoglobin  crystals,  as  will  be  seen  from  the  appended 
figures,  differ  greatly. 

Haemogloblin  crystals  are  soluble  in  water.  Both  the  crystals  them- 
selves and  also  their  solutions  have  the  characteristic  color  of  arterial 
blood. 


92 


HAND-BOOK  OF  PHYSIOLOGY. 


A  dilute  solution  of  liaemoglobin  gives  a  characteristic  appearance  with 
the  spectroscope.  Two  absorption  bands  are  seen  between  the  solar  lines 
D  and  E  (see  Plate),  one  toward  the  red,  with  its  middle  line  some  little 
way  to  the  blue  side  of  is  yery  intense,  but  narrower  than  the  other, 
which  lies  near  to  the  red  side  of  e.  Each  band  is  darkest  in  the  middle 
and  fades  away  at  the  sides.  As  the  strength  of  the  solution  increases  the 
bands  become  broader  and  deeper,  and  both  the  red  and  the  blue  ends  of 
the  spectrum  become  encroached  upon  until  the  bands  coalesce  to  form 
one  very  broad  band,  and  only  a  slight  amount  of  the  green  remains  un- 
absolved, and  part  of  the  red,  and  on  further  increase  of  strength  the 
former  disappears. 

If  the  crystals  of  oxy-hsemoglobin  be  subjected  to  a  mercurial  air-pump 
they  give  off  a  definite  amount  of  oxygen  (1  gramme  giving  off  1-59 


Fig.  82.— Oxj'-hsemoglobin  crystals — tetrahedral,  from  blood  of  the  guinea-pig. 
Fig.  83.— Hexagonal  oxy-haemoglobin  crystals,  from  blood  of  squirrel.    On  these  hexagonal 
plates,  prismatic  crystals,  grouped  in  a  stellate  manner,  not  unf requently  occur  (after  Fuuke). 

c.cm.  of  oxygen),  and  they  become  of  a  purple  color;  and  a  solution  of  oxy- 
ha?moglobin  may  be  made  to  give  up  oxygen  and  to  become  purple  in  a 
similar  manner. 

This  change  may  be  also  effected  by  passing  through  it  liydrogen  or 
nitrogen  gas,  or  by  the  action  of  reducing  agents,  of  which  Stokes^s  fluid' 
is  the  most  convenient. 

With  the  spectroscope  a  soltition  of  deoxidized  hjemoglobin  is  found 
to  give  an  entirely  different  appearance  from  that  of  oxidized  luvmoghv 
bin.  Instead  of  the  two  bands  at  D  and  E  we  find  a  single  broader  but 
fainter  band  occupying  a  position  midway  between  ihe  two,  and  at  the 


'  Sfoken\><  Fluid  consists  of  a  solution  of  fcrrot/K  HuljiJutfe,  to  Avliich  ammonia  has 
been  added  and  suflirient  tartaric  acid  to  prevent  precipitation.  Another  reducing: 
a«!^ent  ia  a  solution  of  stannous  chloride,  treated  in  a  way  similar  to  the  ferrous  sulphate, 
nu(\  a  third  nmsxent  of  like  nature  is  an  a(iu('ous  solution  of  ammonium  sulphide. 


Fig.  82. 


Fig.  83. 


THE  BLOOD. 


93 


same  time  less  of  the  blue  end  of  the  spectrum  is  absorbed.  Even  in 
strong  solutions  this  latter  appearance  is  found,  thereby  differing  from 
the  strong  solution  of  oxidized  haemoglobin  which  lets  through  only  the 
red  and  orange  rays;  accordingly  to  the  naked  eye  the  one  (reduced 
haemoglobin  solution)  appears  purple,  the  other  (oxy-haemoglobin  solu- 
tion) red.  The  deoxidized  crystals  or  their  solutions  quickly  absorb  oxy- 
gen on  exposure  to  the  air,  becoming  scarlet.  If  solutions  of  blood  be 
taken  instead  of  solutions  of  haemoglobin,  results  similar  to  the  whole  of 
the  foregoing  can  be  obtained. 

Venous  blood  neVer,  except  in  the  last  stages  of  asphyxia,  fails  to 
show  the  oxy-haemoglobin  bands,  inasmuch  as  the  greater  part  of  the 
haemoglobin  even  in  venous  blood  exists  in  the  more  highly  oxidized 
condition. 

Action  of  Gases  on  Haemoglobin. — Carlonic  o:?;^(^e,  passed  through 
a  solution  of  haemoglobin,  causes  it  to  assume  a  bluish  color,  and  the  spec- 
trum is  slightly  altered;  two  bands  are  still  visible,  but  are  somewhat 
nearer  the  blue  end  than  those  of  oxy-haemoglobin  (see  Plate).  The 
amount  of  carbonic  oxide  is  equal  to  the  amount  of  the  oxygen  displaced. 
Although  the  carbonic  oxide  gas  readily  displaces  oxygen,  the  reverse  is 
not  the  case,  and  upon  this  property  depends  the  dangerous  effect  of  coal 
gas  poisoning.  Coal  gas  contains  much  carbonic  oxide,  and  this  at  once, 
when  breathed,  combines  with  the  haemoglobin  of  the  blood,  producing 
a  compound  which  cannot  easily  be  reduced,  and  since  it  is  by  no  means 
an  oxygen  carrier,  death  may  result  from  suffocation  from  want  of  oxygen 
notwithstanding  the  free  entry  into  the  lungs  of  pure  air.  Crystals  of 
carbonic-oxide  haemoglobin  closely  resemble  those  of  oxyhaemoglobin. 

Nitric  oxide  produces  a  similar  compound  to  the  carbonic-oxide  haemo- 
globin, which  is  even  less  easily  reduced. 

Nitrous  oxide  reduces  oxyhaemoglobin,  and  therefore  leaves  the  reduced 
haemoglobin  in  a  condition  to  actively  take  up  oxygen. 

Sulphuretted  Hydrogen. — If  this  gas  be  passed  through  a  solution  of 
oxyhaemoglobin,  the  haemoglobin  is  reduced  and  an  additional  band 
appears  in  the  red.  If  the  solution  be  then  shaken  with  air,  the  two 
bands  of  oxyhemoglobin  replace  that  of  reduced  haemoglobin,  but  the 
band  in  the  red  persists. 

Pkoducts  of  the  Decomposition  of  Hemoglobin. 

Methaemoglobin. — If  an  aqueous  solution  of  oxyhsemoglobin  be 
exposed  to  the  air  for  some  time,  its  spectrum  undergoes  a  change;  the 
two  D  and  E  bands  become  faint,  and  a  new  line  in  the  red  at  c  is  devel- 
oped. The  solution,  too,  has  become  brown  and  acid  in  reaction,  and  is 
precipitable  by  basic  lead  acetate.  This  change  is  due' to  the  decomposi- 
tion of  haemoglobin,  and  to  the  production  of  metlKBmoglolin,    On  add- 


94 


HAOT)-BOOK  OF  PHYSIOLOGY. 


ing  ammonium  sulphide,  reduced  haemoglobin  is  produced,  and  on  shaking 
this  up  with  air,  oxyhgemogiobin  is  reproduced. 

Haematin. — By  the  action  of  heat,  or  of  acids  or  alkalies  in  the  pres- 
ence of  oxygen,  hasmoglobin  can  be  split  up  into  a  substance  called 
Hcematin,  which  contains  all  the  iron  of  the  haemoglobin  from  which  it 
was  derived,  and  a  proteid  residue.  Of  the  latter  it  is  impossible  to  say 
more  than  that  it  is  probably  made  up  of  one  or  more  bodies  of  the  globu- 
lin class.  If  there  be  no  oxygen  present,  instead  of  haematin  a  body  called 
hcamochromogen  is  produced,  which,  however,  will  speedily  undergo  oxi- 
dation into  haematin. 

Haematin  is  a  dark  brownish  or  black  non-crystallizable  substance  of 
metallic  lustre.  Its  percentage  composition  is  C.  64-30;  H.  5*50;  N.  9*06; 
Fe,  8-82;  0. 12-32;  which  gives  the  formula  C^^,  H,,,  1^^,  Fe,,  (Hoppe- 
Seyler).  It  is  •  insoluble  in  water,  alcohol,  and  ether;  soluble  in  the 
caustic  alkalies;  soluble  with  difficulty  in  hot  alcohol  to  which  is  added 
sulphuric  acid.  The  iron  may  be  removed  from  haematin  by  heating  it 
with  fuming  hydrochloric  acid  to  320°  F.  (160°  C),  and  a  new  body, 
Immatoporphyrm,  is  produced. 

In  acid  solution. — If  to  blood  an  excess  of  acetic  acid  be  added,  the 
color  alters  to  brown  from  decomposition  of  haemoglobin,  and  the  setting 
free  of  haematin;  by  shaking  this  solution  with  ether,  solution  of  the 
haematin  is  obtained.  The  spectrum  of  the  etherial  solution  shows  no 
less  than  four  absorption  bands,  viz.,  one  in  the  red  between  c  and  d,  one 
faint  and  narrow  close  to  D,  and  then  two  broader  bands,  one  between  d 
and  E,  and  another  nearly  midway  between  l  and  f.  The  first  band  is 
by  far  the  most  distinct,  and  the  acid  solution  of  haematin  without  ether 
shows  it  plainly. 

In  alkaline  solution. — The  absorption  band  is  still  in  the  red,  but 
nearer  to  d,  and  the  blue  end  of  the  spectrum  is  partially  absorbed  to  a 
considerable  extent.  If  a  reducing  agent  be  added,  two  bands  resembling 
those  of  oxyhemoglobin,  but  nearer  to  the  blue,  appear;  this  is  the  spec- 
trum of  reduced  Immatin.  On  shaking  the  reduced  ha?matin  with  air  or 
oxygen  the  two  bands  are  replaced  by  the  single  band  of  alkaline 
haematin. 

Haematoidin. — This  substance  is  found  in  tlie  form  of  yellowish 
crystals  in  old  blood  extravasations,  and  is  derived  from  the  ha?nioglobin. 
Their, crystalline  form  and  the  reaction  they  give  witli  nitric  acid  seem  to 
show  them  to  be  identical  with  Biliruhiu.  tlie  chief  coloring  matter  of 
the  Bile. 

Haemin. — One  of  the  most  important  derivatives  of  na^matin  is 
ITaimiii,  It  is  usually  called  llydrorhloratc  of  Ilanuafin  (or  hydrochlo- 
ride), but  its  exact  cliemical  composition  is  uncertain.  Its  formula  is  C,.^, 
II,„,  N„  Fe,,  0,„,  '2  llcl,  and  it  contains  5-18  per  cent,  of  chlorine,  but 
by  some  it  is  looked  upon  as  siini)ly  crystallized  luvmatin.  Although 


THE  BLOOD. 


95 


difficult  to  obtain  in  bulk,  a  specimen  may  be  easily  made  for  the  micro- 
scope in  the  following  way: — A  small  drop  of  dried  blood  is  finely  powdered 
with  a  few  crystals  of  common  salt  on  a  glass  slide,  and  spread  out;  a  cover 
glass  is  then  placed  upon  it,  and  glacial  acetic  acid  added  by  means  of  a 
capillary  pipette.  The  blood  at  once  turns  of  a  brownish  color.  The  slide 
is  then  heated,  and  the  acid  mixture  evaporated  to  dryness  at  a  high  tem- 
perature. The  excess  of  salt  is  washed  away  with  water  from  the  dried 
residue,  and  the  specimen  may  then  be  mounted.  A  large  number  of 
small,  dark,  reddish  black  crystals  of  a  rhombic  shape,  sometimes  ar- 
ranged in  bundles,  will  be  seen  if  the  slide  be  subjected  to  microscopic 
examination. 

The  formation  of  these  haemin  crystals  is  of  great  interest  and  impor- 
tance from  a  medico-legal  point  of  view,  as  it  constitutes  the  most  cer- 


tain and  delicate  test  we  have  for  the  presence  of  blood  (not  of  necessity 
the  blood  of  man)  in  a  stain  on  clothes,  etc.  It  exceeds  in  delicacy  even 
the  spectroscopic  test. 

Estimation  of  Haemoglobin. — The  most  exact  method  is  by  the 
estimation  of  the  amount  of  iron  in  a  given  specimen  of  blood,  but  as  this 
is  a  somewhat  complicated  process,  a  method  has  been  proposed  which, 
though  not  so  exact,  has  the  advantage  of  simplicity.  This  consists  in 
comparing  the  color  of  a  given  small  amount  of  diluted  blood  with  gly- 
cerine jelly  tinted  with  carmine  and  picrocarmine  to  represent  a  standard 
solution  of  blood  diluted  one  hundred  times.  The  amount  of  dilution 
which  the  given  blood  requires  will  thus  approximately  represent  the 
quantity  of  haemoglobin  it  contains.  (Gowers.) 

Distribution  of  Haemoglobin. — In  connection  with  the  ascertained 
function  of  haemoglobin  as  the  great  oxygen-carrier,  the  following  facts 
with  regard  to  its  distribution  are  of  importance. 

It  occurs  not  only  in  the  red  blood-cells  of  all  Vertebrata  (except  one 
fish  (leptocephalus)  whose  blood-cells  are  all  colorless),  but  also  in  similar 
cells  in  many  Worms:  moreover,  it  is  found  diffused  in  the  vascular  fluid 
of  some  other  worms  and  certain  Crustacea;  it  also  occurs  in  all  the  striated 
muscles  of  Mammals  and  Birds.    It  is  generally  absent  from  unstriated 


Fig.  84.— Haematoidin  crystals.  (Frey.) 


Fig.  85. — Hsemin  crystals.  (Frey.) 


96 


HAND-BOOK  OF  PHYSIOLOGY. 


muscle  except  that  of  tlie  rectum.  It  has  also  been  found  in  Mollusca  in 
certain  muscles  which  are  specially  active,  viz.,  those  which  work  the  rasp- 
like tongue. 

In  the  muscles  of  Fish  it  has  hitherto  only  been  met  with  in  the  very 
active  muscle  which  moves  the  dorsal  fin  of  the  Hippocampus  (Eay  Lan- 
kester). 

The  Carbon  Dioxide  Gas  in  the  Blood. — Of  this  gas  in  the 
blood,  part  exists  in  a  state  of  simple  solution  in  the  serum,  and  the  rest 
in  a  state  of  weak  chemical  combination.  It  is  believed  that  the  latter 
is  combined  with  the  sodium  carbonate  in  a  condition  of  bicarbonate. 
Some  observers  consider  that  part  of  the  gas  is  associated  with  the  cor- 
puscles. 

The  Nitrogen  in  the  Blood. — 'It  is  believed  that  the  whole  of  the 
small  quantity  of  the  nitrogen  contained  in  the  blood  is  simply  dissolved 
in  the  fluid  plasma. 

DEYELOPMEIfT  OF  THE  BlOOD. 

The  first  formed  blood-corpuscles  of  the  human  embryo  differ  much 
in  their  general  characters  from  those  which  belong  to  the  later  periods 


Fift.  86.— Part  of  the  network  of  developing  blood-vessels  in  the  vascular  area  of  a  guinea-pig. 
hi,  blood  corpuscles  becoming  free  in  an  enlarged  and  hollowed  out  pai-t  of  the  network;  a,  process 
of  protoplasm.   (E.  A.  Schiifer.) 

of  intra-uterine,  and  to  all  periods  of  extra-uterine  life.  Their  manner  of 
origin  is  at  first  very  simple. 

Surrounding  the  early  embryo  is  a  circular  area,  called  the  vascular 
area,  in  which  the  first  rudiments  of  the  blood-vessels  and  blood-corpuscles 
are  developed.  Here  the  nucleated  embryonal  cells  of  the  mesoblast,  from 
which  the  blood-vessels  and  corpuscles  are  to  be  formed,  send  out  processes 
in  various  directions,  and  these  joining  together,  form  an  irregular 
meshwork.  "^I'lie  nuclei  increase  in  number,  and  collect  chiefly  in  the 
larger  masses  of  protoi)lasm,  but  partly  also  in  the  im)cesses.  Tlieso 
nuclei  gather  around  them  a  certain  amount  of  tlie  protoplasm,  and  be- 


TlIE  BLOOD. 


97 


coming  colored,  form  tlie  red  blood  corpuscles.  The  protoplasm  of  the 
cells  and  their  branched  network  in  which  these  corpuscles  lie  then  be- 
comes hollowed  out  into  a  system  of  canals  enclosing  fluid,  in  which  the 
red  nucleated  corpuscles  float.    The  corpuscles  at  first  are  from  about 

^"gW  ^0  TiVo"  of  i^^^  diameter,  mostly  spherical,  and  with  granular 
contents,  and  a  well-marked  nucleus.    Their  nuclei,  which  are  about 

g-Jy-g-  of  an  inch  in  diameter,  are  central,  circular,  very  little  prominent 
on  the  surfaces  of  the  corpuscle,  and  apparently  slightly  granular  or  tu- 
berculated. 

The  corpuscles  then  strongly  resemble  the  colorless  corpuscles  of  the 
fully  developed  blood,  but  are  colored.  They  are  capable  of  amoeboid 
movement  and  multiply  by  division. 

When,  in  the  progress  of  embryonic  development,  the  liver  begins  to 
be  formed,  the  multiplication  of  blood-cells  in  the  whole  mass  of  blood 
ceases,  and  new  blood-cells  are  produced  by  this  organ,  and  also  by  the 
lymphatic  glands,  thymus  and  spleen.  These  are  at  first  colorless  and 
nucleated,  but  afterward  acquire  the  ordinary  blood- tinge,  and  resemble 
very  much  those  of  the  first  set.  They  also  multiply  by  division.  In 
whichever  way  produced,  however,  whether  from  the  original  formative 
cells  of  the  embryo,  or  by  the  liver  and  the  other  organs  mentioned 
above,  these  colored  nucleated  cells  begin  very  early  in  foetal  life  to  be 
mingled  with  colored  ??ow-nucleated  corpuscles  resembling  those  of  the 
adult,  and  at  about  the  fourth  or  fifth  month  of  embryonic  existence  are 
completely  replaced  by  them. 

Origin  of  the  Mature  Red  Corpuscles. — The  non-nucleated  red 
corpuscles  may  possibly  be  derived  from  the  nucleated,  but  in  all  proba- 
bility are  an  entirely  new  formation,  and  the  methods  of  their  origin  are 


Fig.  87.— Development  of  red  corpuscles  in  connective-tissue  cells.  From  the  subcutaneous  tissue 
of  a  new-born  rat.  h,  a  cell  containing  haemoglobin  in  a  diffused  form  in  the  protoplasm ;  h',  one  con- 
taining colored  globules  of  varying  size  and  vacuoles;  /i",  a  cell  filled  with  colored  globules  of  nearly- 
uniform  size;  /,  /',  developing  fat  cells.   (E.  A.  Schafer.) 

the  following: — (1.)  During  foetal  life  and  possibly  in  some  animals,  e.g., 
the  rat,  which  are  born  in  an  immature  condition,  for  some  little  time  after 
birth,  the  blood  discs  arise  in  the  connective  tissue  cells  in  the  following 
way.  Small  globules,  of  varying  size,  of  coloring  matter  arise  in  the 
protoplasm  of  the  cells,  and  the  cells  themselves  become  branched,  their 
branches  joining  the  branches  of  similar  cells.  The  cells  next  become 
Vol.  L— 7. 


98 


HAND-BOOK  OF  PHYSIOLOGY. 


vacuolated,  and  the  red  globules  are  free  in  a  cavity  filled  with  fluid  (Fig. 
88);  by  the  extension  of  the  cavity  of  the  cells  into  their  processes  anas- 
tomosing vessels  are  produced,  which  ultimately  join  with  the  previously 
existing  vessels,  and  the  globules,  now  having  the  size  and  appearance  of 
the  ordinary  red  corpuscles,  are  passed  into  the  general  circulation.  This 
method  of  formation  is  called  intraceTlular  (Schafer). 


Fig.  88.— Further  development  of  blood-corpuscles  in  connective-tissue  cells  and  transformation 
of  the  latter  into  capillary  blood-vessels,  a,  an  elongated  cell  with  a  cavity  in  the  protoplasm  occu- 
pied by  fluid  and  by  blood-corpuscles  which  are  stiU  globular;  ft,  a  hoUow  ceU,  the  nucleus  of  which 
has  multiplied.  The  new  nuclei  ai  e  arranged  arovmd  the  wall  of  the  cavity,  thej^corpuscles  in  which 
have  now  become  discord;  c,  shows  the  modp  of  union  of  a  "hsemapoietic"  cell,  which,  in  this  in- 
stance, contains  only  one  corpuscle,  with  the  prolongation  ( 6Z)  of  a  previously  existing  vessel;  a  and 
c,  from  the  new-born  rat;  &,  from  the  foetal  sheep.   (E.  A.  Schafer.) 

(2.)  From  the  wliite  corpuscles. — The  belief  that  the  red  corpuscles  are 
derived  from  the  white  is  still  very  general,  although  no  new  evidence 
has  been  recently  advanced  in  favor  of  this  view.  It  is,  however,  uncer- 
tain whether  the  nucleus  of  the  white  corpuscle  becomes  the  red  corpus- 
cle, or  whether  the  whole  white  corpuscle  is  bodily  converted  into  the  red 
by  the  gradual  clearing  up  of  its  contents  with  a  disappearance  of  the 
nucleus.    Probably  the  latter  view  is  the  correct  one. 

flfg^gft®  ^  %  %  % 

Fia.  89.— Colored  nucleated  corpuscles,  from  the  red  marrow  of  the  guinea-pig.   (E.  A.  Schafer.) 

(3.)  From,  the  medulla  of  hones. — Red  corpuscles  are  to  a  very  large 
extent  derived  during  adult  life  from  the  large  ]xilo  cells  in  the  rod  mar- 
row of  bones,  especially  of  the  ribs  (Figs.  44,  89).  These  cells  become 
colored  from  the  formation  of  haemoglobin  chiefly  in  one  part  of  their 
protoplasm.  Tliis  colored  part  becomes  separated  from  the  rest  of  the 
col]  and  forms  a  rod  corpuscle,  being  at  first  cu})-shaped,  but  soon  taking  on 
tlie  normal  api)earance  of  the  matui-e  cor])uscle.    It  is  supposed  that  the 


THE  BLOOD. 


99 


protoplasm  may  grow  up  again  and  form  a  number  of  red  corpuscles  in  a 
similar  way. 

(4.)  From  the  tissue  of  the  spleen. — It  is  probable  that  red  as  well  as 
white  corpuscles  may  be  produced  in  the  spleen. 

(5.)  From  Microcytes. — Hayem  describes  the  small  particles  (micro- 
cytes),  previously  mentioned  as  contained  in  the  blood  (p.  75),  and  which 
he  calls  hsematoblasts,  as  the  precursors  of  the  red  corpuscles.  They  ac- 
quire color,  and  enlarge  to  the  normal  size  of  red  corpuscles. 

Without  doubt,  the  red  corpuscles  have,  like  all  other  parts  of  the 
organism,  a  tolerably  definite  term  of  existence,  and  in  a  like  manner  die 
and  waste  away  when  the  portion  of  work  allotted  to  them  has  been  per- 
formed. Neither  the  length  of  their  life,  however,  nor  the  fashion  of 
their  decay  has  been  yet  clearly  made  out.  It  is  generally  believed  that 
a  certain  number  of  the  red  corpuscles  undergo  disintegration  in  the 
spleen;  and  indeed  corpuscles  in  various  degrees  of  degeneration  have 
been  observed  in  this  organ. 

Origin  of  the  Colorless  Corpuscles.— The  colorless  corpuscles  of 
the  blood  are  derived  from  the  lymph  corpuscles,  being,  indeed,  indistin- 
guishable from  them;  and  these  come  chiefly  from  the  lymphatic  glands. 
Their  number  is  increased  by  division. 

Colorless  corpuscles  are  also  in  all  probability  derived  from  the  spleen 
and  thymus,  and  also  from  the  germinating  endothelium  of  serous  mem- 
branes, and  from  connective  tissue.  The  corpuscles  are  carried  into  the 
blood  either  with  the  lymph  and  chyle,  or  pass  directly  from  the  lymphatic 
tissue  in  which  they  have  been  formed  into  the  neighboring  blood-vessels. 

Uses  of  the  Blood. 

1.  To  be  a  medium  for  the  reception  and  storing  of  matter  (ordinary 
food,  drink,  and  oxygen)  from  the  outer  world,  and  for  its  conveyance  to 
all  parts  of  the  body. 

2.  To  be  a  source  whence  the  various  tissues  of  the  body  may  take  the 
materials  necessary  for  their  nutrition  and  maintenance;  and  whence 
the  secreting  organs  may  take  the  constituents  of  their  various  secretions. 

3.  To  be  a  medium  for  the  absorption  of  refuse  matters  from  all  the 
tissues,  and  for  their  conveyance  to  those  organs  whose  function  it  is  to 
separate  them  and  cast  them  out  of  the  body. 

4.  To  warm  and  moisten  all  parts  of  the  body. 

Uses  of  the  Various  Constituents  of  the  Blood. 

Albumen. — Albumen,  which  exists  in  so  large  a  proportion  among  the 
chief  constituents  of  the  blood,  is  without  doubt  mainly  for  the  nourish- 
ment of  those  textures  which  contain  it  or  other  compounds  nearly  allied 
to  it. 


100 


HAI^D-BOOK  OF  PHYSIOLOGY. 


Fibrin. — In  considering  the  functions  of  fibrin,  we  may  exclude  the 
notion  of  its  existence,  as  such,  in  the  blood  in  a  fluid  state,  and  of  its  use 
in  the  nutrition  of  certain  special  textures,  and  look  for  the  explanation 
of  its  functions  to  those  circumstances,  whether  of  health  or  disease, 
under  which  it  is  produced.  In  hsemorrhage,  for  example,  the  formation 
of  fibrin  in  the  clotting  of  blood,  is  the  means  by  which,  at  least  for  a 
time,  the  bleeding  is  restrained  or  stopped;  and  the  material  or  llastema 
which  is  produced  for  the  permanent  healing  of  the  injured  part,  con- 
tains a  coagulable  material  identical,  or  very  nearly  so,  with  the  fibrin  of 
clotted  blood. 

Fatty  matters. — The  fatty  matters  of  the  blood  subserve  more  than 
one  purpose.  For  while  they  are  the  means,  in  part,  by  which  the  fat  of 
the  body,  so  widely  distributed  in  the  proper  adipose  and  other  textures, 
is  replenished,  they  also,  by  their  union  with  oxygen,  assist  in  maintain- 
ing the  temperature  of  the  body.  To  certain  secretions  also,  notably  the 
milk  and  bile,  fat  is  contributed. 

Saline  Matter. — The  uses  of  the  saline  constituents  of  the  blood  are, 
first,  to  enter  into  the  composition  of  such  textures  and  secretions  as  natu- 
rally contain  them,  and,  secondly,  to  assist  in  preserving  the  due  specific 
gravity  and  alkalinity  of  the  blood,  and  in  preventing  its  decomposition. 
The  phosphate  and  carbonate  of  sodium,  to  which  the  blood  owes  its 
alkaline  reaction,  increase  the  absorptive  power  of  the  serum  for  gases. 

Corpuscles. — The  important  use  of  the  red  corpuscles  is  in  relation  to 
the  absorption  of  oxygen  in  the  lungs,  and  its  conveyance  to  the  tissues. 
How  far  the  red  corpuscles  are  actually  concerned  in  the  nutrition  of  the 
tissues  is  quite  unknown. 

The  relation  of  the  colorless  corpuscles  to  the  coagulation  of  the  blood 
has  been  already  considered;  of  their  functions,  other  than  are  concerned 
in  this  phenomenon,  and  in  the  regeneration  of  the  red  corpuscles, 
nothing  is  positively  known. 


CHAPTER  V. 


THE  CIRCULATION  OF  THE  BLOOD. 

The  Heart  is  a  hollow  muscular  organ  containing  four  chambers,  two 
auricles  and  two  ventricles,  arranged  in  pairs.  On  each  side  (right  and 
left)  of  the  heart  is  an  auricle  joined  to  and  communicating  with  a  ven- 
tricle, but  the  chambers  on  the  right  side  do  not  directly  communicate 
with  those  on  the  left  side.    The  circulation  of  the  blood  is  chiefly 


Fig.  90.— Diagram  of  the  Circulation. 


carried  on  by  the  contraction  of  the  muscular  walls  of  these  chambers  of 
the  heart,  the  auricles  contracting  simultaneously,  and  their  contraction 
being  followed  by  the  simultaneous  contraction  of  the  ventricles.  The 
blood  is  conveyed  away  from  the  left  side  of  the  heart  by  the  arteries, 
and  returned  to  the  right  side  of  the  heart  by  the  veins,  the  arteries  and 
veins  being  continuous  with  each  other  at  one  end  by  means  of  the  heart, 
and  at  the  other  by  a  fine  network  of  vessels  called  the  capillaries.  The 


102 


HAND-BOOK   OF  PHYSIOLOGY. 


blood,  therefore,  in  its  passage  from  the  heart  passes  first  into  the  arteries, 
then  into  the  capillaries,  and  lastly  into  the  veins,  by  which  it  is  con- 
veyed back  again  to  the  heart,  thus  completing  a  revolution  or  circulatiori. 

The  right  side  of  the  heart  does  not  directly  communicate  with  the 
left  to  complete  the  entire  circulation,  but  the  blood  has  to  pass  from  the 
right  side  to  the  lungs,  through  the  pulmonary  artery,  then  through  tlie 
pulmonary  capillary-vessels  and  through  the  pulmonary  veins  to  the  left 
side  of  the  heart.  Thus  there  are  two  circulations  by  which  the  blood 
must  pass;  the  one,  a  shorter  circuit  from  the  right  side  of  the  heart  to 
the  lungs  and  back  again  to  the  left  side  of  the  heart;  the  other  and 
larger  circuit,  from  the  left  side  of  the  heart  to  all  parts  of  the  body  and 
back  again  to  the  right  side;  but  more  strictly  speaking,  there  is  only  one 
complete  circulation,  which  may  be  diagrammatically  represented  by  a 
double  loop,  as  in  the  accompanying  figure  (Fig.  90). 


Diaphragm. 

Fig.  91.— View  of  heart  and  hings  in  situ.  The  front  portion  of  the  chest- wall,  and  the  outer  or 
parietal  layers  of  the  pleurae  and  pericardium  have  been  removed.   The  lungs  are  partly  collapsed. 

On  reference  to  this  figure,  and  noticing  the  direction  of  the  arrows, 
which  represent  the  course  of  the  stream  of  blood,  it  will  be  observed 
that  while  there  is  a  smaller  and  a  larger  circle,  both  of  which  pass 
through  the  heart,  yet  that  these  are  not  distinct,  one  from  the  other,  but 
are  formed  really  by  one  continuous  stream,  the  whole  of  which  must,  at 
one  part  of  its  course,  pass  through  the  lungs.  Subordinate  to  the  two 
principal  circulations,  the  Pulmmiary  and  Systemic,  as  they  are  named, 
it  will  be  noticed  also  in  the  same  figure  that  there  is  another,  by  which 
a  ])()rtion  of  the  stream  of  blood  having  been  diverted  once  into  the  cap- 
illaries of  the  intestinal  canal,  and  some  other  organs,  aiul  gathered  uj) 
again  into  a  single  stream,  is  a  second  time  divided  in  its  passage  through 


CIRCULATION  OF  THE  BLOOD.  103 

the  liver,  before  it  finally  reaches  the  heart  and  completes  a  revolution. 
This  subordinate  stream  through  the  liver  is  called  the  Portal  circulation. 
The  Forces  concerned  in  the  Circulation  of  the  Blood.— (1) 

The  principal  force  provided  for  constantly  moving  the  blood  through 
the  course  of  the  circulation  is  that  of  the  muscular  substance  of  the 
heart;  other  assistant  forces  are  (2)  those  of  the  elastic  walls  of  the  arte- 
ries, (3)  the  pressure  of  the  muscles  among  which  some  of  the  veins  run, 
(4)  the  movements  of  the  walls  of  the  chest  in  respiration,  and  probably, 
to  some  extent,  (5)  the  interchange  of  relations  between  the  blood  and 
the  tissues  which  occurs  in  the  capillary  system  during  the  nutritive 
processes. 

The  Heart. 

The  Pericardium. — The  heart  is  invested  by  a  membranous  sac — 
the  pericardium,  which  is  made  up  of  two  distinct  parts,  an  external 
fibrous  membrane,  composed  of  closely  interlacing  fibres,  which  has  its 
base  attached  to  the  diaphragm — both  to  the  central  tendon  and  to  the 
adjoining  muscular  fibres,  while  the  smaller  and  upper  end  is  lost  on  the 
large  blood-vessels  by  mingling  its  fibres  with  that  of  their  external  coats; 
and  an  iiiternal  serous  layer,  which  not  only  lines  the  fibrous  sac,  but  also 
is  reflected  on  to  the  heart,  which  it  completely  invests.  The  part  which 
lines  the  fibrous  membrane  is  called  the  parietal  layer,  and  that  enclosing 
the  heart,  the  visceral  layer,  and  these  being  continuous  for  a  short  distance 
along  the  great  vessels  of  the  base  of  the  heart,  form  a  closed  sac,  the 
cavity  of  which  in  health  contains  just  enough  fluid  to  lubricate  the  two 
surfaces,  and  thus  enable  them  to  glide  smoothly  over  each  other  during 
the  movements  of  the  heart.  Most  of  the  vessels  passing  in  and  out  of 
the  heart  receive  more  or  less  investment  from  this  sac. 

The  heart  is  situated  in  the  chest  behind  the  sternum  and  costal  car- 
tilages, being  placed  obliquely  from  right  to  left,  quite  two-thirds  to  the 
left  of  the  mid-sternal  line.  It  is  of  pyramidal  shape,  with  the  apex 
pointing  downward,  outward,  and  toward  the  left,  and  the  base  backward, 
inward,  and  toward  the  right.  It  rests  upon  the  diaphragm,  and  ijts 
pointed  apex,  formed  exclusively  of  the  left  side  of  the  heart,  is  in  con- 
tact with  the  chest  wall,  and  during  life  beats  against  it  at  a  point  called 
the  apex  teat,  situated  in  the  fifth  intercostal  space,  about  two  inches 
below  the  left  nipple,  and  an  inch  and  a  half  to  the  sternal  side.  The 
heart  is  suspended  in  the  chest  by  the  large  vessels  which  proceed  from 
its  base,  but,  excepting  the  base,  the  organ  itself  lies  free  in  the  sac  of 
the  pericardium.  The  part  which  rests  upon  the  diaphragm  is  flattened, 
and  is  known  as  the  posterior  surface,  whilst  the  free  upper  part  is  called 
the  anterior  surface.  The  margin  toward  the  left  is  thick  and  obtuse, 
whilst  the  lower  margin  toward  the  right  is  thin  and  acute. 


104 


HAND-BOOK  OF  PHYSIOLOGY. 


On  examination  of  the  external  surface  the  division  of  the  heart  into 
parts  which  correspond  to  the  chambers  inside  of  it  may  be  traced,  for  a 
deep  transverse  groove  called  the  auriculo-ventricular  groove  divides  the 
auricles  which  form  the  base  of  the  heart  from  the  ventricles  which  form 
the  remainder,  including  the  apex,  the  ventricular  portion  being  by  far 
the  greater;  and,  again,  the  inter-ventricular  groove  runs  between  the 


Fig.  92.— The  right  auricle  and  ventricle  opened,  and  a  part  of  their  right  and  anterior  •*ralls  re- 
moved, so  as  to  show  their  interior.  superior  vena  cava;  2.  inferior  vena  cava:  2\  hepatic 
veins  cut  short;  3,  right  auricle;  3'.  placed  in  the  fossa  ovalis,  below  which  is  the  Eustachian  valve; 
3",  is  placed  close  to  the  aperture  of  the  coronary  vein;  +.  +,  placed  in  the  auriculo-ventricular 
groove,  where  a  nai'row  portion  of  the  adjacent  walls  of  the  auricle  and  ventricle  has  been  preserved; 
4,  4,  cavity  of  the  right  ventricle,  the  upper  figiu-e  is  immediately  below  the  semilunar  valves;  4'. 
large  columna  carnea  or  muscuhis  papillaris;  5.  5'.  5",  tricuspid  valve;  G,  placed  in  the  interior  of  the 
pulmonary  artery,  a  part  of  tlie  anterior  wall  of  that  vessel  having  been  removed,  and  a  narrow  por- 
tion of  it  preserved  at  its  connuencemeut.  where  the  semilunar  valves  are  attached;  7,  concavity  of 
the  aortic  ai'ch  close  to  the  cord  of  the  ductus  arteriosus;  S.  ascending  part  or  sinus  of  the  arch  cov- 
ered at  its  commencement  by  the  auricular  appentlix  and  i)ulmonary  arterj-;  1),  placed  between  the 
innominate  and  left  carotid  arteries;  10,  appendix  of  the  left  auricle;  11,  11,  the  outside  of  the  left 
ventricle,  the  lower  figure  near  the  apex.   (.Allen  Thomson.) 

ventricles  botli  front  and  back,  and  separates  the  one  from  tlie  otlior. 
The  anterior  groove  is  nearer  the  left  margin  and  the  posterior  nearer  the 
right,  as  the  front  surface  of  tlie  heart  is  made  up  chiefly  of  the  right 
ventricle  and  the  posterior  surface  of  tlie  loft  ventricle.  In  the  furrows 
run  the  coronary  vessels,  which  sui)i)ly  the  tissue  of  the  heart  itself  with 
))l()()d,  as  well  as  nerves  and  lymphatics  imbedded  in  more  or  less  fatty 
tissue. 


CIRCULATIOI^  OF  THE  BLOOD. 


105 


The  Chambers  of  the  Heart. — The  interior  of  the  heart  is  divided 
by  a  partition  in  such  a  manner  as  to  form  two  chief  chambers  or  cavities 
— right  and  left.  Each  of  these  chambers  is  again  subdivided  into  an 
upper  and  a  lower  portion,  called  respectively,  as  already  incidentally  men- 
tioned, auricle  and  ventricle,  which  freely  communicate  one  with  the 
other;  the  aperture  of  communication,  however,  being  guarded  by  valves, 
so  disposed  as  to  allow  blood  to  pass  freely  from  the  auricle  into  the  ven- 
tricle, but  not  in  the  opposite  direction.  There  are  thus  four  cavities 
altogether  in  the  heart — two  auricles  and  two  ventricles;  the  auricle  and 
ventricle  of  one  side  being  quite  separate  from  those  of  the  other 
(Pig.  90). 

Right  Auricle. — The  right  auricle  is  situated  at  the  right  part  of 
the  base  of  the  heart  as  viewed  from  the  front.  It  is  a  thin  walled  cavity 
of  more  or  less  quadrilateral  shape  prolonged  at  one  corner  into  a  tongue- 
shaped  portion,  the  right  auricular  appendix,  which  slightly  overlaps  the 
exit  of  the  great  artery,  the  aorta,  from  the  heart. 

The  interior  is  smooth,  being  lined  with  the  general  lining  of  the 
heart,  the  endocardium^  and  into  it  open  the  superior  and  inferior  venae 
cavae,  or  great  veins,  which  convey  the  blood  from  all  parts  of  the  body 
to  the  heart.  The  former  is  directed  downward  and  forward,  the  latter 
upward  and  inward;  between  the  entrances  of  these  vessels  is  a  slight 
tubercle  called  tubercle  of  Lower.  The  opening  of  the  inferior  cava  is 
protected  and  partly  covered  by  a  membrane  called  the  Eustachian  valve. 
In  the  posterior  wall  of  the  auricle  is  a  slight  depression  called  the 
fossa  ovalis,  which  corresponds  to  an  opening  between  the  right  and  left 
auricles  which  exists  in  foetal  life.  The  right  auricular  appendix  is  of 
oval  form,  and  admits  three  fingers.  Various  veins,  including  the  cor- 
onary sinus,  or  the  dilated  portion  of  the  right  coronary  vein,  open  into 
this  chamber.  In  the  appendix  are  closely  set  elevations  of  the  muscular 
tissue  covered  with  endocardium,  and  on  the  anterior  wall  of  the  auricle 
are  similar  elevations  arranged  parallel  to  one  another,  called  musculi 
ipectinati. 

Right  Ventricle. — The  right  ventricle  occupies  the  chief  part  of  the  * 
anterior  surface  of  the  heart,  as  well  as  a  small  part  of  the  posterior  sur- 
face: it  forms  the  right  margin  of  the  heart.  It  takes  no  part  in  the 
formation  of  the  apex.  On  section  its  cavity,  in  consequence  of  the 
encroachment  upon  it  of  the  septum  ventriculorum,  is  semilunar  or  cre- 
scentic  (Fig.  94);  into  it  are  two  openings,  the  auriculo-ventricular  at 
the  base,  and  the  opening  of  the  pulmonary  artery  also  at  the  base,  but 
more  to  the  left;  the  part  of  the  ventricle  leading  to  it  is  called  the  comis 
arteriosus  or  infundihulum;  both  orifices  are  guarded  by  valves,  the 
former  called  tricuspid  and  the  latter  semilunar  or  sigmoid.  In  this 
ventricle  are  also  the  projections  of  the  muscular  tissue  called  columnce 
carnem  (described  at  length  p.  110). 


106 


HAND-BOOK  OF  PHYSIOLOGY. 


Left  Auricle. — The  left  auricle  is  situated  at  the  left  and  posterior 
part  of  the  base  of  the  heart,  and  is  best  seen  from  behind.  It  is  quadri- 
lateral, and  receives  on  either  side  two  pulmonary  veins.  The  auricular 
appendix  is  the  only  part  of  the  auricle  seen  from  the  front,  and  corre- 


Fig.  93.— The  left  auricle  and  ventricle  opened,  and  a  part  of  their  anterior  and  left  walls  re- 
moved. 1/^.— The  pulmonary  arterj-  has  been  divided  at  its  commencement;  the  opening  into  the  left 
ventricle  carried  a  short  distance  into  the  aorta  between  Uvo  of  the  segments  of  the  semilimar  valves, 
and  the  left  part  of  the  auricle  with  its  appendix  has  been  removed.  Tlie  right  auricle  is  out  of  view. 
•  1,  the  two  right  pulmonary  veins  cut  short;  their  openings  are  seen  within  the  auricle;  1',  placed 
within  the  cavity  of  the  auricle  on  the  left  side  of  the  septum  and  on  the  part  which  forms  tne  re- 
mains of  the  valve  of  the  foramen  ovale,  of  which  the  crescentic  fold  is  seen  toward  the  left  hand  of 
1';  2.  a  narrow  portion  of  the  wall  of  the  auricle  and  ventricle  pi  eserved  round  the  auriculo-ven- 
tricular  orifice;  3,  3',  the  cut  surface  of  the  walls  of  the  ventricle,  seen  to  become  veiy  much  thinner 
toward  3".  at  the  apex;  4,  a  small  part  of  the  anterior  wall  of  the  left  ventricle  which  has  been  pre- 
served with  the  principal  anterior  cohunna  carneaor  musculus  papillniis  attached  to  it;  5,  ,5,  nnisculi 
papillares;  5',  the  left  side  of  the  septum,  between  the  two  ventricles,  within  the  cavity  of  the  left 
ventricle;  0,  (>',  the  mitral  valve;  7,  placed  in  the  interior  of  the  aorta  near  its  commencement  and 
above  the  three  segments  of  its  semilunar  valve  which  are  hanging  loosely  together;  7',  the  exterior 
of  the  great  aortic  siinis;  8,  the  root  of  the  inilmonary  artery  and  its  semilunar  valves;  8',  the  sepa- 
rated portion  of  the  i)uhiionary  art<'ry  rcniaining  attacluHl  to  the  aorta  by  it,the  cord  of  the  ductus 
arteriosus;  10,  the  ai  tei  ies  rising  from  the  sunmiit  of  the  aortic  arch.  (Allen  Thomson.) 


spoiuls  with  that  on  the  right  side,  but  is  thicker,  and  tlie  interior  is  more 
smootli.  The  loft  auricle  is  only  slightly  thicker  than  the  right,  the  dif- 
ference being  as  lines  to  1  line.  The  left  auriculo-veutricular  orifice 
is  oval,  and  a  little  smaller  than  that  on  the  right  side  of  the  heart. 


CIRCULATION  OF  THE  BLOOD. 


107 


There  is  a  slight  vestige  of  the  foramen  between  the  auricles,  which 
exists  in  fcetal  life,  on  the  septum  between  them. 

Left  Ventricle.— Though  taking  part  to  a  comparatively  slight 
extent  in  the  anterior  surface,  the  left  ventricle  occupies  the  chief  part  of 
the  posterior  surface.  In  it  are  two  openings  very  close  together,  viz. 
the  auriculo-ventricular  and  the  aortic,  guarded  by  the  valves  corre- 
sponding to  those  of  the  right  side  of 
the  heart,  viz.  the  bicuspid  or  mitral 
and  the  semilunar  or  sigmoid.  The  first 
opening  is  at  the  left  and  back  part  of 
the  base  of  the  ventricle,  and  the  aortic 
in  front  and  toward  the  right.  In  this 
ventricle,  as  in  the  right,  are  the  co- 
lumnae  carneae,  which  are  smaller  but 

more     closely    reticulated.       They    are       Fxg.  94.— Transverse  section  of  bullock^s 
T  heart  in  a  state  of  cadaveric  rigidity,  a, 

chieiiy  round  near  the  apex  and  along   cavity  of  left  ventricle.  6,  cavity  of  right 

,     .  n  •^^   ^  •       ventricle.  (Dalton.) 

the  posterior  wall.    They  will  be  again 

referred  to  in  the  description  of  the  valves.  The  walls  of  the  left  ven- 
tricle, which  are  nearly  half  an  inch  in  thickness,  are,  with  the  exception 
of  the  apex,  twice  or  three  times  as  thick  as  those  of  the  right. 

Capacity  of  the  Chambers. — The  capacity  of  the  two  ventricles 
is  about  four  to  six  ounces  of  blood,  the  whole  of  which  is  impelled  into 
their  respective  arteries  at  each  contraction.  The  capacity  of  the  auricles 
is  rather  less  than  that  of  the  ventricles:  the  thickness  of  their  walls  is 
considerably  less.  The  latter  condition  is  adapted  to  the  small  amount 
of  force  which  the  auricles  require  in  order  to  empty  themselves  into  their 
adjoining  ventricles;  the  former  to  the  circumstance  of  the  ventricles 
being  partly  filled  with  blood  before  the  auricles  contract. 

Size  and  Weight  of  the  Heart. — The  heart  is  about  5  inches 
long,  3^  inches  greatest  width,  and  2^-  inches  in  its  extreme  thickness. 
The  average  weight  of  the  heart  in  the  adult  is  from  9  to  10  ounces;  its 
weight  gradually  increasing  throughout  life  till  middle  age;  it  diminishes 
in  old  age. 

Structure. — The  walls  of  the  heart  are  constructed  almost  entirely 
of  layers  of  muscular  fibres;  but  a  ring  of  connective  tissue,  to  which  some 
of  the  muscular  fibres  are  attached,  is  inserted  between  each  auricle  and 
ventricle,  and  forms  the  boundary  of  the  auriculo-ventricular  opening. 
Fibrous  tissue  also  exists  at  the  origins  of  the  pulmonary  artery  and  aorta. 

The  muscular  fibres  of  each  auricle  are  in  part  continuous  with  those 
of  the  other,  and  partly  separate;  and  the  same  remark  holds  true  for  the 
ventricles.  The  fibres  of  the  auricles  are,  however,  quite  separate  from 
those  of  the  ventricles,  the  bond  of  connection  between  them  being  only 
the  fibrous  tissue  of  the  auriculo-ventricular  openings. 

The  muscular  fibres  of  the  heart,  unlike  those  of  most  of  the  involun- 


108 


HAND-BOOK  OF  PHYSIOLOGY. 


tary  muscles,  are  striated;  but  although,  in  this  respect,  they  resemble 
the  skeletal  muscles,  they  have  distinguishing  characteristics  of  their  own. 
The  fibres  which  lie  side  by  side  are  united  at  frequent  intervals  by  short 
branches  (Fig.  95).  The  fibres  are  smaller  than  those  of  the  ordinary 
striated  muscles,  and  their  striation  is  less  marked.  No  sarcolemma  can 
be  discerned.  The  muscle-corpuscles  are  situate  in  the  middle  of  the 
substance  of  the  fibre;  and  in  correspondence  with  these  the  fibres  appear 
under  certain  conditions  subdivided  into  oblong  portions  or  cells,  the 
off-sets  from  which  are  the  means  by  which  the  fibres  anastomose  one 
with  another  (Fig.  96). 

Endocardium. — As  the  heart  is  clothed  on  the  outside  by  a  thin 
transparent  .layer  of  pericardium,  so  its  cavities  are  lined  by  a  smooth  and 


Fig.  95.  Fig.  96. 

Fig.  95. — Network  of  muscular  fibres  (striated")  from  the  heart  of  a  pig.   The  nuclei  of  the  mus- 
cle-corpuscles are  well  shown,    x  4.50.    (Klein  and  Noble  Smith.) 
Fig.  9fj.— Muscular  fibre  cells  from  the  heart.    (E.  A.  Shiifer.) 

shining  membrane,  or  endocardium,  which  is  directly  continuous  with  the 
internal  lining  of  the  arteries  and  veins.  The  endocardium  is  composed  of 
connective  tissue  with  a  large  admixture  of  elastic  fibres;  and  on  its  inner 
surface  is  laid  down  a  single  tessellated  layer  of  flattened  endothelial  cells. 
Here  and  there  unstriped  muscular  fibres  are  sometimes  found  in  the  tis- 
sue of  the  endocardium. 

Course  of  the  Blood  through  the  Heart. — The  arrangement  of 
the  heart's  valves  is  such  that  the  blood  can  pass  only  in  one  direction, 
and  this  is  as  follows  (Fig.  97): — From  the  riglit  auricle  the  blood  passes 
into  the  riglit  ventricle,  and  tlience  into  the  pnhuonary  artery,  by  wliich 
it  is  conveyed  to  the  capilhiries  of  the  lungs.  From  tlio  Inngs  the  blood, 
wliicli  is  now  purified  and  altered  in  color,  is  gathered  by  the  pulmonary 


CIRCULATION  OF  THE  BLOOD. 


109 


veins  and  taken  to  the  left  auricle.  From  the  left  auricle  it  passes  into 
the  left  ventricle,  and  thence  into  the  aorta,  by  which  it  is  distributed  to 
the  capillaries  of  every  portion  of  the  body.  The  branches  of  the  aorta, 
from  being  distributed  to  the  general  system,  are  called  systemic  arteries; 
and  from  these  the  blood  passes  into  the  systemic  capillaries,  where  it 
again  becomes  dark  and  impure,  and  thence  into  the  branches  of  the 
systemic  veins,  which,  forming  by  their  union  two  large  trunks,  called 
the  superior  and  inferior  vena  cava,  discharge  their  contents  into  the  right 
auricle,  whence  we  supposed  the  blood  to  start. 

The  Valves  of  the  Heart. — The  valve  between  the  right  auricle 
and  ventricle  is  named  tricuspid  (5,  Fig.  99),  because  it  presents  three 
principal  cusps  or  subdivisions,  and  that  between  the  left  auricle  and  yen- 


FiG.  97. — Diagram  of  the  circulation  through  the  heart.  (Dalton.) 

tricle  bicuspid  for  mitral),  because  it  has  tiuo  such  portions  (6,  Fig.  93). 
But  in  both  valves  there  is  between  each  two  principal  portions  a  smaller 
one;  so  that  more  properly,  the  tricuspid  may  be  described  as  consisting 
of  six,  and  tlie  mitral  of  four,  portions.  Each  portion  is  of  triangular 
form,  its  apex  and  sides  lying  free  in  the  cavity  of  the  ventricle,  and  its 
base,  which  is  continuous  with  the  bases  of  the  neighboring  portions,  so 
as  to  form  an  annular  membrane  around  the  auriculo -ventricular  open- 
ing, being  fixed  to  a  tendinous  ring  which  encircles  the  orifice  between 
the  auricle  and  ventricle  and  receives  the  insertions  of  the  muscular  fibres 
of  both.  In  each  principal  cusp  may  be  distinguished  a  middle-piece, 
extending  from  its  base  to  its  apex,  and  including  about  half  its  width, 
which  is  thicker,  and  much  tougher  and  tighter  than  the  border-pieces 
or  edges. 

While  the  bases  of  the  several  portions  of  the  valves  are  fixed  to  the 


110 


HAND-BOOK  OF  PHYSIOLOGY. 


tendinous  rings,  their  yentricular  surfaces  and  borders  are  fastened  by- 
slender  tendinous  fibres,  the  chorclce  tendinece,  to  the  walls  of  the  ventri- 
cles, the  muscular  fibres  of  which  project  into  the  ventricular  cavity  in 
the  form  of  bundles  or  columns — the  cohimncB  carnece.  These  columns 
are  not  all  of  them  alike,  for  while  some  of  them  are  attached  along  their 
whole  length  on  one  side  and  by  their  extremities,  others  are  attached 
only  by  their  extremities;  and  a  third  set,  to  which  the  name  musculi 
2)cipiUares  has  been  given,  are  attached  to  the  wall  of  the  ventricle  by 
one  extremity  only,  the  other  projecting,  papilla-like,  into  the  cavity  of 
the  ventricle  (5,  Fig.  93),  and  having  attached  to  it  cliordce  tendinece. 
Of  the  tendinous  cords,  besides  those  which  pass  from  the  walls  of  the 
ventricle  and  the  musculi  papillares  to  the  margins  of  the  valves,  there 
are  some  of  especial  strength,  which  pass  from  the  same  parts  to  the  edges 
of  the  middle  and  thicker  portions  of  the  cusps  before  referred  to.  The 
ends  of  these  cords  are  spread  out  in  the  substance  of  the  valve,  giving 
its  middle  piece  its  peculiar  strength  and  toughness;  and  from  the  sides 
numerous  other  more  slender  and  branching  cords  are  given  off,  which 
are  attached  all  over  the  ventricular  surface  of  the  adjacent  border-pieces 
of  the  principal  portions  of  the  valves,  as  well  as  to  those  smaller  portions 
which  have  been  mentioned  as  lying  between  each  two  principal  ones. 
Moreover,  the  musculi  papillares  are  so  placed  that,  from  the  summit  of 
each,  tendinous  cords  i:)roceed  to  the  adjacent  halves  of  two  of  the  prin- 
cipal divisions,  and  to  one  intermediate  or  smaller  division,  of  the  valve. 

The  preceding  description  applies  equally  to  the  mitral  and  tricuspid 
valve;  but  it  should  be  added  that  the  mitral  is  considerably  thicker  and 
stronger  than  the  tricuspid,  in  accordance  with  the  greater  force  which 
it  is  called  upon  to  resist. 

It  has  been  already  said  that  while  the  ventricles  communicate,  on  the 
one  hand,  with  the  auricles,  they  communicate,  on  the  other,  with  the 
large  arteries  wliich  convey  the  blood  away  from  the  heart;  the  riglit  ven- 
tricle with  the  pulmonary  artery  (G,  Fig.  93),  which  conveys  blood  to  the 
lungs,  and  the  left  ventricle  with  the  aorta,  which  distributes  it  to  the 
general  system  (T,  Fig.  93).  And  as  the  auriculo-ventricular  orifice  is 
guarded  by  valves,  so  are  also  the  mouths  of  the  pulmonary  artery,  and 
aorta  (Figs.  9:3,  99). 

The  semilunar  valves,  three  in  number,  guard  the  orifice  of  each  of 
these  two  arteries.  They  are  nearly  alike  on  both  sides  of  the  heart;  but 
those  of  the  aorta  are  altogether  thicker  and  more  strongly  constructed 
than  tliose  of  tlie  pulmonary  artery,  in  accordance  witli  the  greater  pros- 
sure  which  tliey  liave  to  witlistand.  Each  valve  is  of  semilunar  shape,  its 
convex  margin  being  attached  to  a  fibrous  ring  at  tlio  place  of  junction 
of  the  artery  to  the  ventricle,  and  tlie  concave  or  nearly  straight  border 
l)eing  free,  so  that  eacli  valve  forms  a  little  pouch  like  a  watch-pocket 
(7,  l^^ig.  93).    Ill  the  centre  of  the  free  edge  of  tlie  valve,  which  contnius 


CIRCULATION  OF  THE  BLOOD. 


Ill 


a  fine  cord  of  fibrous  tissue,  is  a  small  fibrous  nodule,  the  coiyus  Arantii, 
and  from  this  and  from  the  attached  border  fine  fibres  extend  into  every 
part  of  the  mid  substance  of  the  valve,  except  a  small  lunated  space  just 
within  the  free  edge,  on  each  side  of  the  corpus  Arantii.  Here  the  valve 
is  thinnest,  and  composed  of  little  more  than  the  endocardium.  Thus 
constructed  and  attached,  the  three  semilunar  valves  are  placed  side  by 
side  around  the  arterial  orifice  of  each  ventricle,  so  as  to  form  three  little 
pouches,  which  can  be  separated  by  the  blood  passing  out  of  the  ventricle, 
but  which  immediately  afterward  are  pressed  together  so  as  to  prevent 
any  return  (7,  Fig.  93,  and  7,  Fig.  99).  This  will  be  again  referred  to. 
Opposite  each  of  the  semilunar  cusps,  both  in  the  aorta  and  pulmonary 
artery,  there  is  a  bulging  outward  of  the  wall  of  the  vessel:  these  bulg- 
ings  are  called  the  sinuses  of  Valsalva. 

Structure  of  the  Valves. — The  valves  of  the  heart  are  formed  es- 
sentially of  thick  layers  of  closely  woven  connective  and  elastic  tissue,  over 
which,  on  every  part,  is  reflected  the  endocardium. 

The  Actiok  of  the  Heakt. 

The  heart's  action  in  propelling  the  blood  consists  in  the  successive 
alternate  contraction  (systole)  and  relaxation  (diastole)  of  the  muscular 
walls  of  its  two  auricles  and  two  ventricles. 

Action  of  the  Auricles. — The  description  of  the  action  of  the  heart 
may  best  be  commenced  at  that  period  in  each  action  which  immedi- 
ately precedes  the  beat  of  the  heart  against  the  side  of  the  chest.  For  at 
this  time  the  whole  heart  is  in  a  passive  state,  the  walls  of  both  auricles 
and  ventricles  are  relaxed,  and  their  cavities  are  being  dilated.  The  auri- 
cles are  gradually  filling  with  blood  flowing  into  them  from  the  veins;  and 
a  portion  of  this  blood  passes  at  once  through  them  into  the  ventricles, 
the  opening  between  the  cavity  of  each  auricle  and  that  of  its  correspond- 
ing ventricle  being,  during  all  the  pause,  free  and  patent.  The  auricles, 
however,  receiving  more  blood  than  at  once  passes  through  them  to  the 
ventricles,  become,  near  the  end  of  the  pause,  fully  distended;  and  at  the 
end  of  the  pause,  they  contract  and  expel  their  contents  into  the  ventricles. 

The  contraction  of  the  auricles  is  sudden  and  very  quick;  it  commences 
at  the  entrance  of  the  great  veins  into  them,  and  is  thence  propagated 
toward  the  auriculo-ventricular  opening;  but  the  last  part  which  contracts 
is  the  auricular  appendix.  The  effect  of  this  contraction  of  the  auricles  is 
to  quicken  the  flow  of  blood  from  them  into  the  ventricles;  the  force  of 
their  contraction  not  being  sufficient  under  ordinary  circumstances  to 
cause  any  back-flow  into  the  veins.  The  reflux  of  blood  into  the  great 
veins  is,  moreover,  resisted  not  only  by  the  mass  of  blood  in  the  veins  and 
the  force  with  which  it  streams  into  the  auricles,  but  also  by  the  simulta- 
neous contraction  of  the  muscular  coats  with  which  the  large  veins  are 


112 


HAND-BOOK  OF  PHYSIOLOGY. 


provided  near  their  entrance  into  the  auricles.  Any  slight  regurgitation 
from  the  right  auricle  is  limited  also  by  the  valves  at  the  junction  of  the 
subclavian  and  internal  jugular  veins^  beyond  which  the  blood  cannot 
move  backward;  and  the  coronary  vein  is  preserved  from  it  by  a  valve  at 
its  mouth. 

in  birds  and  reptiles  regurgitation  from  the  right  auricle  is  prevented 
by  valves  placed  at  the  entrance  of  the  great  veins. 

During  the  auricular  contraction  the  force  of  the  blood  propelled 
into  the  ventricle  is  transmitted  in  all  directions,  but  being  insufficient 
to  separate  the  semilunar  valves,  it  is  expended  in  distending  the  ven- 
tricle, and,  by  a  reflux  of  the  current,  in  raising  and  gradually  closing  the 
auriculo-ventricular  valves,  which,  when  the  ventricle  is  full,  form  a  com- 
plete septum  between  it  and  the  auricle. 

Action  of  the  Ventricles. — The  blood  which  is  thus  driven,  by  the 
contraction  of  the  auricles,  into  the  corresponding  ventricles,  being  added 
to  that  which  had  already  flowed  into  them  during  the  heart's  pause,  is 
sufficient  to  complete  their  diastole.  Thus  distended,  they  immediately 
contract:  so  immediately,  indeed,  that  their  systole  looks  as  if  it  were 
continuous  with  that  of  the  auricles.  The  ventricles  contract  much  more 
slowly  than  the  auricles,  and  in  their  contraction  probably  always 
thoroughly  empty  themselves,  differing  in  this  respect  from  the  auricles, 
in  which,  even  after  their  complete  contraction,  a  small  quantity  of  blood 
remains.  The  shape  of  both  ventricles  during  systole  undergoes  an  alter- 
ation, the  left  probably  not  altering  in  length  but  to  a  certain  degree  in 
breadth,  the  diameters  in  the  plane  of  the  base  being  diminished.  The 
right  ventricle  does  actually  shorten  to  a  small  extent.  The  systole  has 
the  effect  of  diminishing  the  diameter  of  the  base,  especially  in  the  plane 
of  the  auriculo-ventricular  valves;  but  the  length  of  the  heart  as  a  whole 
is  not  altered.  (Ludwig.)  During  the  systole  of  the  ventricles,  too,  the 
aorta  and  pulmonary  artery,  being  filled  with  blood  by  the  force  of  the 
ventricular  action  against  considerable  resistance,  elongate  as  well  as  ex- 
pand, and  the  whole  heart  moves  slightly  toAvard  the  right  and  forward, 
twisting  on  its  long  axis,  and  exposing  more  of  the  left  ventricle  ante- 
riorly than  is  usually  in  front.  When  the  systole  ends  tlie  heart  resumes 
its  former  position,  rotating  to  the  left  again  as  the  aorta  and  pulmonary 
artery  contract. 

Functions  of  the  Auriculo-Ventricular  Valves. — The  disten- 
sion of  the  ventricles  with  blood  continues  throughout  the  wliole  period 
of  tlieir  diastole.  Tlie  auriculo-ventricular  valves  are  gradually  brought 
into  play  by  soine  of  the  blood  getting  behind  the  cusps  and  floating  them 
u});  and  ])y  the  time  that  the  diastole  is  complete,  the  valves  are  no  doubt 
in  apposition,  the  completion  of  this  being  brought  about  by  the  reflex 
current  caused  by  the  systole  of  the  auricles.     This  elevation  of  the  au- 


CIRCULATION  OF  THE  BLOOD. 


113 


riculo-ventricular  valves  is,  no  doubt,  materially  aided  by  the  action  of  the 
elastic  tissue  which  has  been  shown  to  exist  so  largely  in  their  structure, 
especially  on  the  auricular  surface.  At  any  rate  at  the  commencement 
of  the  ventricular  systole  they  are  completely  closed.  It  should  be  recol- 
lected that  the  diminution  in  the  breadth  of  the  base  of  the  heart  in  its 
transverse  diameters  during  ventricular  systole  is  especially  marked  in  the 
neighborhood  of  the  auriculo- ventricular  rings,  and  thus  aids  in  render- 
ing the  auriculo-ventricular  valves  competent  to  close  the  openings,  by 
greatly  diminishing  their  diameter.  The  margins  of  the  cusps  of  the 
valves  are  still  more  secured  in  apposition  with  another,  by  the  simulta- 
neous contraction  of  the  musculi  papillares,  whose  chordae  tendineae  have  a 
special  mode  of  attachment  for  this  object  (p.  110).  As  in  the  case  of 
the  semilunar  valves  to  be  immediately  described,  the  auriculo-ventricular 
valves  meet  not  by  their  edges  only,  but  by  the  opposed  surfaces  of  their 
thin  outer  borders.  The  semilunar  valves,  on  the  other  hand,  which  are 
closed  in  the  intervals  of  the  ventricle's  contraction  (Fig.  92,  6),  are 
forced  apart  by  the  same  pressure  that  tightens  the  auriculo-ventricular 
valves;  and,  thus,  the  whole  force  of  the  contracting  ventricles  is  directed 
to  the  expulsion  of  blood  through  the  aorta  and  pulmonary  artery. 

The  form  and  position  of  the  fleshy  columns  on  the  internal  walls  of 
the  ventricle  no  doubt  help  to  produce  this  obliteration  of  the  cavity  dur- 
ing their  contraction;  and  the  completeness  of  the  closure  may  often  be 
observed  on  making  a  transverse  section  of  a  heart  shortly  after  death,  in 
any  case  in  which  the  contraction  of  the  rigor  mortis  is  very  marked  (Fig. 
94).  In  such  a  case  only  a  central  fissure  may  be  discernible  to  the  eye 
in  the  place  of  the  cavity  of  each  ventricle. 

If  there  were  only  circular  fibres  forming  the  ventricular  wall,  it  is 
evident  that  on  systole  the  ventricle  would  elongate;  if  there  were 
only  longitudinal  fibres  the  ventricle  would  shorten  on  systole;  but  there 
are  both.  The  tendency  to  alter  in  length  is  thus  counterbalanced,  and 
the  whole  force  of  the  contraction  is  expended  in  diminishing  the  cavity 
of  the  ventricle;  or,  in  other  words,  in  expelling  its  contents. 

On  the  conclusion  of  the  systole  the  ventricular  walls  tend  to  expand 
by  virtue  of  their  elasticity,  and  a  negative  pressure  is  set  up,  which  tends 
to  suck  in  the  blood.  This  negative  or  suctional  pressure  on  the  left  side 
of  the  heart  is  of  the  highest  importance  in  helping  the  pulmonary  cir- 
culation. It  has  been  found  to  be  equal  to  23  mm.  of  mercury,  and  is. 
quite  independent  of  the  aspiration  or  suction  power  of  the  thorax  in  aid-^ 
ing  the  blood-flow  to  the  heart,  to  be  described  in  the  chapter  on  Eesj)ira- 
tion. 

Function  of  the  Musculi  Papillares. — The  special  function  of 
the  musculi  2^apiUares  is  to  prevent  the  auriculo-ventricular  valves  from 
being  everted  into  the  auricle.    For  the  chordse  tendineee  might  allow 
the  valves  to  be  pressed  back  into  the  auricle,  were  it  not  that  when  the 
Vol.  I.— 8. 


114 


HA™-B00K  of  PHYSIOLOaY. 


wall  of  the  ventricle  is  brought  by  its  contraction  nearer  the  auriculo- 
ventricular  orifice,  the  musculi  papillares  more  than  compensate  for  this 
by  their  own  contraction' — holding  the  cords  tight,  and,  by  pulling  down 
the  valves,  adding  slightly  to  the  force  with  which  the  blood  is  expelled. 

What  has  been  said  applies  equally  to  the  auriculo-ventricular  valves 
on  both  sides  of  the  heart,  and  of  both  alike  the  closure  is  generally  com- 
plete every  time  the  ventricles  contract.  But  in  some  circumstances  the 
closure  of  the  tricuspid  valve  is  not  complete,  and  a  certain  quantity  of 
blood  is  forced  back  into  the  auricle.  This  has  been  called  the  safety- 
valve  action  of  this  valve.  The  circumstances  in  which  it  usually  hapjDcns 
are  those  in  which  the  vessels  of  the  lung  are  already  full  enough  when 
the  right  ventricle  contracts,  as  e.g.,  in  certain  pulmonary  diseases,  in 
ver}  active  exertion,  and  in  great  efforts.  In  these  cases,  the  tricuspid 
vah  e  does  not  completely  close,  and  the  regurgitation  of  the  blood  may 
be  indicated  by  a  pulsation  in  the  jugular  veins  synchronous  with  that  in 
the  carotid  arteries. 

Function  of  the  Semilunar  Valves. — The  arterial  or  semilunar 
valves  are  forced  apart  by  the  out-streaming  blood,  with  which  the  con- 
tracting ventricle  dilates  the  large  arteries.  The  dilation  of  the  arteries 
is,  in  a  peculiar  manner,  adapted  to  bring  the  valves  into  action.  The 
lower  borders  of  the  semilunar  valves  are  attached  to  the  inner  surface  of 
a  tendinous  ring,  which  is,  as  it  were,  inlaid  at  the  orifice  of  the  artery, 
between  the  muscular  fibres  of  the  ventricle  and  the  elastic  fibres  of  the  walls 
of  the  artery.  The  tissue  of  this  ring  is  tough,  and  does  not  admit  of 
extension  under  such  pressure  as  it  is  commonly  exposed  to;  the  valves 
are  equally  inextensile,  being,  as  already  mentioned,  formed  of  tough,  close- 
textured,  fibrous  tissue,  with  strong  interwoven  cords,  and  covered  with 
endocardium.  Hence,  when  the  ventricle  propels  blood  through  the  ori- 
fice and  into  the  canal  of  the  artery,  the  lateral  pressure  which  it  exercises 
is  sufficient  to  dilate  the  walls  of  the  artery,  but  not  enough  to  stretch  in  an 
equal  degree,  if  at  all,  the  unyielding  valves  and  the  ring  to  which  their 
lower  borders  are  attached.  The  effect,  therefore,  of  each  such  propul- 
sion of  blood  from  the  ventricle  is,  that  the  wall  of  the  first  portion  of 
the  artery  is  dilated  into  three  pouches  behind  the  valves,  while  the  free 
margins  of  the  valves  are  draAvn  inward  toward  its  centre  (Fig.  98,  b). 
Their  j)ositions  may  be  explained  by  the  diagrams,  in  which  the  continu- 
ous lines  represent  a  transverse  section  of  tlie  arterial  walls,  the  dotted 
ones  the  edges  of  the  valves,  firstly,  when  the  valves  are  nearest  to  the 
walls  (a),  and,  secondly,  when,  tlie  walls  being  dilated,  the  valves  are 
drawn  away  from  them  (b). 

Tliis  ])osition  of  tlu^  valves  and  arterial  walls  is  retained  so  long  as  the 
ventricle  (toiitiuues  in  contraction:  but,  as  soon  as  it  relaxes,  and  the  di- 
liiicd  jiiicrial  walls  can  recoil  by  tlieir  ehisticity,  the  blood  is  forced  back- 
ward lownrd  the  ventricles  as  onward  in  the  course  of  the  circnlation. 


CIRCULATION  OF  THE  BLOOD. 


115 


Part  of  the  blood  thus  forced  back  lies  in  the  pouches  (sinuses  of  Valsalva) 
(a,  Fig.  98,  b)  between  the  valves  and  the  arterial  walls;  and  the  valves 
are  by  it  pressed  together  till  their  thin  lunated  margins  meet  in  three 


Fig.  98.— Sections  of  aorta,  to  show  the  action  of  the  semilunar  valves,  a  is  intended  to  show 
the  valves,  represented  by  the  dotted  lines,  pressed  toward  the  arterial  walls,  represented  by  the  con- 
tinuous outer  line,  b  (after  Hunter)  shows  the  arterial  wall  distended  into  three  pouches  ( a ),  and 
drawn  away  from  the  valves,  which  are  straightened  into  the  form  of  an  equilateral  triangle,  as  rep- 
resented by  the  dotted  hues. 

« 

lines  radiating  from  the  centre  to  the  circumference  of  the  artery  (7  and 
8,  Fig.  99). 

The  contact  of  the  valves  in  this  position,  and  the  complete  closure  of 
the  arterial  orifice,  are  secured  by  the  peculiar  construction  of  their  bor- 
ders before  mentioned.    Among  the  cords  which  are  interwoven  in  the 


Fig.  99.  — View  of  the  base  of  the  ventricular  part  of  the  heart,  showing  the  relative  position  of 
the  arterial  and  auriculo-ventricular  orifices. — %.  The  muscular  fibres  of  the  ventricles  are  exposed 
by  the  removal  of  the  pericardium,  fat,  blood-vessels,  etc. ;  the  pulmonary  artery  and  aorta  have  been 
removed  by  a  section  made  immediately  beyond  the  attachment  of  the  semilunar  valves,  and  the  au- 
ricles have  been  removed  immediately" above  the  auriculo-ventricular  orifices.  The  semilunar  and 
auriculo-ventricular  valves  are  in  the  nearly  closed  condition.  1,  1,  the  base  of  the  right  ventricle; 
1',  the  conus  arteriosus;  2,  2,  the  base  of  the  left  ventricle;  3,  3,  the  divided  wall  of  the  right  auricle; 
4,  that  of  the  left;  5,  5,'  5",  the  tricuspid  valve;  6,  6',  the  mitral  valve.  In  the  angles  between  these 
segments  are  seen  the  smaller  fringes  frequently  observed;  7,  the  anterior  part  of  the  pulmonary  ar- 
tery ;  8,  placed  upon  the  posterior  part  of  the  root  of  the  aorta ;  9,  the  right,  9',  the  left  coronary  artery. 
(Allen  Thomson.) 


substance  of  the  valves,  are  two  of  greater  strength  and  prominence  than 
the  rest;  of  which  one  extends  along  the  free  border  of  each  valve,  and 
the  other  forms  a  double  curve  or  festoon  just  below  the  free  border. 


116 


HAND-BOOK  OF  PHYSIOLOGY. 


Each  of  these  cords  is  attached  by  its  outer  extremities  to  the  outer  end 
of  the  free  margin  of  its  valve,  and  in  the  middle  to  the  corpus  Arantii; 
they  thus  enclose  a  lunated  space  from  a  line  to  a  line  and  a  half  in  width, 
in  which  space  the  substance  of  the  valve  is  much  thinner  and  more  pliant 
than  elsewhere.  When  the  valves  are  pressed  down,  all  these  parts  or 
spaces  of  their  surfaces  come  into  contact,  and  the  closure  of  the  arterial 
orifice  is  thus  secured  by  the  apposition  not  of  the  mere  edges  of  the 
valves,  but  of  all  those  thin  lunated  parts  of  each  which  lie  between  the 
free  edges  and  the  cords  next  below  them.  These  parts  are  firmly  pressed 
together,  and  the  greater  the  pressure  that  falls  on  them  the  closer  and 
".nore  secure  is  their  apposition.  The  corpora  Arantii  meet  at  the  centre 
of  the  arterial  orifice  when  the  valves  are  down,  and  they  probably  assist 
in  the  closure;  but  they  are  not  essential  to  it,  for,  not  unfrequently, 
they  are  wanting  in  the  valves  of  the  pulmonary  artery,  which  are  then 
extended  in  larger,  thin,  flapping  margins.  In 
valves  of  this  form,  also,  the  inlaid  cords  are  less 
distinct  than  in  those  with  corpora  Arantii;  yet  the 
closure  by  contact  of  their  surfaces  is  not  less 
secure. 

It  has  been  clearly  shown  that  this  pressure  of  the 
blood  is  not  entirely  sustained  by  the  valves  alone,  but 
in  part  by  the  muscular  substance  of  the  ventricle 
(Savory).  By  making  vertical  sections  (Fig.  100) 
through  various  parts  of  the  tendinous  rings  it  is  pos- 
sible to  show  clearly  that  the  aorta  and  pulmonary 
artery,  expanding  toward  their  termination,  are  sit- 
uated upon  the  Older  edge  of  the  thick  upper  border 
of  the  ventricles,  and  that  consequently  the  portion 
of  each  semilunar  valve  adjacent  to  the  vessel  passes 
over  and  rests  upon  the  muscular  substance — being 
thus  supported,  as  it  were,  on  a  kind  of  muscular  floor 
formed  by  the  upper  border  of  the  ventricle.  The  result  of  this  arrange- 
ment is  that  the  reflux  of  the  blood  is  most  efficiently  sustained  by  the 
ventricular  wall.  *  » 

As  soon  as  the  auricles  have  completed  their  contraction  they  begin 
again  to  dilate,  and  to  be  refilled  with  blood,  which  fiows  into  them  in  a 
steady  stream  tlirougli  tlie  great  venous  trunks.  They  are  thus  filling- 
during  all  the  time  in  which  the  ventricles  are  contracting;  and  the  con- 
traction of  tlie  ventricles  being  ended,  these  also  again  dilate,  and  receive 
again  tlie  l)lood  that  flows  into  them  from  the  auricles.  By  the  time  thtit 
tlie  ventricles  are  thus  from  one-third  to  two-thirds  full,  the  auricles  are 

'  Savory's  prciuirations,  illustralin^;  this  and  oIIut  points  in  relation  to  the  struc- 
ture and  functions  of  the  valves  of  the  heart,  are  in  the  Museum  of  St.  Bartholomew's 
Hospital. 


Fig.  100.— Vertical  sec- 
tion tlrroug;h  the  aorta 
at  its  junction  with  the 
left  ventricle,  a.  Section 
of  aorta,  bb.  Section  of 
two  valves.  c\  Section  of 
wall  of  ventricle,  c?.  In- 
ternal surface  of  ven- 
tricle. 


CIRCULATION  OF  THE  BLOOD 


117 


distended;  these,  then  suddenly  contracting,  fill  up  the  ventricles,  as 
already  described  (p.  111). 

Cardiac  Revolution. — If  we  suppose  a  cardiac  revolution  divided 

into  five  parts,  one  of  these  will  be  occupied  by  the  contraction  of  the 
auricles,  two  by  that  of  the  ventricles,  and  two  by  repose  of  both  auricles 
and  ventricles. 

Contraction  of  Auricles  .    .    .    1  -|-  Eepose  of  Auricles    .    .    .  4=5 
"  Ventricles    .    .    %  -\-      "         Ventricles     .    .  3=5 

Eepose  (no  contraction  of  either 

auricles  or  ventricles)  .    .    .    2  +  Contraction  (of  either  auri- 

—         cles  or  ventricles)  .    .    .  3=5 
5 

If  the  speed  of  the  heart  be  quickened,  the  time  occupied  by  each 
cardiac  revolution  is  of  course  diminished,  but  the  diminution  a"ffects  only 
the  diastole  and  pause.  The  systole  of  the  ventricles  occupies  very  much 
the  same  time,  about  -5%-  sec,  whatever  the  pulse-rate. 

The  periods  in  which  the  several  valves  of  the  heart  are  in  action  may 
be  connected  with  the  foregoing  table;  for  the  auriculo-ventricular  valves 
are  closed,  and  the  arterial  valves  are  open  during  the  whole  time  of  the 
ventricular  contraction,  while,  during  the  dilation  and  distension  of  the 
ventricles  the  latter  valves  are  shut,  the  former  open.  Thus  whenever 
the  auriculo-ventricular  valves  are  open,  the  arterial  valves  are  closed  and 
vice  versa. 

SOUN-DS  OF  THE  HeAKT. 

When  the  ear  is  placed  over  the  region  of  the  heart,  two  sounds  may 
be  heard  at  every  beat  of  the  heart,  which  follow  in  quick  succession, 
and  are  succeeded  by  pause  or  period  of  silence.  first  sound  is  dull 
and  prolonged;  its  commencement  coincides  with  the  impulse  of  the 
heart,  and  just  precedes  the  pulse  at  the  wrist.  The  second  is  a  shorter 
and  sharper  sound,  with  a  somewhat  flapping  character,  and  follows  close 
after  the  arterial  pulse.  The  period  of  time  occupied  respectively  by  the 
two  sounds  taken  together,  and  by  the  pause,  are  almost  exactly  equal. 
The  relative  length  of  time  occupied  by  each  sound,  as  compared  with 
the  other,  is  a  little  uncertain.  The  difference  may  be  best  appreci- 
ated by  considering  the  different  forces  concerned  in  the  production  of 
the  two  sounds.  In  one  case  there  is  a  strong,  comparatively  slow,  con- 
traction of  a  large  mass  of  muscular  fibres,  urging  forward  a  certain 
quantity  of  fluid  against  considerable  resistance;  while  in  the  other  it  is  a 
strong  but  shorter  and  sharper  recoil  of  the  elastic  coat  of  the  large 
arteries, — shorter  because  there  is  no  resistance  to  the  flapping  back  of 


118 


HAND-BOOK  OF  PHYSIOLOGY. 


the  semilunar  valves,  as  there  was  to  their  opening.  The  sounds  may 
be  expressed  by  saying  the  words  luhh — dup  (0.  J.  B.  Williams). 

The  events  which  correspond,  in  point  of  time,  with  the  first  sound, 
are  (1)  the  contraction  of  the  ventricles,  (2)  the  first  part  of  the  dilatation 
of  the  auricles,  (3)  the  closure  of  the  auriculo-ventricular  valves,  (4)  the 
opening  of  the  semilunar  valves,  and  (5)  the  propulsion  of  blood  into  the 
arteries.  The  sound  is  succeeded,  in  about  one-thirtieth  of  a  second,  by 
the  pulsation  of  the  facial  arteries,  and  in  about  one-sixth  of  a  second, 
by  the  pulsation  of  the  arteries  at  the  wrist.  The  second  sound,  in  point 
of  time,  immediately  follows  the  cessation  of  the  ventricular  contraction, 
and  corresponds  with  [a)  the  closure  of  the  semilunar  valves,  {h)  the  con- 
tinued dilatation  of  the  auricles,  (c)  the  commencing  dilatation  of  the 
ventricles,  and  {d)  the  opening  of  the  auriculo-ventricular  valves.  The 
pause  immediately  follows  the  second  sound,  and  corresponds  m  its  first 
part  with  the  completed  distension  of  the  auricles,  and  in  its  seco7id 
with  their  contraction,  and  the  completed  distension  of  the  ventricles; 
the  auriculo-ventricular  valves  being,  all  the  time  of  the  pause,  open,  and 
the  arterial  valves  closed. 

Causes. — The  chief  cause  of  the  first  sound  of  the  heart  appears  to 
be  the  vibration  of  the  auriculo-ventricular  valves,  due  to  their  stretch- 
ing, and  also,  but  to  a  less  extent,  of  the  ventricular  walls,  and  coats  of 
the  aorta  and  pulmonary  artery,  all  of  which  parts  are  suddenly  put  into 
a  state  of  tension  at  the  moment  of  ventricular  contraction.  The  effect 
may  be  intensified  by  the  muscular  soiond  produced  by  contraction  of  the 
mass  of  muscular  fibres  which  form  the  ventricle. 

The  cause  of  the  second  sound  is  more  simple  than  that  of  the  first. 
It  is  probably  due  entirely  to  the  sudden  closure  and  consequent  vihration 
of  the  semilunar  valves  when  they  are  pressed  down  across  the  orifices  of 
the  aorta  and  pulmonary  artery.  The  influence  of  the  valves  in  produc- 
ing the  sound  is  illustrated  by  the  experiment  performed  on  large  ani- 
mals, such  as  calves,  in  which  the  results  could  be  fully  appreciated.  In 
these  experiments  two  delicate  curved  needles  were  inserted,  one  into  the 
aorta,  and  another  into  tlie  pulmonary  artery,  below  the  line  of  attach- 
ment of  the  semilunar  valves,  and,  after  being  carried  upward  aboitt  half 
an  inch,  were  brought  out  again  through  the  coats  of  the  respective  vessels, 
so  that  in  each  vessel  one  valve  was  included  between  the  arterial  walls 
and  the  wire.  Upon  applying  the  stethoscope  to  the  vessels,  after  such 
an  operation,  tlie  second  sound  had  ceased  to  be  audible.  Disease  of 
tliesc  valves,  wlien  so  extensive  as  to  interfere  with  their  efficient  action, 
also  often  demonstrates  tlie  same  fact  by  modifying  or  destroying  the 
distinctness  of  tlic  secoiul  sound. 

One  reason  for  tlu^  second  sound  being  a  clearer  and  sliar})er  one  than 
the  first  m;iy  be,  tliat  the  semihniar  valves  are  not  covered  in  by  the  thick 
layer  of  fibres  ('()iiij)()siiig        wi.lls  of  (lie  to  such  an  extent  as  are 


CIRCULATION  OF  THE  BLOOD.  119 

the  aitriculo-ventricular.  It  might  be  expected  therefore  thiit  their  vibra- 
tion would  be  more  easily  heard  through  a  stethoscope  applied  to  the 
walls  of  the  chest. 

The  contraction  of  the  auricles  which  takes  place  in  the  eiid  of  the 
pause  is  inaudible  outside  the  chest,  but  may  be  heard,  when  the  heart 
is  exposed  and  the  stethoscope  placed  on  it,  as  a  slight  sound  preceding 
and  continued  into  the  louder  sound  of  the  ventricular  contraction. 

The  Impulse  of  the  Heart. — At  the  commencement  of  each  ven- 
tricular contraction,  the  heart  may  be  felt  to  beat  with  a  slight  shock  or 
impulse  against  the  walls  of  the  chest.  The  force  of  the  impulse,  and  the 
extent  to  which  it  may  be  perceived  beyond  this  point,  vary  considerably 
in  different  individuals,  and  in  the  same  individual  under  different  cir- 
cumstances. It  is  felt  more  distinctly,  and  over  a  larger  extent  of  surface, 
in  emaciated  than  in  fat  and  robust  persons,  and  more  during  a  forced  ex- 
piration than  in  a  deep  inspiration;  for,  in  the  one  case,  the  intervention 
of  a  thick  layer  of  fat  or  muscle  between  the  heart  and  the  surface  of  the 
chest,  and  in  the  other  the  inflation  of  the  portion  of  lung  which  overlaps 
the  heart,  prevents  the  impulse  from  being  fully  transmitted  to  the  sur- 
face. An  excited  action  of  the  heart,  and  especially  a  hypertrophied  con- 
dition of  the  ventricles,  will  increase  the  impulse;  while  a  depressed  con- 
dition, or  an  atrophied  state  of  the  ventricular  walls,  will  diminish  it. 

Cause  of  the  Impulse. — During  the  period  which  precedes  the 
ventricular  systole,  the  apex  of  the  heart  is  situated  upon  the  diaphragm 
and  against  the  chest-wall  in  the  fifth  intercostal  space.  When  the  ven- 
tricles contract,  their  walls  become  hard  and  tense,  since  to  expel  their 
contents  into  the  arteries  is  a  distinctly  laborious  action,  as  it  is  resisted 
by  the  tension  within  the  vessels.  It  is  to  this  sudden  hardening  that  the 
impulse  of  the  heart  against  the  chest- wall  is  due,  and  the  shock  of  the 
sudden  tension  may  be  felt  not  only  externally,  but  also  internally,  if  the 
abdomen  of  an  animal  be  opened  and  the  fiuger  be  placed  upon  the  under 
surface  of  the  diaphragm,  at  a  point  corresponding  to  the  under  surface 
of  the  ventricle.  The  shock  is  felt,  and  possibly  seen  more  distinctly, 
because  of  the  partial  rotation  of  the  heart,  already  spoken  of,  along  its 
long  axis  toward  the  right.  The  movement  produced  by  the  ventricular 
contraction  may  be  registered  by  means  of  an  instrument  called  the  cardio- 
graph, and  it  -will  be  found  to  correspond  almost  exactly  with  a  tracing 
obtained  by  the  same  instrument  applied  over  the  contracting  ventricle 
itself. 

The  Cardiograph  (Fig.  101)  consists  of  a  cup-shaped  metal  box,  over 
the  open  front  of  which  is  stretched  an  elastic  membrane,  upon  which  is 
fixed  a  small  knob  of  hard  wood  or  ivory.  This  knob,  however,  may  be 
attached  instead,  as  in  the  figure,  to  the  side  of  the  box  by  means  of  a 
spring,  and  may  be  made  to  act  upon  a  metal  disc  attached  to  the  elastic 
mem.brane. 


120 


HAND-BOOK  OF  PHYSIOLOGY. 


The  knob  (a)  is  for  application  to  the  chest-wall  over  the  place  of  the 
greatest  impulse  of  the  heart.    The  box  or  tympanum  communicates  b}' 


means  of  an  air-tight  elastic  tube  (/)  with  the 
interior  of  a  second  tympanum  (Fig.  102,  h),  in 
connection  with  which  is  a  long  and  light  lever 
{a).  The  shock  of  the  heart's  impulse  being 
communicated  to  the  ivory  knob,  and  through 
it  to  the  first  tympanum,  the  effect  is,  of  course, 
at  once  transmitted  by  the  column  of  air  in 
the  elastic  tube  to  the  interior  of  the  second 
tympanum,  also  closed,  and  through  the  elastic 
and  movable  lid  of  the  latter  to  the  lever,  which 
is  placed  in  connection  with  a  registering  appa- 


FiG  101  ratus,  which  consists  generally  of  a  cylinder  or 

Cardiograph.   (Sanderson's.)  cOVercd  with    Smokcd   paper,  revolving 

according  to  a  definite  velocity  by  clockwork.    The  point  of  the  lever 
writes  upon  the  paper,  and  a  tracing  of  the  heart's  impulse  is  thus  obtained. 
By  placing  three  small  india-rubber  air  -bags  in  the  interior  resjjec- 


FiG.  102.— Marey's  Tambour  ( & ),  to  which  the  movement  of  the  column  of  air  in  the  first  tym- 
panmn  is  conducted  by  tlie  tube,  /,  and  from  -wliicli  it  is  communicated  by  the  lever,  a,  to  a  revolving 
cylinder,  so  that  tlie  tracing  of  the  movement  of  the  impulse  beat  is  obtained. 

tively  of  the  right  auricle,  the  right  ventricle,  and  in  an  intercostal  space 
in  front  of  the  heart  of  living  animals  (horse),  and  placing  these  bags,  by 
means  of  long  narrow  tubes,  in  communication  with  three  levers,  arranged 


Fig.  103.— Tracing  of  t\w  impulse  of  the  heart  of  man.  (IMaivy.) 

one  over  the  otlier  in  connection  with  a  registci-ing  :i])]):iralns  (Fig.  104), 
MM.  Chauveau  and  Marey  have  been  able  to  measure  willi  inucli  accuracy 
tlu^  variations  of  tlie  endocardial  pressure  and  tlu>  comparative  dnration 


OIKOULATlOxN^  OF  THE  BLOOD. 


121 


of  the  contractions  of  the  auricles  and  ventricles.  By  means  of  the  same 
apparatus,  the  synclironism  of  the  impulse  with  the  contraction  of  the 
ventricles,  is  also  well  shown;  and  the  causes  of  the  several  vibrations  of 
which  it  is  really  composed,  have  been  discovered. 

In  the  tracing  (Fig  105),  the  intervals  between  the  vertical  lines  rep- 
resent periods  of  a  tenth  of  a  second.    The  parts  on  which  any  given 


Fig.  104. — Apparatus  of  MM.  Chauveau  and  Marey  for  estimating  the  variations  of  endocardial 
pressure,  and  production  of  impulse  of  the  heart. 


vertical  line  falls  represent,  of  course,  simultaneous  events.  Thus, — it 
will  be  seen  that  the  contraction  of  the  auricle,  indicated  by  the  upheaval 
of  the  tracing  at  A  in  first  tracing,  causes  a  slight  increase  of  pressure  in 
the  ventricle  (a'  in  second  tracing),  and  produces  a  tiny  impulse  (a"  in 
third  tracing).  So  also,  the  closure  of  the 
semilunar  valves,  while  it  causes  a  momen- 
tarily increased  pressure  in  the  ventricle  at  d', 
does  not  fail  to  affect  the  pressure  in  the  auri- 
cle d",  and  to  leave  its  mark  in  the  tracing  of 
the  impulse  also,  d''. 

The  large  upheaval  of  the  ventricular  and 
the  impulse  tracings,  between  a'  and  d',  and 
a"  and  d",  are  caused  by  the  ventricular  con- 
traction, while  the  smaller  undulations,  between 
B  and  c,  b'  and  c',  b"  and  c",  are  caused  by 
the  vibrations  consequent  on  the  tightening 
and  closure  of  the  auriculo- ventricular  valves. 

Although,  no  doubt,  the  method  thus  de- 
scribed may  show  a  perfectly  correct  view  of 
the  endocardiac  pressure  variations,  it  should  be 
recollected  that  the  muscular  walls  may  grip  the  air-bags,  even  after  the 
complete  expulsion  of  the  contents  of  the  chamber,  and  so  the  lever  might 
remain  for  a  too  long  time  in  the  position  of  extreme  tension,  and  woi:^d 


Fig.  105.— Tracings  of  (1),  In- 
tra-auricular,  and  (2),  Intra- ven- 
tricular pressures,  and  (3),  of  the 
impulse  of  the  heart,  to  be  read 
from  left  to  right,  obtained  by 
Chauveau  and  Marey 's  apparatus. 


122 


HAND-BOOK  OF  PHYSIOLOGY 


represent  on  the  tracing  not  only,  as  it  ought  to  do,  the  auricular  or 
ventricular  pressure  on  the  blood,  but,  also  afterward,  the  muscular  pres- 
sure exerted  upon  the  bags  themselves.    (M.  Foster.) 


Fkequency  and  Force  of  the  Heart's  Action. 

The  heart  of  a  healthy  adult  man  contracts  from  seventy  to  seventy-five 
times  in  a  minute;  but  many  circumstances  cause  this  rate,  which  of 
course  corresponds  with  that  of  the  arterial  pulse,  to  vary  even  in  health. 
The  chief  are  age,  temperament,  sex,  food  and  drink,  exercise,  time  of 
day,  posture,  atmospheric  pressure,  temperature. 

Age. — The  frequency  of  the  heart's  action  gradually  diminishes  from 
the  commencement  to  near  the  end  of  life,  but  is  said  to  rise  again 
somewhat  in  extreme  old  age,  thus: — 

Before  birth  the  average  number  of  pulses  in  a  minute  is  150 

.  Just  after  birth   from  140  to  130 

During  the  first  year      ....  130  "  115 

During  the  second  year  .       .       .       .  "    115  100 

During  the  third  year     .       .       .       .  "    100  90 

About  the  seventh  year  .       .       .       .  "     90  85 
Abo  at  the  fourteenth  year,  the  average 

number  of  pulses  in  a  minute  is  85  80 

In  adult  age   80  70 

In  old  age      .       .       .       .       .       .  "     70  "  60 

In  decrepitude       .       .       .       .       .  "     75  65 

Temperament  and  Sex. — In  persons  of  sanguine  temperament,  the 
heart  acts  somewhat  more  frequently  than  in  those  of  the  phlegmatic; 
and  in  the  female  sex  more  frequently  than  in  the  male. 

Food  and  Drink.  Exercise. — After  a  meal  its  action  is  accelerated, 
and  still  more  so  during  bodily  exertion  or  mental  excitement;  it  is  slower 
during  sleep. 

Diurnal  Variation. — It  appears  that,  in  the  state  of  healtli,  the  pulse 
is  most  frequent  in  the  morning,  and  becomes  gradually  slower  as  the  day 
advances,  and  that  this  diminution  of  frequency  is  both  more  regular 
and  more  rapid  in  the  evening  than  in  the  morning. 

Posture. — It  is  found  that,  as  a  general  rule,  the  pulse,  especially  in 
the  adult  male,  is  more  frequent  in  the  standing  than  in  the  sitting  })os- 
turc,  and  in  the  latter  than  in  the  recuinbeiit  position;  the  difiorence 
being  greatest  between  the  standing  and  the  sitting  posture.  The  eifect 
of  (;liange  of  ])osture  is  greater  jis  the  frequency  of  tlio  pulse  is  greater, 
and,  acH'ordiiigly,  is  more  marked  in  the  morning  than  in  the  evening. 
By  snp])()rting  the  body  in  different  postures,  without  the  aid  of  mus- 
(;ulaT  effort  of  the  individual,  it  has  been  proved  that  the  increased  fre- 
(juency  of  the  pulse  in  the  sitting  and  standing  ])()sitions  is  dependent 
u])on  the  muscular  exertion  engaged  in  maintaining  tlunn;  the  usual 
effect  of  these  postures  on  the  ])ulse  being  almost  entirely  prevented  when 
the  usually  at  tcnchmt  muscular  exertion  was  rcMidered  unnecessary,  ((luy.) 


CIRCULATION  OF  THE  BLOOD. 


123 


Atmospheric  Presmre. — The  frequency  of  the  pulse  increases  in  a 
corresponding  ratio  with  the  elevation  above  the  sea. 

Temperature. — The  rapidity  and  force  of  the  heart's  contractions  are 
largely  influenced  by  variations  of  temperature.  The  frog's  heart,  when 
excised,  ceases  to  beat  if  the  temperature  be  reduced  to  32°  F.  (0°  C). 
When  heat  is  gradually  applied  to  it,  both  the  speed  and  force  of  the 
heart's  contractions  increase  till  they  reach  a  maximum.  If  the  tem- 
perature is  still  further  raised,  the  beats  become  irregular  and  feeble,  and 
the  heart  at  length  stands  still  in  a  condition  of  " heat -rigor. 

Similar  effects  are  produced  in  warm-blooded  animals.  In  the  rabbit, 
the  number  of  heart-beats  is  more  than  doubled  when  the  temperature  of 
the  air  was  maintained  at  105°  F.  (40°.5  C).  At  113°— 114°  F.  (45°  C), 
the  rabbit's  heart  ceases  to  beat. 

Relative  Frequency  of  the  Pulse  to  that  of  Respiration. — 

In  health  there  is  observed  a  nearly  uniform  relation  between  the  fre- 
quency of  the  pulse  and  of  the  respirations;  the  proportion  being,  on  an 
average,  one  respiration  to  three  or  four  beats  of  the  heart.  The  same 
relation  is  generally  maintained  in  the  cases  in  which  the  pulse  is  naturally 
accelerated,  as  after  food  or  exercise;  but  in  disease  this  relation  usually 
ceases.  In  many  affections  accompanied  with  increased  frequency  of  the 
pulse,  the  respiration  is,  indeed,  also  accelerated,  yet  the  degree  of  its 
acceleration  may  bear  no  definite  proportion  to  the  increased  number  of 
the  heart's  actions:  and  in  many  other  cases,  the  pulse  becomes  more  fre- 
quent without  any  accompanying  increase  in  the  number  of  respirations; 
or,  the  respiration  alone  may  be  accelerated,  the  number  of  pulsations  re- 
maining stationary,  or  even  falling  below  the  ordinary  standard. 

The  Force  of  the  Ventricular  Systole  and  Diastole.— The 
force  of  the  left  ventricular  systole  is  more  than  double  that  exerted  by  the 
contraction  of  the  right:  this  difference  in  the  amount  of  force  exerted 
by  the  contraction  of  the  two  ventricles,  results  from  the  walls  of  the  left 
ventricle  being  about  twice  or  three  times  as  thick  as  those  of  the  right. 
And  the  difference  is  adapted  to  the  greater  degree  of  resistance  which  the 
left  ventricle  has  to  overcome,  compared  with  that  to  be  overcome  by  the 
right:  the  former  having  to  propel  blood  through  every  part  of  the  body, 
the  latter  only  through  the  lungs. 

The  actual  amount  of  the  intra-ventricular  pressures  during  systole 
in  the  dog  has  been  found  to  be  2 '4  inches  (60  mm.)  of  mercury  in  the 
right  ventricle,  and  6  inches  (150  mm.)  in  the  left.  During  diastole  there 
is  in  the  right  ventricle  a  negative  or  suction  pressure  of  about  |  of  an 
inch  (—17  to  —16  mm.),  and  in  the  left  ventricle  from  2  inches  to  f  of 
an  inch  (—52  to  —20  mm.).  Part  of  this  fall  in  pressure,  and  possibly 
the  greater  part,  is  to  be  referred  to  the  influence  of  respiration;  but  with- 
out this  the  negative  pressure  of  the  left  ventricle  caused  by  its  active 
dilatation  is  about  |  of  an  inch  (23  mm.)  of  mercury. 

The  right  ventricle  is  undoubtedly  aided  by  this  suction  power  of  the 


124 


HAND-BOOK  OF  PHYSIOLOGY. 


left,  so  that  the  whole  of  the  work  of  conducting  the  pulmonary  circula- 
tion does  not  fall  upon  the  right  side  of  the  heart,  but  is  assisted  by  the 
left  side. 

The  Force  of  the  Auricular  Systole  and  Diastole. — The 

maximum  pressure  within  the  right  auricle  is  about  |  of  an  inch  (20  mm.) 
of  mercury,  and  is  probably  somewhat  less  in  the  left.  It  has  been  found 
that  during  diastole  the  pressure  within  both  auricles  sinks  considerably 
below  that  of  the  atmosphere;  and  as  some  fall  in  pressure  takes  place, 
even  when  the  thorax  of  the  animal  operated  upon  has  been  opened,  a 
certain  proportion  of  the  fall  must  be  due  to  active  auricular  dilatation 
independent  of  respiration.  In  the  right  auricle,  this  negative  pressure 
is  about  —10  mm. 

Work  Done  by  the  Heart. — In  estimating  the  work  done  by  any 
machine  it  is  usual  to  express  it  in  terms  of  the  "unit  of  work.^^  The  unit 
of  work  is  defined  to  be  the  energy  expended  in  raising  a  unit  of  weight 
(1  lb.)  through  a  unit  of  height  (1  ft.).  In  England,  the  unit  of  work 
is  the  "foot-pound,''  in  France,  the  ^^Mlogrmmnetre.'' 

The  work  done  by  the  heart  at  each  contraction  can  be  readily  found 
by  multiplying  the  weight  of  blood  expelled  by  the  ventricles  by  the 
height  to  which  the  blood  rises  in  a  tube  tied  into  an  artery.  This  height 
was  found  to  be  about  9  ft.  in  the  horse,  and  the  estimate  is  nearly  correct 
for  a  large  artery  in  man.  Taking  tlie  weight  of  blood. expelled  from  the 
left  ventricle  at  each  systole  as  6  oz.,  i.e.,  |  lb.,  we  have  9  X  f  =  3-375 
foot-pounds  as  the  work  done  by  the  left  ventricle  at  each  systole;  and 
adding  to  this  the  work  done  by  the  right  ventricle  (about  one-tliird  that 
of  the  left)  we  have  3  "375  X  1'125  =  4*5  foot-pounds  as  the  work  done 
by  the  heart  ,  at  each  contraction.  Other  estimates  give  ^  kilogrammetre, 
or  about  3  \  foot-pounds.  Haughton  estimates  the  total  work  of  the  heart 
in  24  hours  as  about  124  foot-tons. 

Influence  of  the  Nervous  System  on  the  Action  of  the 
Heart. — The  hearts  of  warm-blooded  animals  cease  to  beat  almost  if  not 
quite  immediately  after  removal  from  the  body,  and  are,  therefore,  un- 
favorable for  the  study  of  the  nervous  mechanism  which  regulates  their 
action.  Observations  have  hitherto,  therefore,  been  principally  directed 
to  the  lieart  of  cold-blooded  animals,  e.g.,  tlie  frog,  tortoise,  and  snake, 
wliich  will  continue  to  beat  under  favorable  conditions  for  many  hours 
after  removal  from  the  body.  Of  these  animals,  the  frog  is  the  one  mostly 
employed,  and,  indeed,  until  recently,  it  was  from  the  study  of  tlio  frog's 
lieart  that  tlie  chief  })art  of  our  information  was  obtained.  If  removed 
from  the  body  entire,  the  frog's  heart  will  continue  to  beat  for  many  hours 
and  even  days,  and  the  beat  has  no  a})parent  difference  from  the  beat  of 
the  heart  before  removal  from  the  body;  it  will  take  place  without  the 
])reseuce  of  blood  or  other  Ihiid  within  its  chambers.  If  the  bents  have 
become  iiifrcqiunit,  an  additional  beat  may  be  induced  by  stimulating 


CIRCULATION  OF  THE  BLOOD. 


125 


the  heart  by  means  of  a  blunt  needle;  but  the  time  before  the  stimulus 
applied  produces  its  result  (the  latent  period)  is  very  prolonged,  and  as 
in  this  way  the  cardiac  beat  is  like  the  contraction  of  unstriped  muscle, 
the  method  has  been  likened  to  a  peristaltic  contraction. 

There  is  much  uncertainty  about  the  nervous  mechanism  of  the  beat 
of  the  frog's  heart,  but  what  has  just  been  said  shows,  at  any  rate,  two 
things;  firstly,  that  as  the  heart  will  beat  when  removed  from  the  body  in 
a  way  differing  not  at  all  from  the  normal,  it  must  contain  within  itself  the 
mechanism  of  rhythmical  contraction;  and  secondly,  that  as  it  can  beat 
without  the  presence  of  fluid  within  its  chambers,  the  movement  cannot 
depend  merely  on  reflex  excitation  by  the  entrance  of  blood.  The  nervous 
apparatus  existing  in  the  heart  itself  consists  of  collections  of  microscopic 
ganglia,  and  of  nerve- fibres  proceeding  from  them.    These  ganglia  are 


Fig.  106. — Heart  of  frog.  (Burdon-Sanderson  after  Fritsche.)  Front  view  to  the  left,  back  view- 
to  the  right.  A  A.  Aortse.  V.  cs.  Venae  cavae  superiores.  At  s,  left  auricle.  At  d,  right  auricle. 
Fen.,  ventricle.  B.  ar.,  Bulbus  arteriosus.  (S.  v..  Sinus  venosus.  V.  c.  i.,  Vena  cava  inferior.  V. 
h.,  Vense  hepaticae.    V.  p.,  Venae  pulmonales. 

demonstrable  as  being  collected  chiefly  into  three  groups;  one  is  in  the 
wall  of  the  sinus  venosus  (Kemak's);  a  second,  near  the  junction  between 
the  auricle  and  ventricle  (Bidder^s);  and  the  third  in  the  septum  between 
the  auricles. 

Some  very  important  experiments  seem  to  identify  the  rhythmical 
contractions  of  the  frog^s  heart  with  these  ganglia.  If  the  heart  be  re- 
moved entire  from  the  body,  the  sequence  of  the  contraction  of  its  several 
beats  will  take  place  with  rhythmical  regularity,  viz.,  of  the  sinus  veno- 
sus, the  auricles,  the  ventricle,  and  bulbus  arteriosus,  in  order.  If  the 
heart  be  removed  at  the  junction  of  the  sinus  and  auricle,  the  former  will 
continue  to  beat,  but  the  removed  portion  will  for  a  short  variable  time 
stop  beating,  and  then  resume  its  beats,  but  with  a  rhythm  different  to 
that  of  the  sinus:  and,  further,  if  the  ventricle  be  removed,  it  will  take 
a  still  longer  time  before  recommencing  its  pulsation  after  its  removal 
than  the  larger  portion  consisting  of  the  auricles  and  ventricle,  and  its 
rhythm  is  different  from  that  of  the  unremoved  portion,  and  not  so  regu- 
lar, nor  will  it  continue  to  pulsate  so  long:  during  the  period  of  stop- 
page a  contraction  will  occur  if  the  ventricle  be  mechanically  or  otherwise 
stimulated.  If  the  lower  two-thirds  or  apex  of  the  ventricle  be  removed, 
the  remainder  of  the  heart  will  go  on  beating  regularly  in  the  body,  but 


126 


HAND-BOOK  OF  PHYSIOLOGY. 


this  part  will  remain  motionless,  and  will  not  beat  spontaneously,  although 
it  will  respond  to  stimuli.  If  the  heart  be  divided  lengthwise,  its  parts 
will  continue  to  pulsate  rhythmically,  and  the  auricles  may  be  cut  up  into 
pieces,  and  the  pieces  will  continue  their  movements  of  contraction.  It 
will  be  thus  seen  that  the  rhythmical  movements  appear  to  be  more  marked 
in  the  parts  supplied  by  the  ganglia,  and  that  the  apical  portion  of  the 
ventricle,  in  which  the  ganglia  are  not  found,  does  not  possess  the  power 
of  automatic  movement.  Although  the  theory  that  the  pulsations  of  the 
rest  of  the  heart  are  dependent  upon  that  of  the  sinus,  and  to  stimuli  pro- 
ceeding from  it,  when  connection  is  maintained,  and  only  to  reflex  stim- 
uli when  removal  has  taken  place,  cannot  be  absolutely  upheld,  yet  it  is 
evident  that  the  power  of  spontaneous  contraction  is  strongest  in  the 
sinus,  less  strong  in  the  auricles,  and  less  so  still  in  the  ventricle,  and 
that,  therefore,  the  sinus  ganglia  are  probably  important  in  exciting  the 
rhythmical  contraction  of  the  whole  heart.  This  is  expressed  in  the  fol- 
lowing way: — "The  power  of  independent  rhythmical  contraction  de- 
creases regularly  as  we  pass  from  the  sinus  to  the  ventricles, and  "The 
rhythmical  power  of  each  segment  of  the  heart  varies  inversely  as  its  dis- 
tance from  the  sinus."  (G-askell.) 

It  has  been  recently  shown  that,  under  appropriate  stimuli,  even  the 
extreme  apex  of  the  ventricle  in  the  tortoise  may  take  on  rhythmical 
contractions,  or  in  other  words  may  be  "taught  to  beat"  rhythmically. 
(Gaskell.) 

Inhibition  of  the  Heart's  Action. — Although,  under  ordinary 
conditions,  the  apparatus  of  ganglia  and  nerve-fibi'es  in  the  substance 
of  the  heart  forms  the  medium  through  which  its  action  is  excited  and 
rhythmically  maintained,  yet  they,  and,  through  them,  the  hearths  con- 
tractions, are  regulated  by  nerves  which  pass  to  them  from  the  higher 
nerve-centres.  These  nerves  are  branches  from  the  pneumogastric  or 
vagus  and  the  sympathetic. 

The  influence  of  the  vagi  nerves  over  the  heart-beat  may  be  shown  by 
stimulating  one  (especially  the  right)  or  both  of  the  nerves  when  a  record 
is  being  taken  of  the  beats  of  the  frog's  heart.  If  a  single  induction  shock 
be  sent  into  the  nerve,  the  heart,  after  a  short  interval,  ceases  beating, 
but  after  the  suppression  of  several  beats  resumes  its  action.  As  already 
mentioned,  the  effect  of  the  stimulus  is  not  immediately  seen,  and  one  beat 
may  occur  before  the  heart  stops  after  the  application  of  the  electric-cur- 
rent. The  stoppage  of  the  heart  may  occur  apparently  in  one  of  two 
ways,  either  by  diminution  of  the  strength  of  the  systole  or  by  increas- 
ing the  length  of  tlie  diastole.  The  stoppage  of  the  heart  may  be  brought 
about  by  tlie  ai)i)lication  of  the  electrodes  to  any  part  of  the  vagus,  but 
most  e1T('(;tiially  if  thoy  are  api)licd  near  the  ])osition  of  l^eniak's  ganglia. 
It  is  8iq)p()se(l  tliat  the  flbres  of  the  vagi,  tliorefore,  terminate  there  in 


CIRCULATION  OF  THE  BLOOD. 


127 


inhihitory  ganglia  in  the  lieart-walls,  and  that  tlie  inhibition  of  the  heart's 
beats  by  means  of  the  vagus,  is  not  a  simple  action,  but  that  it  is  pro- 
duced by  stimulating  centres  in  the  heart  itself.  These  inhibitory  centres 
are  paralyzed  by  atropin,  and  then  no  amount  of  stimulation  of  the  vagus, 
or  of  the  heart  itself,  will  produce  any  effect  upon  the  cardiac  beats. 
Urari  in  large  doses  paralyzes  the  vagjus  fibres,  but  in  this  case,  as  the 
inhibitory  action  can  be  produced  by  direct  stimulation  of  the  heart,  it  is 
inferred  that  this  drug  does  not  paralyze  the  ganglia  themselves.  Mus- 
carin  and  pilocarpin  appear  to  produce  effects  similar  to  those  obtained 
by  stimulating  the  vagus  fibres. 

If  a  ligature  be  tightly  tied  round  the  heart  over  the  situation  of  the 
ganglia  between  the  sinus  and  the  auricles,  the  heart  stops  beating. 
This  experiment  (Stannius')  would  seem  to  stimulate  the  inhibitory  gan- 
glia, but  for  the  remarkable  fact  that  atropin  does  not  interfere  with  its 
success.  If  the  part  (the  ventricle)  below  the  ligature  be  cut  off,  it  will 
begin  and  continue  to  beat  rhythmically,  this  may  be  explained  by  sup- 
posing that  the  stimulus  of  section  induces  pulsation  in  the  part  which 
is  removed  from  the  influence  of  the  inhibitory  ganglia. 

So  far,  the  effect  of  the  terminal  apparatus  of  the  vagi  has  been  con- 
sidered; there  is,  however,  reason  for  believing  that  the  vagi  nerves  are 
simply  the  media  of  an  inliiMtory  or  restraining  influence  over  the  action 
of  the  heart,  which  is  conveyed  through  them  from  a  centre  in  the  me- 
dulla oblongata  which  is  always  in  operation,  and,  because  of  its  restrain- 
ing the  heart's  action,  is  called  the  cardio-inliibitory  centre.  For,  on 
dividing  these  nerves,  the  pulsations  of  the  heart  are  increased  in  fre- 
quency, an  effect  opposite  to  that  produced  by  stimulation  of  their 
divided  (peripheral)  ends.  The  restraining  influence  of  the  centre  in  the 
medulla  may  be  increased  reflexly,  producing  slowing  or  stoppage  of  the 
heart,  through  influence  passing  from  it  down  the  vagi.  As  an  example 
of  the  latter,  the  well-known  effect  on  the  heart  of  a  violent  blow  on  the 
epigastrium  may  be  referred  to.  The  stoppage  of  the  heart's  action  is  due 
to  the  conveyance  of  the  stimulus  by  fibres  of  the  sympathetic  to  the 
medulla  oblongata,  and  its  subsequent  rejiection  through  the  vagi  to  the 
inhibitory  ganglia  of  the  heart.  It  is  also  believed  that  the  power  of  the 
medullary  inhibitory  centre  may  be  reflexly  lessened,  producing  acceler- 
ated action  of  the  heart. 

Acceleration  of  Heart's  Action. — Through  certain  fibres  of  the 
sympathetic,  the  heart  receives  an  accelerating  influence  from  the  medulla 
oblongata.  These  accelerating  nerve-flbres,  issuing  from  the  spinal  cord 
in  the  neck,  reach  the  inferior  cervical  ganglion,  and  pass  thence  to  the 
cardiac  plexus,  and  so  to  the  heart.  Their  function  is  shown  in  the 
quickened  pulsation  which  follows  stimulation  of  the  spinal  cord,  when 
the  latter  has  been  cut  off  from  all  connection  with  the  heart,  excepting 
that  which  is  formed  by  the  accelerating  filaments  from  the  inferior  cer- 


128 


HAND-BOOK  OF  PHYSIOLOGY. 


vical  ganglion.  Unlike  the  inhibitory  fibres  of  the  pneumogastric,  the 
accelerating  fibres  are  not  continuonsly  in  action. 

The  accelerator  nerves  must  not,  however,  be  considered  as  direct 
antagonists  of  the  vagus;  for  if  at  the  moment  of  their  maximum  stimu- 
lation, the  vagus  be  stimulated  with  minimum  currents,  ijihibition  is 
produced  with  the  same  readiness  as  if  these  were  not  acting. 

The  connection  of  the  heart  with  other  organs  by  means  of  the  nerv- 
ous system,  and  the  influences  to  which  it  is  subject  through  them,  are 
shown  in  a  striking  manner  by  the  phenomena  of  disease.  The  influence 
of  mental  shock  in  arresting  or  modifying  the  action  of  the  heart,  the 
slow  pulsation  which  accompanies  compression  of  the  brain,  the  irregu- 
larities and  palpitations  caused  by  dyspepsia  or  hysteria,  are  good  evidence 
of  the  connection  of  the  heart  with  other  organs  through  the  nervous 
system. 

The  action  of  the  heart  is  no  doubt  also  very  materially  affected  by 
the  nutrition  of  its  walls  by  a  sufiicient  supply  of  healthy  blood  sent  to 
them,  and  it  is  not  unlikely  that  the  apparently  contradictory  effect  of 
poisons  may  be  explained  by  supposing  that  the  influence  of  some  of  them 
is  either  partially  or  entirely  directed  to  the  muscular  tissue  itself,  and 
not  to  the  nervous  apparatus  alone.  As  will  be  explained  presently,  the 
heart  exercises  a  considerable  influence  upon  the  condition  of  the  pressure 
of  blood  within  the  arteries,  but  in  its  turn  the  blood-pressure  within  the 
arteries  reacts  upon  the  heart,  and  has  a  distinct  effect  upon  its  contrac- 
tions, increasing  by  its  increase,  and  vice  versa,  the  force  of  the  cardiac 
beat,  although  the  frequency  is  diminished  as  the  blood-pressure  rises. 
The  quantity  (and  quality?)  of  the  blood  contained  in  each  chamber,  too, 
has  an  influence  upon  its  systole,  and  within  normal  limits  the  larger  the 
quantity  the  stronger  the  contraction.  Kapidity  of  systole  does  not  of 
necessity  indicate  strength,  as  two  weak  contractions  often  do  no  more 
work  than  one  strong  and  prolonged.  In  order  that  the  heart  may  do  its 
maximum  work,  it  must  be  allowed  free  space  to  act;  for  if  obstructed 
in  its  action  by  mechanical  outside  pressure,  as  by  an  excess  of  fluid  within 
the  pericardium,  such  as  is  produced  by  inflammation,  or  by  an  over- 
loaded stomach,  or  what  not,  the  pulsations  become  irregular  and  feeble. 

The  Arteries. 

Distribution. — The  arterial  system  begins  at  the  left  ventricle  in  a 
single  lai'go  trunk,  the  aorta,  which  almost  immediately  after  its  origin 
gives  off  in  its  course  in  the  thorax  three  large  branches  for  the  supply 
of  the  head,  neck,  and  upper  extremities;  it  then  traverses  the  thorax 
and  abdomen,  giving  off  branches,  some  large  and  some  small,  for  tlie 
supply  of  the  various  organs  and  tissues  it  passes  on  its  way.  In  the 
abdomen  it  divides  into  two  chief  branches,  for  the  supply  of  the  lower 


CIRCULATION  OF  THE  BLOOD. 


129 


extremities.  The  arterial  branches  wherever  given  off  divide  and  sub- 
divide, until  the  calibre  of  each  subdivision  becomes  very  minute,  and 
these  minute  vessels  pass  into  capillaries.  Arteries  are,  as  a  rule,  placed 
in  situations  protected  from  pressure  and  other  dangers,  and  are,  with 
few  exceptions,  straight  in  their  course,  and  frequently  communicate  with 
other  arteries  (anastomose  or  inosculate).  The  branches  are  usually 
given  off  at  an  acute  angle,  and  the  area  of  the  branches  of  an  artery  gen- 
erally exceeds  that  of  the  parent  trunk;  and  as  the  distance  from  the 
origin  is  increased,  the  area  of  the  combined  branches  is  increased  also. 

After  death,  arteries  are  usually  found  dilated  (not  collapsed  as  the 
veins  are)  and  empty,  and  it  was  to  this  fact  that  their  name  was  given 
them,  as  the  ancients  believed  that  they  conveyed  air  to  the  various  parts 
of  the  body.  As  regards  the  arterial  system  of  the  lungs  (pulmonary 
system)  it  begins  at  the  right  ventricle  in  the  pulmonary  artery,  and  is 
distributed  much  as  the  arteries  belonging  to  the  general  systemic  cir- 
culation. 

Structure. — The  walls  of  the  arteries  are  composed  of  three  principal 
coats,  termed  the  external  or  tunica  adventitia,  the  middle  or  tunica 
media,  and  the  internal  cosit  or  tunica  intima. 

The  external  coat  or  tunica  adventitia  (Figs.  107  and  111,  t.  a.),  the 
strongest  and  toughest  part  of  the  wall  of  the  artery,  is  formed  of  areolar 


Fig.  107.— Minute  artery  viewed  in  longitudinal  section,  e.  Nucleated  endothelial  membrane, 
vath.  faint  nuclei  in  lumen,  looked  at  from  above,  i.  Thin  elastic  tunica  intima.  m.  Muscular  coat; 
or  tunica  media,   a.  Tunica  adventitia.   (Klein  and  Noble  Smith.)   x  250. 

Fig.  108.— Portion  of  fenestrated  membrane  trom  the  femoral  artery,  x  200.  a,  6,  c.  Perfo- 
rations. (Henle.) 


tissue,  with  which  is  mingled  throughout  a  network  of  elastic  fibres.. 
At  the  inner  part  of  this  outer  coat  the  elastic  network  forms  in  most 
arteries  so  distinct  a  layer  as  to  be  sometimes  called  the  external  elastic 
coat  (Fig.  123,  e.  e.). 

The  middle  coat  (Fig.  107,  m)  is  composed  of  both  muscular  and 
Vol.  I.— 9 


Fig.  107. 


Fig.  108. 


130 


HAND-BOOK  OF  PHYSIOLOGY. 


elastic  fibres,  with  a  certain  proportion  of  areolar  tissue.  In  the  larger 
arteries  (Fig.  110)  its  thickness  is  comparatively  as  well  as  absolutely 
much  greater  than  in  the  small,  constituting,  as  it  does,  the  greater  part 
of  the  arterial  wall. 

The  muscular  fibres,  which  are  of  the  unstriped  variety  (Fig.  109)  are 
arranged  for  the  most  part  transversely  to  the  long  axis  of  the  artery 
(Fig.  107,  m);  while  the  elastic  element,  taking  also  a  transverse  direc- 
tion, is  disposed  in  the  form  of  closely  interwoven  and  branching  fibres, 
which  intersect  in  all  parts  the  layers  of  muscular  fibre.    In  arteries  of 


Fig.  109.  Fig.  110. 

Fig.  109.— Muscular  fibre-cells  from  human  arteries,  magnified  350  diameters.  (Kolliker.)  a. 
Nucleus,    b.  A  fibre-cell  treated  with  acetic  acid. 

Fig.  110.— Transverse  section  of  aorta  through  internal  and  about  half  the  middle  coat.  a.  Lin- 
ing endothelium  with  the  nuclei  of  the  cells  only  shown,  b.  Subepithelial  layer  of  connective  tissue, 
c,  d.  Elastic  tunica  intima  proper,  with  fibrils  rumiing  circularly  or  longitudinally,  e.  f.  Middle  coat, 
consisting  of  elastic  fibres  arranged  longitudinallj',  with  muscle-fibres  cut  obliquely,  or  longitudinallj'. 
(Klein.) 

various  size  there  is  a  difference  in  the  proportion  of  the  muscular  and 
clastic  element,  elastic  tissue  preponderating  in  the  largest  arteries,  while 
this  condition  is  reversed  in  those  of  medium  and  small  size. 

The  internal  coat  is  formed  by  layers  of  elastic  tissue,  consisting  in 
part  of  coarse  longitudinal  branching  fibres,  and  in  part  of  a  very  thin 
and  brittle  mem])rane  which  possesses  little  elasticity,  and  is  thrown  into 
folds  or  wrinkles  when  tlic  artery  contracts.  Tliis  latter  monibrano, 
the  striated  or  fenestrated  coat  of  Iloilr  (1^'ig.  lOS),  is  peculiar  in  its  ten- 
d(5ncy  to  cnrl  up,  when  ])eekHl  olT  I'roni  (he  artery,  and  in  the  perforated 


CIRCULATION  OF  THE  BLOOD. 


131 


and  streaked  appearance  which  it  presents  under  the  microscope.  Its 
inner  surface  is  lined  with  a  delicate  layer  of  endothelium,  composed  of 
elongated  cells  (Fig.  112,  a),  which  make  it  smooth  and  polished,  and 
furnish  a  nearly  impermeable  surface,  along  which  the  blood  may  flow 
with  the  smallest  possible  amount  of  resistance  from  friction. 

Immediately  external  to  the  endothelial  lining  of  the  artery  is  fine 
connective  tissue,  suh-endotlielial  layer,  with  branched  corpuscles.  Thus 
the  internal  coat  consists  of  three  parts,  {a)  an  endothelial  lining,  {h)  the 
sub-endothelial  layer,  and  {c)  elastic  layers. 

Vasa  Vasorum. — The  walls  of  the  arteries,  with  the  possible  excep- 
tion of  the  endothelial  lining  and  the  layers  of  the  internal  coat  immedi- 
ately outside  it,  are  not  nourished  by  the  blood  which  they  convey,  but 
are,  like  other  parts  of  the  body,  supplied  with  little  arteries,  ending  in 


Fig.  111. — Transverse  section  of  small  artery  from  soft  palate,  e,  endothelial  lining,  the  nuclei 
of  the  cells  are  shown;  i,  elastic  tissue  of  the  intima,  which  is  a  good  deal  folded;  c.  m.  circular  mus- 
cular coat,  showing  nuclei  of  muscle  cells;  t.  a.  timica adventitia.    X  300.  (Schofield.) 

Fig.  112.— Two  blood-vessels  from  a  frog's  mesentery,  injected  with  nitrate  of  silver,  showing  the 
outlines  of  the  endothelial  cells,  a.  Artery.  The  endothelial  cells  are  long  and  narrow;  the  trans- 
verse markings  indicate  the  muscular  coat.  t.  a.  Tunica  adventitia.  v.  Vein,  showing  the  shorter 
and  wider  endothehal  ceUs  with  which  it  is  lined,   c,  c.  Two  capillaries  entering  the  vein.  (Schofield.) 


capillaries  and  veins,  which,  branching  throughout  the  external  coat, 
extend  for  some  distance  into  the  middle,  but  do  not  reach  the  internal 
coat.    These  nutrient  vessels  are  called  vasa  vasorum. 

Lymphatics  of  Arteries  and  Veins. — Lymphatic  spaces  are  pres- 
ent in  the  coats  of  both  arteries  and  veins;  but  in  the  tunica  adventitia 
or  external  coat  of  large  vessels  they  form  a  distinct  plexus  of  more  or  less 
tubular  vessels.  In  smaller  vessels  they  appear  as  sinous  spaces  lined  by 
endothelium.  Sometimes,  as  in  the  arteries  of  the  omentum,  mesentery, 
and  membranes  of  the  brain,  in  the  pulmonary,  hepatic,  and  splenic 
arteries,  the  spaces  are  continuous  with  vessels  which  distinctly  ensheath 


Fig.  111. 


Fig.  112, 


132 


HAND-BOOK  OF  PHYSIOLOGY. 


them— perivascular  lympliatic  sheaths  (Fig.  121).  Lymph  channels  are 
said  to  be  present  also  in  the  tunica  media. 

Nervi  Vasorum. — Most  of  the  arteries  are  surrounded  by  a  plexus 
of  sympathetic  nerves^  which  twine  around  the  vessel  very  much  like  ivy 
round  a  tree:  and  ganglia  are  found  at  frequent  intervals.    The  smallest 


Fig.  113.— Blood-vessels  from  mesocolon  of  rabbit,  a.  Artery,  with  two  branches,  showing  tr.  n. 
nuclei  of  transverse  muscular  fibres;  I.  n.  nuclei  of  endothelial  lining;  t.  a.  tunica  adventitia.  v. 
Vein.  Here  the  transverse  nuclei  are  more  oval  than  those  of  the  artery.  The  vein  receives  a  small 
branch  at  the  lower  end  of  the  drawing;  it  is  distinguished  from  the  artery  among  other  things  by  its 
straighter  course  and  larger  calibre,  c.  Capillary,  showing  nuclei  of  endotheUal  cells.  X  300. 
(Schofleld.) 

arteries  and  capillaries  are  also  surrounded  by  a  very  delicate  network  of 
similar  nerve-fibres,  many  of  which  appear  to  end  in  the  nuclei  of  the 
transverse  muscular  fibres  (Fig.  122).  It  is  through  these  plexuses  that 
the  calibre  of  the  vessels  is  regulated  by  the  nervous  system  (p.  152). 

The  Capillaries. 

Distribution. — In  all  vascular  textures,  except  some  parts  of  the 
corpora  cavernosa  of  the  penis,  and  of  the  uterine  placenta,  and  of  the 
spleen,  the  transmission  of  the  blood  from  the  minute  branches  of  the 
arteries  to  the  minute  veins  is  effected  through  a  network  of  ')nicroscoj){e 
vessels,  called  capillaries.  These  may  be  seen  in  nil  minutely  injected 
preparations;  and  during  life,  in  any  trans})arent  vascular  parts, — such 
as  the  web  of  the  frog's  foot,  the  tail  or  external  bruiichiiv  of  the  tadpole, 
or  the  wing  of  the  bat. 

Tlic  branches  of  the  minute  arteries  form  repeated  anastomoses  witli 


CIKC  UL ATION  OF  THE  HLOOD. 


133 


each  other,  and  give  off  tlie  capillaries  which,  hy  their  anastomoses,  com- 
pose a  continuous  and  uniform  network,  from  which  the  venous  radicles 
take  their  rise  (Fig.  114).  The  i)oint  at  wliich  the 
arteries  terminate  and  the  minute  veins  commence, 
cannot  be  exactly  defined,  for  the  transition  is 
gradual;  but  the  capillary  network  has,  neverthe- 
less, this  peculiarity,  tliat  the  small  vessels  wliich 
compose  it  maintain  the  same  diameter  throughout: 
they  do  not  diminish  in  diameter  in  one  direction, 
like  arteries  and  veins;  and  the  meshes  of  the  net- 
work that  they  compose  are  more  uniform  in  shape 
and  size  than  those  formed  by  the  anastomoses  of 
the  minute  arteries  and  veins. 

Structure. — This  is  much  more  simple  than 
that  of  the  arteries  or  veins.  Their  walls  are  com- 
posed of  a  single  layer  of  elongated  or  radiate,  flat- 
tened and  nucleated  cells,  so  joined  and  dovetailed 
together  as  to  form  a  continuous  transparent  mem- 
brane (Fig.  115).  Outside  these  cells,  in  the  larger 
capillaries,  there  is  a  structureless,  or  very  finely 
fibrillated  membrane,  on  the  inner  surface  of  which 
they  are  laid  down. 

In  some  cases  this  external  membrane  is  nu- 
cleated, and  may  then  be  regarded  as  a  miniature  representative  of  the 
tunica  adventitia  of  arteries. 

Here  and  there,  at  the  junction  of  two  or  more  of  the  delicate  endo- 
thelial cells  which  compose  the  capillary  wall,  ^Jseudo-sto^naf a  may  be  seen 


Fig.  114.— Blood-vessels  of 
an  intestinal  villus,  repre- 
senting the  arrangement  of 
capillaries  between  the  ulti- 
mate venous  and  arterial 
branches;  a,  a,  the  arteries; 
b,  the  vein. 


Fig.  115.— Capillary  blood-vessels  from  the  omentum  of  rabbit,  showing  the  nucleated  endothe- 
lial membrane  of  which  they  are  composed.    (Klein  and  Noble  Smith.) 

resembling  those  in  serous  membranes  (p.  296).  The  endothelial  cells  are 
often  continuous  at  various  points  with  processes  of  adjacent  connective- 
tissue  corpuscles. 


134 


HAND-BOOK  OF  PHYSIOLOGY. 


Capillaries  are  surrounded  by  a  delicate  nerve-plexus  resembling,  in 
miniature,  that  of  the  larger  blood-vessels. 

The  diameter  of  the  capillary  vessels  varies  somewhat  in  the  different 
textures  of  the  body,  the  most  common  size  being  about  -g-o-Fo^^^ 
inch.    Among  the  smallest  may  be  mentioned  those  of  the  brain,  and 
of  the  follicles  of  the  mucous  membrane  of  the  intestines ;  among  the 
largest,  those  of  the  skin,  and  especially  those  of  the  medulla  of  bones. 

The  size  of  capillaries  varies  necessarily  in  different  animals  in  relation 
to  the  size  of  their  blood  corpuscles:  thus,  in  the  Proteus,  the  capillary 
circulation  can  Just  be  discerned  with  the  naked  eye. 

The  form  of  the  capillary  network  presents  considerable  variety  in  the 
different  textures  of  the  body:  the  varieties  consisting  principally  of  modi- 
fications of  two  chief  kinds  of  mesh,  the  rounded  and  the  elongated.  That 


kind  of  which  the  meshes  or  interspaces  have  a  roundish  form  is  the  most 
common,  and  prevails  in  those  parts  in  which  the  capillary  network  is 
most  dense,  such  as  the  lungs  (Fig.  IIG),  most  glands,  and  mucous  mem- 
branes, and  the  cutis.  The  meshes  of  this  kind  of  network  are  not  quite 
circular  but  more  or  less  angular,  sometimes  presenting  a  nearly  regular 
quadrangular  or  polygonal  form,  but  being  more  frequently  irregular. 
The  capillary  network  witli  elongated  meshes  (Fig.  117)  is  observed  in 
parts  in  which  the  vessels  are  arranged  among  bundles  of  fine  tubes  or 
fibres,  as  in  muscles  aiul  nerves.  In  such  parts,  the  meshes  usually  have 
the  form  of  a  parallelogram,  the  short  sides  of  whicli  may  be  from  three 
to  eiglit  or  ten  times  less  than  tlie  long  ones;  the  long  sides  always  corre- 
sponding to  the  axis  of  the  fibre  or  tube,  by  whicli  it  is  ])laced.  The  ap- 
pearaii{'(^  of  both  Ihc  rouiuh'd  mul  (doiigatcd  iiH'sh(>s  is  much  varied 


CIRCULATION  OF  THE  BLOOD. 


135 


according  as  the  vessels  composing  them  have  a  straight  or  tortuous  form. 
Sometimes  the  capillaries  have  a  looped  arrangement,  a  single  capillary 
projecting  from  the  common  network  into  some  prominent  organ,  and 
returning  after  forming  one  or  more  loops,  as  in  the  papillae  of  the  tongue 
and  skin. 

The  number  of  the  capillaries  and  the  size  of  the  meshes  in  different 
parts  determine  in  general  the  degree  of  vascularity  of  those  parts.  The 
parts  in  which  the  network  of  capillaries  is  closest,  that  is,  in  which  the 
meshes  or  interspaces  are  the  smallest,  are  the  lungs  and  the  choroid 
membrane  of  the  eye.  In  the  iris  and  ciliary  body,  the  interspaces  are 
somewhat  wider,  yet  very  small.  In  the  human  liver  the  interspaces  are 
of  the  same  size  or  even  smaller  than  the  capillary  vessels  themselves. 
In  the  human  lung  tliey  are  smaller  than  the  vessels;  in  the  human 
kidney,  and  in  the  kidney  of  the  dog,  the  diameter  of  the  injected  capil- 
laries, compared  with  that  of  the  interspaces,  is  in  the  proportion  of  one 
to  four,  or  of  one  to  three.  The  brain  receives  a  very  large  quantity  of 
blood;  but  the  capillaries  in  which  the  blood  is  distributed  through  its 
substance  are  very  minute,  and  less  numerous  than  in  some  other  parts. 
Their  diameter,  according  to  E.  H.  Weber,  compared  with  the  long  diam- 
eter of  the  meshes,  being  in  the  proportion  of  one  to  eight  or  ten ;  com- 
pared with  the  transverse  diameter,  in  the  proportion  of  one  to  four  or 
six.  In  the  mucous  membranes — for  example  in  the  conjunctiva  and  in 
the  cutis  vera,  the  capillary  vessels  are  much  larger  than  in  the  brain, 
and  the  interspaces  narrower, — namely,  not  more  than  three  or  four  times 
wider  than  the  vessels.  In  the  periosteum  the  meshes  are  much  larger. 
In  the  external  coat  of  arteries,  the  width  of  the  meshes  is  ten  times  that 
of  the  vessels  (Henle). 

It  may  be  held  as  a  general  rule,  that  the  more  active  the  functions  of 
an  organ  are,  the  more  vascular  it  is.  Hence  the  narrowness  of  the  inter- 
spaces in  all  glandular  organs,  in  mucous  membranes,  and  in  growing 
parts;  their  much  greater  width  in  bones,  ligaments,  and  other  very 
tough  and  comparatively  inactive  tissues;  and  the  usually  complete 
absence  of  vessels  in  cartilage,  and  such  parts  as  those  in  which,  prob- 
ably, very  little  vital  change  occurs  after  they  are  once  formed. 

The  Veiks. 

Distribution. — The  venous  system  begins  in  small  vessels  which  are 
slightly  larger  than  the  capillaries  from  which  they  spring.  These  vessels 
are  gathered  up  into  larger  and  larger  trunks  until  they  terminate  (as 
regards  the  systemic  circulation)  in  the  two  venae  cavae  and  the  coronary 
veins,  which  enter  the  right  auricle,  and  (as  regards  the  pulmonary  circu- 
lation) in  four  pulmonary  veins,  which  enter  the  left  auricle.  The  capac- 
ity of  the  veins  diminishes  as  they  approach  the  heart;  but,  as  a  rule. 


136 


HAND-BOOK  OF  PHYSIOLOGY. 


the  capacity  of  the  veins  exceeds  by  several  times  (twice  or  three  times) 
that  of  their  corresponding  arteries.  The  pulmonary  veins,  however, 
are  an  exception  to  this  rule,  as  they  do  not  exceed  in  capacity  the 
pulmonary  arteries.  The  veins  are  found  after  death  as  a  rule  to  be  more 
or  less  collapsed,  and  often  to  contain  blood.  The  veins  are  usually  dis- 
tributed in  a  superficial  and  a  deep  set  which  communicate  frequently  in 
their  course. 

Structure. — In  structure  the  coats  of  veins  bear  a  general  resem- 
blance to  those  of  arteries  (Fig.  118).     Thus,  they  possess  an  outer, 


Fig.  118.— Transverse  section  through  a  small  artery  and  vein  of  the  mucous  membrane  of  a 
child's  epiglottis:  the  contrast  between  the  thick--s\  alled  artery  and  the  thin-walled  vein  is  well  shown. 
A.  Artery,  the  letter  is  placed  in  the  lumen  of  the  vessel,  e.  Endothelial  cells  with  nuclei  clearly  vis- 
ible: these  cells  appear  xevy  thick  from  the  contracted  state  of  the  vessel.  Outside  it  a  double  wavy 
hne  marks  the  elastic  tunica  intima.  )n.  Tunica  media  forming  the  chief  part  of  arterial  wall  and 
consisting  of  unstriped  muscular  fibres  circularly  arranged:  their  nuclei  are  well  seen,  a.  Part  of 
the  tunica  adventitia  showing  bundles  of  connective-tissue  fibres  in  section,  with  the  circidar  nuclei 
of  the  connective-tissue  corpuscles.  This  ccxit  gi-adually  merges  into  the  surrounding  connective- 
tissue,  v.  In  the  lumen  of  the  vein.  The  other  letters  indicate  the  same  as  in  the  artery.  The  mus- 
cular coat  of  the  vein  {ta)  is  seen  to  be  much  thimier  than  that  of  the  artery,  x  350.  (^Kleiii  and 
Noble  Smith.) 

middle,  and  infernal  coat.  The  outer  coat  is  constructed  of  areolar  tissue 
like  that  of  the  arteries,  but  is  thicker.  In  some  veins  it  contains  mus- 
cular fibre-cells,  which  are  arranged  longitudinally. 

The  middle  coat  is  considenibly  thinner  tlian  that  of  the  arteries;  and, 
although  it  contains  circular  unstriped  muscular  fibres  or  fibre-cells,  these 
are  mingled  with  a  larger  proportion  of  yellow  elastic  and  white  fibrous 
tissue.  In  the  large  veins,  near  the  heart,  namely  the  ronv  cava'  and 
ptilmonary  veins,  tlie  middle  coat  is  replaced,  for  some  distance  from  the 
lu^art,  by  circularly  arranged  stri])ed  muscular  libres,  continuous  with 
those  of  the  aui'icles. 


CIRCULATION  OF  THE  BLOOD. 


The  internal  coat  of  veins  is  less  brittle  than  the  corresponding  coat 
of  an  artery,  but  in  other  respects  resembles  it  closely. 

Valves. — The  chief  influence  which  the  veins  have  in  the  circulation, 
is  effected  with  the  help  of  the  valves^  which  are  placed  in  all  veins  sub- 
ject to  local  pressure  from  the  muscles  between  or  near  which  they  run. 
The  general  construction  of  these  valves  is  similar  to  that  of  the  semi- 
lunar valves  of  the  aorta  and  pulmonary  artery,  already  described;-  but 
their  free  margins  are  turned  in  the  opposite  direction,  i.e.,  toward  the 
heart,  so  as  to  stop  any  movement  of  blood  backward  in  the  veins.  They 
are  commonly  placed  in  pairs,  at  various  distances  in  different  veins,  but 
almost  uniformly  in  each  (Fig.  119).  In  the  smaller  veins,  single  valves 
are  often  met  with;  and  three  or  four  are  sometimes  placed  together,  or 
near  one  another,  in  the  largest  veins,  such  as  the  subclavian,  and  at 
their  junction  with  the  jugular  veins.    The  valves  are  semilunar;  the 


A  B  C 


Fig.  119.— Diagram  showing  valves  of  veins,  a,  part  of  a  vein  laid  open  and  spread  out.  with  two 
pairs  of  valves,  b.  Longitudinal  section  of  a  vein,  showing  the  apposition  of  the  edges  of  the  valves 
in  their  closed  state,  c,  portion  of  a  distended  vein,  exhibiting  a  sweUing  in  the  situation  of  a  pair 
of  valves. 

unattached  edge  being  in  some  examples  concave,  in  others  straight. 
They  are  composed  of  inextensile  fibrous  tissue,  and  are  covered  with 
endothelium  like  that  lining  the  veins.  During  the  period  of  their  in- 
action, when  the  venous  blood  is  flowing  in  its  proper  direction,  they 
lie  by  the  sides  of  the  veins;  but  when  in  action,  they  close  together  like 
the  valves  of  the  arteries,  and  offer  a  complete  barrier  to  any  backward 
movement  of  the  blood  (Figs.  119  and  120).  Their  situation  in  the 
superficial  veins  of  the  forearm  is  readily  discovered  by  pressing  along  its 
surface,  in  a  direction  opposite  to  the  venous  current,  i.e.,  from  the 
elbow  toward  the  wrist;  when  little  swellings  (Fig.  119,  c)  appear  in  the 
position  of  each  pair  of  valves.  These  swellings  at  once  disappear  when 
the  pressure  is  relaxed. 

Valves  are  not  equally  numerous  in  all  veins,  and  in  many  they  are 
absent  altogether.  They  are  most  numerous  in  the  veins  of  the  extremi- 
ties, and  more  so  in  those  of  the  leg  than  the  arm.  They  are  commonly 
absent  in  veins  of  less  than  a  line  in  diameter,  and,  as  a  general  rule. 


138 


HAND-BOOK  OF  PHYSIOLOGY. 


there  are  few  or  none  in  those  which  are  not  subject  to  muscular  pressure. 
Among  those  veins  which  have  no  valves  may  be  mentioned  the  superior 
and  inferior  vena  cava,  the  trunk  and  branches  of  the  portal  vein,  the 


A  B 


Fig.  120. — A,  vein  with  valves  open,  b,  vein  with  valves  closed:  stream  of  blood  passing  off  by 
lateral  channel.  (Dalton.) 

hepatic  and  renal  veins,  and  the  pulmonary  veins;  those  in  the  interior 
of  the  cranium  and  vertebral  column,  those  of  the  bones,  and  the  trunk 
and  branches  of  the  umbilical  vein  are  also  destitute  of  valves. 

Circulation-  iiq-  the  Arteries. 

Functions  of  the  External  Coat  of  Arteries. — The  external  coat 
forms  a  strong  and  tough  investment,  which,  though  capiible*  of  exten- 
sion, appears  principally  designed  to  strengthen  the  arteries  and  to  guard 
against  their  excessive  distension  by  the  force  of  the  heart's  action.  It  is 
this  coat  which  alone  prevents  the  complete  severance  of  an  artery  Avlien 
a  ligature  is  tightly  applied;  the  internal  and  middle  coats  being  divided. 
In  it,  too,  the  little  vasa  vasorum  (p.  131)  find  a  suitable  tissue  in  which 
to  subdivide  for  tlie  supply  of  tlie  arterial  coats. 

Functions  of  the  Elastic  Tissue  in  Arteries. — Tlic  purpose  of 
the  elastic  tissue,  which  enters  so  largely  into  tlie  formation  of  all  the 
coats  of  tlie  arteries,  is,  (a)  to  guard  the  arteries  from  the  suddenly 
exerted  pressure  to  which  they  are  subjected  at  each  contraction  of  the 
ventricles.  In  every  such  contraction,  the  contents  of  the  ventricles  are 
for(;ed  into  the  arteries  more  quickly  than  they  can  bo  discharged  into 
and  through  the  capillaries.  The  blood  therefore,  being,  for  an  instant, 
resisted  in  its  onward  (bourse,  a  part  of  the  force  with  which  it  was  im- 


CIRCULATION  OF  THE  JiLOOD. 


139 


pelled  is  directed  against  the  sides  of  the  arteries;  under  tliis  force  their 
elastic  walls  dilate,  stretching  enough  to  receive  the  blood,  and  as  they 
stretch,  becoming  more  tense  and  more  resisting.  Thus,  by  yielding, 
they  break  the  shock  of  the  force  impelling 
the  blood.  On  the  subsidence  of  the  pressure, 
when  the  ventricles  cease  contracting,  the  arte- 
ries are  able,  by  the  same  elasticity,  to  resume 
their  former  calibre;  (b)  It  equalizes  the  cur- 
rent of  the  blood  by  maintaining  pressure  on 
it  in  the  arteries  during  the  periods  at  which 
the  ventricles  are  at  rest  or  dilating.  If  the 
arteries  had  been  rigid  tubes,  the  blood,  in- 
stead of  flowing,  as  it  does,  in  a  constant 
stream,  would  have  been  propelled  through 
the  arterial  system  in  a  series  of  jerks  corre- 
sponding to  the  ventricular  contractions,  with 
intervals  of  almost  complete  rest  during  the 
inaction  of  the  ventricles.  -But  in  the  actual 
condition  of  the  arteries,  the  force  of  the  suc- 
cessive contractions  of  the  ventricles  is  ex- 
pended partly  in  the  direct  propulsion  of  the 
blood,  and  partly  in  the  dilatation  of  the  elastic 
arteries;  and  in  the  intervals  between  the  con- 
tractions of  the  ventricles,  the  force  of  the  re- 
coil is  employed  in  continuing  the  same  direct 
propulsion.  Of  course,  the  pressure  they  ex- 
ercise is  equally  diffused  in  every  direction, 
and  the  blood  tends  to  move  backward  as  well 
as  onward,  but  all  movement  backward  is  pre- 
vented by^  the  closure  of  the  semilunar  arterial  valves  (p.  114),  Avhich 
takes  place  at  the  very  commencement  of  the  recoil  of  the  arterial  walls. 

By  this  exercise  of  the  elasticity  of  the  arteries,  all  the  force  of  the 
ventricles  is  made  advantageous  to  the  circulation;  for  that  part  of  their 
force  which  is  expended  in  dilating  the  arteries,  is  restored  in  full  when 
they  recoil.  There  is  thus  no  loss  of  force;  but  neither  is  there  any  gain, 
for  the  elastic  walls  of  the  artery  cannot  originate  any  force  for  the  ^^ropul- 
sion  of  the  blood — they  only  restore  that  which  they  received  from  the 
ventricles.  The  force  v/ith  which  the  arteries  are  dilated  every  time  the 
ventricles  contract,  might  be  said  to  be  received  by  them  in  store,  to  be  all 
given  out  again  in  the  next  succeeding  period  of  dilatation  of  the  ventricles. 
It  is  by  this  equalizing  influence  of  the  successive  branches  of  every  artery 
that,  at  length,  the  intermittent  accelerations  produced  in  the  arterial 
current  by  the  action  of  the  heart,  cease  to  be  observable,  and  the  jetting 
stream  is  converted  into  the  continuous  and  equable  movement  of  the 


Fig.  121. —  Surface  view  of  an 
artery  from  the  mesentery  of  a 
f  rog,'ensheathed  in  a  perivascular 
lyrnphatic  vessel,  a.  The  artery, 
with  its  circular  muscular  coat 
(media)  indicated  by  broad  trans- 
verse markings,  with  an  indication 
of  the  adventitia  outside.  I.  Lym- 
phatic vessel ;  its  wall  is  a  simple 
endothelial  membrane.  (Klein  and 
Noble  Smith.) 


140 


HAND-BOOK  OF  PHYSIOLOGY. 


blood  which  we  see  in  the  capillaries  and  veins.  In  the  production  of  a 
continuous  stream  of  blood  in  the  smaller  arteries  and  capillaries,  the 
resistance  which  is  offered  to  the  blood-stream  in  these  vessels  (p.  158), 
is  a  necessary  agent.  Were  there  no  greater  obstacle  to  the  escape  of 
blood  from  the  larger  arteries  than  exists  to  its  entrance  into  them  from 
the  heart,  the  stream  would  be  intermittent,  notwithstanding  the  elas- 
ticity of  the  walls  of  the  arteries. 

(c.)  By  means  of  the  elastic  tissue  in  their  walls  (and  of  the  muscular 
tissue  also),  the  arteries  are  enabled  to  dilate  and  contract  readily  in  cor- 
respondence with  any  temporary  increase  or  diminution  of  the  total 
quantity  of  blood  in  the  body;  and  within  a  certain  range  of  diminution 


Fig.  122.  Fig.  123. 

Fig.  122.— Ramification  of  nerves  and  termination  in  the  muscvilar  coat  of  a  small  arterj-  of  the 
frog.  (Arnold.) 

Fig.  123.— Transverse  section  through  a  large  branch  of  the  inferior  mesenteric  aj'teiy  of  a  pig. 
e,  endothelial  membrane;  i,  tunica  elastica  interna,  no  subendothehal  layer  is  seen;  >»,  muscular  tu- 
nica media,  containing  only  a  few  wavy  elastic  fibres;  ee.  tunica  elastica  externa,  dividing  the  media 
from  the  connective  tissue  adventitia,  a.   (Klein  and  Noble  Smith.)    x  350. 

of  the  quantity,  still  to  exercise  due  pressure  on  their  contents;  {d.)  The 
elastic  tissue  assists  in  restoring  the  normal  state  after  dimimition  of  its 
calibre,  whether  this  has  been  caused  by  a  contraction  of  the  muscular 
coat,  or  the  temporary  application  of  a  compressing  force  from  without. 
This  action  is  well  shown  in  arteries  which,  having  contracted  by  means 
of  their  muscular  clement,  after  death,  regain  their  average  patency  on 
the  cessation  of  post-mortem  rigidity  (p.  14:2).  (e.)  By  means  of  their 
elastic  coat  the  arteries  are  enabled  to  adapt  themselves  to  the  different 
movemcTits  of  the  several  ])arts  of  the  body. 

Tc)is{())i.  of  Arteries. — Tlio  natural  state  of  all  arteries,  in  regard  at  least 
to  theii-  l(»ngth,  is  onc^  of  tension — they  are  always  more  or  less  stretched, 
and  (>ver  ready  to  recoil  by  virtue  of  tluMr  (>last icily,  whenever  the  opjios- 


CIRCULATION  OF  THE  liLOOD. 


141 


ing  force  is  removed.  The  extent  to  which  the  divided  extremities  of 
arteries  retract  is  a  measure  of  this  tension,  not  of  their  elasticity.  (Savory. ) 

Functions  of  the  Muscular  Coat. — The  most  important  office  of 
the  muscular  coat  is,  (1)  that  of  regulating  the  quantity  of  blood  to  be 
received  by  each  part  or  organ,  and  of  adjusting  it  to  the  requirements 
of  each,  according  to  various  circumstances,  but,  chiefly,  according  to  the 
activity  with  which  the  functions  of  each  are  at  dilferent  times  performed. 
The  amount  of  work  done  by  each  organ  of  the  body  varies  at  different 
times,  and  the  variations  often  quickly  succeed  each  other,  so  that,  as  in 
the  brain,  for  example,  during  sleep  and  waking,  within  the  same  hour 
a  part  may  be  now  very  active  and  then  inactive.  In  all  its  active  exer- 
cise of  function,  such  a  part  requires  a  larger  supply  of  blood  than  is  suffi- 
cient for  it  during  the  times  when  it  is  comparatively  inactive.  It  is  evi 
dent  that  the  heart  cannot  regulate  the  supply  to  each  part  at  different 
periods;  neither  could  this  be  regulated  by  any  general  and  uniform  con- 
traction of  the  arteries;  but  it  may  be  regulated  by  the  power  which  the 
arteries  of  each  part  have,  in  their  muscular  tissue,  of  contracting  so  as 
to  diminish,  and  of  passively  dilating  or  yielding  so  as  to  permit  an  in- 
crease of  the  supply  of  blood,  according  to  the  requirements  of  the  part  to 
which  they  are  distributed.  And  thus,  while  the  ventricles  of  the  heart 
determine  the  total  quantity  of  blood,  to  be  sent  onward  at  each  contrac- 
tion, and  the  force  of  its  propulsion,  and  while  the  large  and  merely  elastic 
arteries  distribute  it  and  equalize  its  stream,  the  smaller  arteries,  in  addi- 
tion, regulate  and  determine,  by  means  of  their  muscular  tissue,  the  propor- 
tion of  the  whole  quantity  of  blood  which  shall  be  distributed  to  each  part. 

It  must  be  remembered,  however,  that  this  regulating  function  of  the 
arteries  is  itself  governed  and  directed  by  the  nervous  system  (vaso-motor 
centres  and  fibres). 

Another  function  of  the  muscular  element  of  the  middle  coat  of  arteries 
is  (2),  to  co-operate  with  the  elastic  in  adapting  the  calibre  of  the  ves- 
sels to  the  quantity  of  blood  which  they  contain.  For  the  amount  of 
fluid  in  the  blood-vessels  varies  very  considerably  even  from  hour  to  hour, 
and  can  never  be  quite  constant;  and  were  the  elastic  tissue  only  present, 
the  pressure  exercised  by  the  walls  of  the  containing  vessels  on  the  con- 
tained blood  would  be  sometimes  very  small,  and  sometimes  inordinately 
great.  The  presence  of  a  muscular  element,  however,  provides  for  a 
certain  uniformity  in  the  amount  of  pressure  exercised;  and  it  is  by  this 
adaptive,  uniform,  gentle,  muscular  contraction,  that  the  normal  tone  of  the 
blood-vessels  is  maintained.  Deficiency  of  this  tone  is  the  cause  of  the 
soft  and  yielding  pulse,  and  its  unnatural  excess,  of  the  hard  and  tense  one. 

The  elastic  and  muscular  contraction  of  an  artery  may  also  be  regarded 
as  fulfilling  a  natural  purpose  when  (3),  the  artery  being  cut,  it  first  limits 
and  then,  in  conjunction  with  the  coagulated  fibrin,  arrests  the  escape  of 
blood.  It  is  only  in  consequence  of  such  contraction  and  coagulation  that 


142 


HAXD-BOOK  OF  PHYSIOLOGY. 


we  are  free  from  danger  througli  even  very  slight  wounds;  for  it  is  only 
when  the  artery  is  closed  that  the  processes  for  the  more  permanent  and 
secure  j)reYention  of  bleeding  are  established. 

(4)  There  appears  no  reason  for  supposing  that  the  muscular  coat 
assists,  to  more  than  a  very  small  degi'ee,  in  ^Dropelling  the  onward  current 
of  blood. 

(1.)  When  a  small  artery  in  the  living  subject  is  exposed  to  the  air  or 
cold,  it  gradually  but  manifestly  contracts.  Hunter  observed  that  the 
posterior  tibial  artery  of  a  dog  when  laid  bare,  became  in  a  short  time  so 
much  contracted  as  almost  to  jorevent  the  transmission  of  blood;  and  the 
observation  has  been  often  and  variously  confirmed.  Simple  elasticity 
could  not  effect  this. 

(2.)  When  an  artery  is  cut  across,  its  divided  ends  contract,  and  the 
orifices  may  be  com^Dletely  closed.  The  rapidity  and  completeness  of  this 
contraction  vary  in  different  animals;  they  are  generally  greater  in  young 
than  in  old  animals;  and  less,  a^D^^arently,  in  man  than  in  the  lower  ani- 
mals. This  contraction  is  due  in  part  to  elasticity,  but  in  part,  also,  to 
muscular  action;  for  it  is  generally  increased  by  the  application  of  cold, 
or  of  any  simple  stimulating  substances,  or  by  mechanically  irritating  the 
cut  ends  of  the  artery,  as  by  pickinsj  or  twisting  them. 

(3.)  The  contractile  property  of  arteries  continues  many  hours  after 
death,  and  thus  affords  an  opportunity  of  distinguishing  it  from  their 
elasticity.  When  a  portion  of  an  artery  of  a  recently  killed  animal  is  ex- 
posed, it  gradually  contracts,  and  its  canal  may  be  thus  completely  closed: 
in  this  contracted  state  it  remains  for  a  time,  varying  from  a  few  hours 
to  two  days:  then  it  dilates  again,  and  i^ermanently  retains  the  same  size. 

This  persistence  of  the  contractile  j^roperty  after  death  was  well  shown 
in  an  observation  of  Hunter,  which  may  be  mentioned  as  proving,  also, 
the  greater  degree  of  contractility  possessed  by  the  smaller  than  by  the 
larger  arteries.  Having  injected  the  uterus  of  a  cow,  which  had  been 
removed  from  the  animal  upward  of  twenty-four  hours,  he  found,  aftei 
the  lapse  of  another  day,  that  the  larger,  vessels  had  become  much  more 
turgid  than  when  he  injected  them,  and  that  the  smaller  arteries  had 
contracted  so  as  to  force  the  injection  back  into  the  larger  ones. 

The  Pulse. 

If  one  extremity  of  an  elastic  tube  be  fastened  to  a  syringe,  and  the 
other  be  so  constricted  as  to  present  an  obstacle  to  the  escape  of  fluid, 
we  shall  have  a  rough  model  of  what  is  present  in  the  living  body: — The 
syringe  representing  the  heart,  the  elastic  tube  the  arteries,  and  the  con- 
tracted oritice  the  arterioles  (smallest  arteries)  and  capillaries.  If  the 
apparatus  be  filled  with  water,  aVid  if  a  fiugcr-lip  be  placed  on  any 
part  of  the  elastic  tube,  there  will  be  felt  with  every  action  of  the  syringe, 
an  impulse  or  beat,  which  corresponds  exactly  with  what  we  feel  in  the 
arteries  of  the  living  body  witii  every  contraction  of  the  heart,  and  call 
the  pulse.  Thv.  ])ulse  is  essentially  caused  by  an  expansion  ware,  wliich 
is  due  to  the  injection  of  blood  into  an  already  full  aorta:  which  blood 


CIRCULATION  OF  THE  BLOOD. 


143 


expanding  the  vessel  produces  the  pulse  in  it,  almost  coincidently  with 
the  systole  of  the  left  ventricle.  As  the  force  of  the  left  ventricle,  however, 
is  not  expended  in  dilating  the  aorta  only,  the  wave  of  blood  jjasses  on, 
expanding  the  arteries  as  it  goes,  running  as  it  were  on  the  surface  of  the 
more  slowly  traveling  blood  already  contained  in  them,  and  producing  the 
pulse  as  it  proceeds. 

The  distension  of  each  artery  increases  both  its  length  and  its  diameter. 
In  their  elongation,  the  arteries  change  their  form,  the  straight  ones  be- 
coming slightly  curved,  and  those  already  curved  becoming  more  so,  but 
they  recover  their  previous  form  as  well  as  their  diameter  when  the  ven- 
tricular contraction  ceases,  and  their  elastic  walls  recoil.  The  increase  of 
their  curves  which  accompanies  the  distension  of  arteries,  and  the  succeed- 
ing recoil,  may  be  well  seen  in  the  prominent  temporal  artery  of  an  old 
person.  In  feeling  the  pulse,  the  finger  cannot  distinguish  the  sensation 
produced  by  the  dilatation  from  that  produced  by  the  elongation  and 


BUTTON 


Fig.  124.— Diagram  of  the  mode  of  action  of  the  Sphygmograph, 

curving;  that  which  it  perceives  most  plainly,  however,  is  the  dilatation, 
or  return,  more  or  less,  to  the  cylindrical  form,  of  the  artery  which  has 
been  partially  flattened  by  the  finger. 

The  pulse — due  to  any  given  beat  of  the  heart — is  not  perceptible  at 
the  same  moment  in  all  the  arteries  of  the  body.  Thus, — it  can  be  felt 
in  the  carotid  a  very  short  time  before  it  is  perceptible  in  the  radial  artery, 
and  in  this  vessel  again  before  the  dorsal  artery  of  the  foot.  The  delay 
in  the  beat  is  in  proportion  to  the  distance  of  the  artery  from  the  heart, 
but  the  difference  in  time  between  the  beat  of  any  two  arteries  never 
exceeds  probably  ^  to  -J^  of  a  second. 

A  distinction  must  be  carefully  made  between  the  passage  of  the  loave 
along  the  arteries  and  the  velocity  of  the  stream  (p.  165)  of  blood.  Both 
wave  and  current  are  present;  but  the  rates  at  which  they  trawl  are  very 
different;  that  of  the  wave  16*5  to  33  feet  per  second  (5  to  10  metres) 
being  twenty  or  thirty  times  as  great  as  that  of  the  current. 

The  Sphygmograph. — A  great  deal  of  light  has  been  thrown  on 
what  may  be  called  the  form  of  the  pulse  by  the  sphygmograph  (Figs. 
124  and  125).    The  principle  oi]  which  the  sphygmograph  acts  is  very 


lU 


HAND-BOOK  OF  PHYSIOLOGY. 


simple  (see  Fig.  124).  The  small  button  replaces  the  finger  in  the  act  of 
taking  the  pulse^,  and  is  made  to  rest  lightly  on  the  artery,  the  pulsations 
of  which  it  is  desired  to  investigate.  The  up-and-down  movement  of  the 
button  is  communicated  to  the  lever,  to  the  hinder  end  of  which  is  at- 
tached a  slight  spring,  which  allows  the  lever  to  move  up,  at  the  same 
time  that  it  is  just  strong  enough  to  resist  its  making  any  sudden  jerk. 


Fig.  125.— The  Sphygmograph  applied  to  the  arm. 

and  in  the  interval  of  the  beats  also  to  assist  in  bringing  it  back  to  its 
original  position.  For  ordinary  purposes  the  instrument  is  bound  on  the 
wrist  (Fig.  125). 

It  is  evident  that  the  beating  of  the  pulse  with  the  reaction  of  the 
spring  will  cause  an  up-and-down  movement  of  the  lever,  the  pen  of  which 
will  write  the  effect  on  a  smoked  card,  which  is  made  to  move  by  clock- 
work in  the  direction  of  the  arrow.  Thus  a  tracing  of  the  pulse  is  ob- 
tained, and  in  this  way  much  more  delicate  effects  can  be  seen,  than  can 
be  felt  on  the  application  of  the  finger. 

The  pulse-tracing  differs  somewhat  according  to  the  artery  upon  which 
the  sphygmograph  is  applied,  but  its  general  characters  are  much  the 
same  in  all  cases.    It  consists  of: — A  sudden  upstroke  (Fig.  126,  a),  which 

is  somewhat  higher  and  more  abrupt  in 
the  pulse  of  the  carotid  and  of  other 
arteries  near  the  heart  than  in  the  radial 
and  other  arteries  more  remote;  and  a 
gradual  decline  (b),  less  abrupt,  and 
therefore  taking  a  longer  time  than  (a). 
It  is  seldom,  however,  that  the  decline  is 
an  uninterrupted  fall:  it  is  usually  marked 
about  half-way  by  a  distinct  notch  (c), 

Fig.  VSk-  Diagram  of  pulse  tracing.  called  the  dlCrottC  notch,  whicll  is  caUSCd 
A.  upstroke;  b,  down-stroke;  c,  predi-  ^     i  l 

erotic  wave;  D,  dicrotic;  E,  post  dicrotic  by  a  sccoud  morc  or  loss  markoa  ascent 
^*^^*  of  the  lever  at  that  point  by  a  second  wave 

called  the  dicrotic  wave  (d);  not  unfrequently  (in  which  case  the  tracing 
is  said  to  liave  a  double  apex)  there  is  also  soon  after  the  commencement 
of  the  descent  a  sliglit  ascent  previous  to  the  dicrotic  notcli,  this  is  called 
the  predicrotic  wave  (c),  and  in  addition  there  may  be  one  or  more 
slight  ascents  after  the  dicrotic,  coModpost  dicrotic  (e). 


CIllCULATION  OF  THE  liJ.OOD. 


145 


TlLe  explanation  of  these  tracings  presents  some  difficulties,  not,  how- 
ever, as  regards  tlie  two  primary  factors,  viz.,  the  upstroke  and  down- 
stroke,  because  they  are  universally  taken  to  mean  the  sudden  injection 
of  blood  into  the  already  full  arteries,  and  that  this  passes  through  the 
artery  as  a  wave  and  expands  them,  the  gradual  fall  of  the  lever  signify- 
ing the  recovery  of  the  arteries  by  their  recoil.  It  may  be  demonstrated 
on  a  system  of  elastic  tubes,  such  as  was  described  above,  where  a  syringe 
pumps  in  water  at  regular  intervals,  just  as  well  as  on  the  radial  artery, 
or  on  a  more  complicated  system  of  tubes  in  which  the  heart,  the  arteries, 
the  capillaries  and  veins  are  represented,  which  is  known  as  an  arterial 
schema.  If  we  place  two  or  more  sphygmographs  upon  such  a  system 
of  tubes  at  increasing  distances  from  the  pump,  we  may  demonstrate 


Fig.  127.— Diagram  of  the  formation  of  the  pulse-tracing.  A,  percussion  wave;  B,  tidal  ware; 
C,  dicrotic  wave.  (Mahomed.) 

that  the  rise  of  the  lever  commences  first  in  that  nearest  the  pump, 
and  is  higher  and  more  sudden,  while  at  a  longer  distance  from  the  pump 
the  wave  is  less  marked,  and  a  little  later.  So  in  the  arteries  of  the  body 
the  wave  of  blood  gradually  gets  less  and  less  as  we  approach  the  periphery 
of  the  arterial  system,  and  is  lost  in  the  capillaries.  By  the  sudden  in- 
jection of  blood  two  distinct  waves  are  produced,  which  are  called  the 
tidal  and  percussion  waves.  The  tidal  wave  occurs  whenever  fluid  is 
injected  into  an  elastic  tube  (Fig.  127,  b),  and  is  due  to  the  expansion  of 
the  tube  and  its  more  gradual  collapse.  The  percussion  wave  occurs 
(Fig.  127,  a)  when  the  impulse  imparted  to  the  fluid  is  more  sudden; 
this  causes  an  abrupt  upstroke  of  the  lever,  which  then  falls  until  it  is 
again  caught  up  perhaps  by  the  tidal  wave  which  begins  at  the  same  time 
but  is  not  so  quick. 
Vol.  I.— 10. 


146 


HAND-BOOK  OF  PHYSIOLOGY. 


In  this  way,  generally  speaking,  the  apex  of  the  upstroke  is  double, 
the  second  upstroke,  the  so-called  predicrotic  elevation  of  the  lever, 
representing  the  tidal  wave.  The  double  apex  is  most  marked  in  tracings 
from  large  arteries,  especially  when  their  tone  is  deficient.    In  tracings. 


Fig.  128,— Pulse-tracing  of  radial  artery,  somewhat  deficient  in  tone.  (Sanderson.) 

on  the  other  hand,  from  arteries  of  medium  size,  e.g.,  the  radial,  the 
upstroke  is  usually  single.  In  this  case  the  percussion-impulse  is  not 
sufficiently  strong  to  jerk  up  the  lever  and  produce  an  effect  distinct 
from  that  of  the  systolic  wave  which  immediately  follows  it,  and  which 


Fig.  129.— Pulse-tracing  of  radial  artery,  with  double  apex.  (Sanderson.) 


continues  and  completes  the  distension.  In  cases  of  feeble  arterial  ten- 
sion, however,  the  percussion-impulse  may  be  traced  by  the  spliygmo- 
graph,  not  only  in  the  carotid  pulse,  but  to  a  less  extent  in  the  radial  also 
(Fig.  129). 

The  interruptions  in  the  downstroke  are  called  the  hatacrotic  waves, 
to  distinguish  them  from  an  interruption  in  the  upstroke,  called  the  an- 
acrotic wave,  which  is  occasionally  met  with  in  cases  in  which  the  predi- 
crotic or  tidal  wave  is  higher  than  the  percussion  wave. 


K 

A  -A 

■\  ! 

Fig.  130.— Anacrotic  pulse  from  a  case  of  aortic  aneurism.  A,  anacrotic  wave  (or  percussion 
wave).   B,  tidal  or  predicrotic  wave,  continued  rise  in  tension  (or  higher  tidal  wave). 

There  is  considerable  difference  of  opinion  as  to  Avhether  the  dicrotic 
wave  is  present  in  health  generally,  and  also  as  to  its  cause.  The  balance 
of  opinion  ap[)ears  to  be  in  favor  of  the  belief  of  its  presence  in  health, 
although  it  may  be  very  faint;  while,  at  any  rate,  in  certain  conditions 
not  necessarily  diseased,  it  becomes  so  marked  as  to  be  quite  plain  to  the 
unaided  finger.  Such  a  ])ulse  is  called  dirrotic.  Sometimes  the  dicrotic  rise 
exceeds  the  iiiitiid  u])stn)la',  and  the  ])ulso  is  ihen  called  hypordicroiic. 

As  to  the  cause  of  d icroi  isui,  o\w  oj-inion  is  lliat  it,  is  duo  to  a  nn'overv 


CIRCULATION  OF  THE  BLOOD. 


147 


of  pressure  during  the  elastic  recoil,  in  consequence  of  a  rebound  from 
the  periphery,  and  it  may  indeed  be  produced  on  a  schema  by  obstructing 
the  tube  at  a  little  distance  beyond  the  spot  where  the  sphygmograph 
is  placed.  Against  this  view,  however,  is  the  fact  that  the  notch 
appears  at  about  the  same  point  in  the 
downstroke  in  tracings  from  the  carotid 
and  from  the  radial,  and  not  first  in 
the  radial  tracing,  as  it  should  do,  since 
that  artery  is  nearer  the  periphery  than 
the  carotid,  and  as  it  does  in  the  cor- 
responding experiment  with  the  arterial 
schema  when  the  tube  is  obstructed. 
The  generally  accepted  notion  among 
clinical  observers,  is  that  the  dicrotic 
wave  is  due  to  the  rebound  from  the 
aortic  valves  causing  a  second  wave;  but 
the  question  cannot  be  considered  set- 
tled, and  the  presence  of  marked  dicro- 
tism  in  cases  of  haemorrhage,  of  anaemia, 
and  of  other  weakening  conditions,  as 
well  as  its  presence  in  cases  of  dimin- 
ished pressure  within  the  arteries,  woiild 
imply  that  it  might,  at  any  rate  some- 
times, be  due  to  the  altered  specific 
gravity  of  the  blood  within  the  vessels, 
either  directly  or  through  the  indirect 
effect  of  these  conditions  on  the  tone 
of  the  arterial  walls.  Waves  may  be 
produced  in  any  elastic  tube  when  a 
fluid  is  being  driven  through  it  with  an 
intermittent  force,  such  waves  being 
called  luaves  of  oscillation  (M.  Eoster). 
They  have  received  various  explana- 
tions. In  an  arterial  schema  they  vary 
Tvith  the  specific  gravity  of  the  fluid 
used,  and  with  the  kind  of  tubing,  and  may  be  therefore  supposed  to 
vary  in  the  body  with  the  condition  of  the  blood  and  of  the  arteries. 

Some  consider  the  secondary  waves  in  the  downstroke  of  a  normal 
wave  to  be  due  to  oscillation;  but,  as  just  mentioned,  even  if  this  be  the 
case,  as  is  most  likely,  with  post-dicrotic  waves,  the  dicrotic  wave  itself  is 
almost  certainly  due  to  the  rebound  from  the  aortic  valves. 

The  anacrotic  notch  is  usually  associated  with  disease  of  the  arteries, 
e.g.,  in  atheroma  and  aneurism.  The  dicrotic  notch  is  called  diastolic  or 
aortic,  and  indicates  closure  of  the  aortic  valves. 


Fig.  131. — Diagrams  of  pulse  curves  with 
exaggeration  of  one  or  other  of  the  three 
waves.  A.  percussion;  B,  tidal:  C.  dicrotic. 
1,  percussion  wave  very  marked;  2,  tidal 
wave  sudden;  3.  dicrotic  pulse  curve;  4  and 
5,  the  tidal  wave  very  exaggerated,  from 
high  tension.  (Mahomed.) 


148 


HAND-BOOK  OF  PHYSIOLOGY. 


Of  the  three  main  parts  then  of  a  pulse-tracing,  viz.,  the  percussion 
wave,  the  tidal,  and  the  dicrotic,  the  percussion  wave  is  produced  by 
sudden  and  forcible  contraction  of  the  heart,  perhaps  exaggerated  by  an 
excited  action,  and  may  be  transmitted  much  more  rapidly  than  the  tidal 
wave,  and  so  the  tAvo  may  be  distinct;  frequently,  however,  they  are  in- 
separable. The  dicrotic  wave  may  be  as  great  or  greater  than  the  other 
two. 

According  to  Mahomed,  the  distinctness  of  the  three  waves  depends 
upon  the  following  conditions: — 

The 2^ercussio?i  wave  is  increased  by: — 1.  Forcible  contraction  of  the 
Heart;  2.  Sudden  contraction  of  the  Heart;  3.  Large  volume  of  blood; 
4.  Fulness  of  vessel;  and  diminished  by  the  reversed  conditions. 

The  tided  wave  is  increased  by: — 1.  Slow  and  prolonged  contraction 
of  the  Heart;  2.  Large  volume  of  blood;  3.  Comparative  emptiness  of 
vessels;  4.  Diminished  outflow  or  slow  capillary  circu- 
lation; and  diminished  by  the  reversed  conditions. 

The  dicrotic  wave  is  increased  by: — 1.  Sudden  con- 
traction of  the  Heart;  2.  Comparative  emptiness  of 
vessels;  3.  Increased  outflow  or  rapid  capillary  circu- 
lation; 4.  Elasticity  of  the  aorta;  5.  Eelaxation  of  mus- 
cular coat;  and  diminished  by  the  reversed  conditions. 

One  very  important  precaution  in  the  use  of  the 
sphygmograph  lies  in  the  careful  regulation  of  the  pres- 
sure. If  the  pressure  be  too  great,  the  characters  of  the 
pulse  may  be  almost  entirely  obscured,  or  the  artery  may 
be  entirely  obstructed,  and  no  tracing  is  obtained;  and 
on  the  other  hand,  if  the  pressure  be  too  slight,  a  very 
small  part  of  the  characters  may  be  represented  on  the 
tracing. 

The  Pkessure  of  the  Blood  within  the  Arteeies 

(PRODUCIKG  arterial  TEXSIOJs). 

It  will  be  understood  from  the  foregoing  that  the 
arteries  in  a  normal  condition,  are  continually  on  the 
of  mereuSarmLSl?^-  strctcli  during  life,  and  in  consequence  of  the  injection 
of  more  blood  at  each  systole  of  the  venti-icle  into  the 
elastic  aorta,  this  stretched  condition  is  exaggerated  each  time  the  ventricle 
empties  itself.  This  condition  of  the  arteries  js  due  to  the  pressure  of 
blood  within  them,  because  of  the  resistance  presented  by  the  smaller  ar- 
teries and  capillaries  (i)eriphcral  resistance)  to  the  emptying  of  the  arterial 
system  in  the  intervals  betwcMMi  the  contractions  of  tlu^  ventricle,  and  is 
called  tlie  condition  of  arlcrial  tension.  On  the  otlier  hand,  it  must  be 
equally  clear  thai,  as  the  blood  is  forcibly  injected  into  the  already  full 


CIRCULATION  OF  THE  liLOOD. 


141) 


arteries  against  their  elasticity,  it  must  be  subjected  to  the  pressure  of 
the  arterial  walls,  the  elastic  recoil  sending  on  the  blood  after  the  imme- 
diate effect  of  the  systole  has  passed;  so  that,  when  an  artery  is  cut  across, 
the  blood  is  projected  forward  by  this  force  for  a  considerable  distance; 
at  each  ventricular  systole,  a  jet  of  blood  escaping,  although  the  stream 
does  not  cease  flowing  during  the  diastole. 

The  relations  which  exist  between  the  arteries  and  their  contained 
blood  are  obviously  of  the  utmost  importance  to  the  carrying  on  of  the 
circulation,  and  it  therefore  becomes  necessary  to  be  able  to  gauge  the 


Fig.  133.— Diagram  of  mercurial  kymograph,  a,  revolving  cylinder,  worked  by  a  clockwork  ar- 
rangement contained  in  the  box  (b),  the  speed  being  regulated  by  a  fan  above  the  box;  cylinder  sup- 
ported by  an  upright  (6),  and  capable  of  being  raised  or  lowered  by  a  screw  (a),  by  a  handle  attached 
to  it;  D,  c,  E,  represent  mercm-ial  manometer,  a  somewhat  different  form  of  which  is  shown  in  next 
figure. 

alterations  in  blood-pressure  very  accurately.  This  may  be  done  by 
means  of  a  mercurial  manometer  in  the  following  way: — The  short  hori- 
zontal limb  of  this  (Fig.  132,  1)  is  connected,  by  means  of  an  elastic  tube 
and  cannula,  with  the  interior  of  an  artery;  a  solution  of  sodium  or  po- 
tassium carbonate  being  previously  introduced  into  this  part  of  the  appa- 
ratus to  prevent  coagulation  of  the  blood.  The  blood-pressure  is  thus 
communicated  to  the  upper  part  of  the  mercurial  column  (2);  and  the 
depth  to  which  the  latter  sinks,  added  to  the  height  to  which  it  rises  in 
the  other  (3),  will  give  the  height  of  the  mercurial  column  which  the 


150 


HAND-BOOK  OF  PHYSIOLOGY. 


blood-pressure  balances;  the  weight  of  the  soda  solution  being  sub- 
tracted. 

For  the  estimation  of  the  arterial  tension  at  any  given  moment,  no 
further  apparatus  than  this,  which  is  called  Poiseuille^s  hcBmadynamometer, 
is  necessary;  but  for  noting  the  variatioiis  of  pressure  in  the  arterial  sys- 
tem, as  well  as  its  absolute  amount,  the  instrument  is  usually  combined 

with  a  registering  apparatus  and  in  this  form  is 
called  a  kymogrcqih. 

The  kymograph,  invented  by  Ludwig,  is 
composed  of  a  hsemadynamometer,  the  open 
mercurial  column  of  which  supports  a  floating 
piston  and  vertical  rod,  with  short  horizontal 
pen  (Fig.  134).  The  pen  is  adjusted  in  con- 
tact with  a  sheet  of  paper,  which  is  caused  to 
move  at  a  uniform  rate  by  clockwork;  and 
thus  the  up-and-down  movements  of  the  mer- 
curial column,  which  are  communicated  to  the 
rod  and  pen,  are  marked  or  registered  on  the 
moving  paper,  as  in  the  registering  apparatus 
of  the  sphygmograph,  and  minute  variations 
cire  graphically  recorded  (Fig.  135). 

For  some  purposes  the  spring  kymograph  of 
Fick  (Fig.  136)  is  preferable  to  the  mercurial 
kymograph.  It  consists  of  a  hollow  C-shaped 
spring,  filled  with  fluid,  the  interior  of  wdiich 
is  brought  into  connection  with  the  interior 
of  an  artery,  by  means  of  a  flexible  metallic  tube  and  cannula.  In 
response  to  the  pressure  transmitted  to  its  interior,  the  spring,  c,  tends 
to  straighten  itself,  and  the  movement  thus  produced  is  communicated 
by  means  of  a  lever,  h,  to  a  writing-needle  and  registering  apparatus. 


Fig.  134. — Diagram  of  mercu- 
rial manometer,  a.  Floatiag  rod 
and  pen.  6.  Tube,  which  commu- 
nicates with  a  bottle  containing 
an  alkaline  solution,  c'.  Elastic 
tube  and  cannula,  the  latter  being 
Intended  for  insertion  in  an  artery. 


Fig.  135.— Normal  tracing  of  arterial  pressure  in  the  rabbit  obtained  with  the  mercurial  kymo- 
graph. The  smaller  undulations  correspond  with  the  heart  beats;  the'lai'ger  curves  with  the  respir- 
atory movements.  (Burdon-Sanderson.) 

Fig.  137  exhibits  an  ordinary  arterial  pulse-tracing,  as  obtained  by  the 
8pring-kymograi)h. 

From  obscrvnl ions  Avlii(^h  liavo  been  made  by  iucmiis  of  the  mercurial 
manometer,  it  has  been  found  that  tlie  })resRuro  of  l)h)0(l  in  the  carotici  of 
a  rabbit  is  capable  of  supporting  a  column  of  2  to  \)l  inches  (50  to  90 


CIRCULATION  OF  THE  BLOOD. 


151 


mm.)  of  mercury,  in  the  dog  4  to  7  inches  (100  to  175  mm.),  in  the 
horse  5  to  8  inches  (150  to  200  mm.),  and  in  man  about  the  same. 

To  measure  the  absolute  amount  of  this  pressure  in  any  artery,  it  is 
necessary  merely  to  multiply  the  area  of  its  transverse  section  by  the 
height  of  the  column  of  mercury  which  is  already  known  to  be  supported 
by  the  blood-pressure  in  any  part  of  the  arterial  system.  The  weight 
of  a  column  of  mercury  thus  found  will  represent  the  pressure  of  the 
blood.    Calculated  in  this  way,  the  blood-pressure  in  the  human  aorta  is 


Fig.  136,— a  form  of  Fick's  Spring  Kymograph,  a,  tube  to  be  connected  with  artery;  c,  hollow 
spring,  the  movement  of  which  moves  b,  the  writing  lever;  e,  screw  to  regulate  height  of  6;  d,  out- 
side protective  spring;     screw  to  fix  on  the  upright  of  the  support. 

equal  to  4  lb.  4  oz.  avoirdupois;  that  in  the  aorta  of  the  horse  being 
11  lb.  9  oz. ;  and  that  in  the  radial  artery  at  the  human  wrist  only  4  drs. 
Supposing  the  muscular  power  of  the  right  ventricle  to  be  only  one- 
half  that  of  the  left,  the  blood-pressure  in  the  pulmonary  artery  will  be 
only  2  lb.  2  oz.  avoirdupois.  The  amounts  above  stated  represent  the 
arterial  tension  at  the  time  of  the  ventricular  contraction. 

The  blood-pressure  is  greatest  in  the  left  ventricle  and  at  the  begin- 
ning of  the  aorta,  and  decreases  toward  the  capillaries.  It  is  greatest  in 
the  arteries  at  the  period  of  the  ventricular  systole,  and  is  least  in  the 
auricles,  during  diastole,  when  the  pressure  there  and  in  the  great  veins 
becomes,  as  we  have  seen,  negative.  The  mean  arterial  pressure  equals 
the  average  of  the  pressures  in  all  the  arteries.  The  pressure  in  the 
veins  is  never  more  than  one-tenth  of  the  pressure  in  the  corresponding 


152 


HAND-BOOK  OF  PHYSIOLOGY. 


arteries  and  is  greatest  at  the  time  of  auricular  systole.  There  is  no  peri- 
odic variation  in  venous  pressure,  as  there  is  in  the  arterial,  except  in 
the  great  veins. 


Fig.  137.— Normal  arterial  tracing  obtained  vrith  Fick"s  kymograph  in  the  dog.  (Burdon- 
Sanderson.) 

Variations  of  Blood  Pressure. — Many  circumstances  cause  con- 
siderable variations  in  the  amount  of  the  blood-pressure.  The  following 
are  the  chief: — (1)  Changes  in  tJie  beat  of  the  Heart;  (2)  Changes  in  the 
Arteries  and  Capillaries;  (3)  Changes  due  to  Nerve  Action;  (4)  Clianges 
in  the  Blood;  (5)  Respiratory  Changes. 

1.  Changes  in  the  Beat  of  the  Heart. — The  systole  and  diastole  of  the 
muscular  chambers.  The  arterial  tension  increases  during  systole  and 
diminishes  during  diastole.  The  greater  the  frequency,  moreover^  of  the 
heart's  contractions,  the  greater  is  the  blood- j)ressure,  cceteris  paribus; 
although  this  effect  is  not  constant,  as  it  may  be  compensated  for  by  the 
delivery  into  the  arteries  at  each  beat  of  a  comparatively  small  quantity 
of  blood.  The  greater  the  quantity  of  blood  expelled  from  the  heart  at 
each  contraction  the  greater  is  the  blood-pressure. 

The  quantity  and  quality  of  the  blood  nourishing  the  heart's  substance 
through  the  coronary  arteries  must  exercise  also  a  very  considerable 
influence  upon  its  action,  and  therefore  upon  the  blood-pressure. 

2.  Changes  in  the  Arteries  and  Capillaries. — Variations  in  the  degree 
of  contraction  of  the  smaller  arteries  modify  the  blood-pressure  by  favor- 
ing or  impeding  the  accumulation  of  blood  in  the  arterial  system  which 
follows  every  contraction  of  the  heart;  the  contraction  of  the  arterial 
walls  increasing  the  blood-pressure,  while  their  relaxation  lowers  it. 

3.  Changes  due  to  Nerve  Action. — As  with  the  heart,  so  with  the 
blood-vessels,  the  action  of  the  nervous  system  is  very  important  in  rela- 
tion to  the  blood-pressure;  regulating,  as  it  does,  not  only  the  force,  fre- 
quency, and  length  of  the  heart's  systole,  but  also  the  condition  of  the 
arteries,  both  through  the  central  and  ])eripheral  vaso-motor  centres.  As 
this  subject  has  not  yet  been  fully  considered  it  will  be  as  well  to  treat  of 
it  liere. 

It  is  upon  the  muscular  coat  of  the  arteries  that  the  nervous  system 
exercises  its  infhience;  tlie  elastic  element  possessing,  as  must  be  obvious, 
rather  physical  than  vital  properties.  Tlie  muscular  tissue  in  the  walls 
of  (lie  vessels  increases  relatively  to  the  other  coats  as  the  arteries  grow 
smaller,  so  that  in  the  smallest  arteries  it  is  develo])ed  out  of  all  propor- 


CIRCULATION  OF  THE  P>LOOJ). 


tion  to  the  other  elements;  in  fact,  in  passing  from  cai)illary  vessels,  made 
up  as  we  have  seen  of  endothelial  cells  with  a  ground  substance,  the  first 
change  which  occurs  as  the  vessels  become  larger  (on  the  side  of  the 
arteries)  is  the  appearance  of  muscular  fibres.  Thus  the  nervous  system 
is  more  powerful  in  regulating  the  calibre  of  the  smaller  than  of  the  larger 
arteries. 

It  has  been  shown  that  if  the  cervical  sympathetic  nerve  be  divided  in 
a  rabbit,  the  blood-vessels  of  the  corresponding  side  become  dilated.  The 
effect  is  best  seen  in  the  ear,  which  if  held  up  to  the  light  is  seen  to 
become  redder,  and  the  arteries  to  become  larger.  The  whole  ear  is  dis- 
tinctly warmer  than  the  opposite  one.  This  effect  is  produced  by  remov- 
ing the  arteries  from  the  influence  of  the  central  nervous  system,  which 


Fig.  138.— Plethysmograph.  By  means  of  this  apparatus,  the  alteration  in  volume  of  the  arm. 
E,  which  is  enclosed  in  a  glass  tube,  a,  fiUed  with  fluid,  the  opening  through  which  it  passes  being 
firmly  closed  by  a  thick  gutta  percha  band,  f,  is  communicated  to  the  lever,  d,  and  registered  by  a 
recording  apparatus.  The  fluid  in  a  communicates  with  that  in  b,  the  upper  limit  of  which  is  above 
that  in  a.  The  chief  alterations  in  volume  are  due  to  alteration  in  the  blood  contained  in  the  arm. 
When  the  volume  is  increased,  fluid  passes  out  of  the  glass  cyhnder,  and  the  lever,  d,  also  is  raised, 
and  when  a  decrease  takes  place  the  fluid  returns  again  from  b  to  a.  It  will  therefore  be  evident 
that  the  apparatus  is  capable  of  recording  alterations  of  blood-pressure  in  the  arm.  Apparatus 
founded  upon  the  same  principle  have  been  used  for  recording  alterations  in  the  volume  of  the  spleen 
ai.d  kidney. 

influence  usually  passes  down  the  divided  nerve;  for  if  the  peripheral  end 
of  the  divided  nerve  {i.e.,  that  farthest  from  the  brain)  be  stimulated, 
the  arteries  which  were  before  dilated  return  to  their  natural  size,  and 
the  parts  regain  their  primitive  condition.  And,  besides  this,  if  the 
stimulus  which  is  applied  be  too  strong  or  too  long  continued,  the  point 
of  normal  constriction  is  passed,  and  the  vessels  become  much  more  con- 
tracted than  normal.  The  natural  condition,  which  is  somewhere  about 
midway  between  extreme  contraction  and  extreme  dilatation,  is  called  the 
natural  tone  of  an  artery,  and  if  this  be  not  maintained,  the  vessel  is  said 
to  have  lost  tone,  or  if  it  be  exaggerated,  the  tone  is  said  to  be  too  great. 
The  influence  of  the  nervous  system  upon  the  vessels  consists  in  maintain- 
ing a  natural  tone.  The  effects  described  as  having  been  produced  by 
section  of  the  cervical  sympathetic  and  by  subsequent  stimulation  are  not 
peculiar  to  that  nerve,  as  it  has  been  found  that  for  every  j)art  of  the 


154 


HAND-BOOK  OF  PHYSIOLOGY. 


body  tliere  exists  a  nerve  the  division  of  which  produces  the  same  effects, 
viz.,  dilatation  of  the  arteries;  such  may  be  cited  as  the  case  with  the 
sciatic,  the  splanchnic  nerves,  and  the  nerves  of  the  brachial  plexus: 
when  divided,  dilatation  of  the  blood-vessels  in  the  parts  supplied  by 
them  taking  place.  It  appears,  therefore,  that  nerves  exist  which  have  a 
distinct  control  over  the  vascular  supply  of  a  part. 

These  nerves  are  called  vaso-motor;  or,  since  they  seem  to  run  now 
in  cerebro-spinal  nerves,  now  in  the  sympathetic,  we  speak  of  those 
nerves  as  containing  vaso-motor  fibres,  in  addition  to  the  fibres  which 
have  other  functions. 

Vaso-motor  centres. — Experiments  by  Ludwig  and  others  show 
that  the  vaso-motor  fibres  come  primarily  from  grey  matter  (vaso-motor 
centre)  in  the  interior  of  the  medulla  oblongata,  between  the  calamus 
scriptorius  and  the  corpora  quadrigemina.  Thence  the  vaso-motor  fibres 
pass  down  in  the  interior  of  the  spinal  cord,  and  issuing  with  the  anterior 
roots  of  the  spinal  nerves,  traverse  the  various  ganglia  on  the  pra3 -vertebral 
cord  of  the  sympathetic,  and,  accompanied  by  branches  from  these 
ganglia,  pass  to  their  destination. 

Secondary  or  subordinate  centres  exist  in  the  spinal  cord,  and  local 
centres  in  various  regions  of  the  body,  and  through  these,  directly  under 
ordinary  circumstances,  vaso-motor  changes  are  also  effected. 

The  influence  exerted  by  the  chief  vaso-motor  centre  is  called  into 
play  in  several  ways,  but  chiefly  by  afferent  ^sensory)  stimuli,  and  it  may 
be  exerted  in  two  ways,  either  to  increase  its  usual  action  which  main- 
tains a  medium  tone  of  the  arteries  or  to  diminish  such  action.  This 
afferent  influence  upon  the  centre  may  be  extremely  well  shown  by  the 
action  of  a  nerve  the  existence  of  which  was  demonstrated  by  Cyon  and 
Ludwig,  and  which  is  called  the  depressor,  because  of  its  characteristic 
influence  on  the  blood-pressare. 

Depressor  Xerve. — This  small  nerve  arises,  in  the  rabbit,  from  the 
superior  laryngeal  branch,  or  from  this  and  the  trunk  of  the  pneumogas- 
tric  nerve,  and  after  communicating  with  filaments  of  the  inferior  cervical 
ganglion  proceeds  to  the  heart. 

If  during  an  observation  of  the  blood-pressure  of  a  rabbit  this  nerve 
be  divided,  and  the  central  end  (i.e.,  that  nearest  the  brain)  be  stimu- 
lated, a  remarkable  fall  of  blood-jn-essure  ensues  (Fig.  130). 

Tlie  cause  of  the  fall  of  blood-pressure  is  found  to  proceed  from  the 
dilatation  of  the  vascular  district  supplied  by  tlie  splanchnic  nerves,  in 
consequence  of  wliich  it;  holds  a  mucli  larger  quantity  of  blood  than  usual, 
and  tliis  very  greatly  diminislios  the  blood  in  the  vessels  elsewhere,  and 
so  materially  affects  the  blood-})r(*8Sure.  This  effect  of  the  depressor  nerve 
is  presumed  to  prove  that  the  nerve  is  a  means  of  conveying  to  the  vaso- 
motor centre  indications  of  such  conditions  of  the  heart  as  require  a 
diminution  of  the  tension  in  the  blood-vessels;  us,  for  exam})le,  when  the 


CIRCULATION   OV  THE  BLOOD. 


155 


heart  cannot,  with  siilliciont  ease,  proi)el  blood  into  the  ah'eacly  too  full  or 
too  tense  arteries. 

The  action  of  the  depressor  nerve  illustrates  the  effect  of  afferent  im- 
pulses in  causing  an  inhibition  of  the  vaso-motor  centre  as  regards  its 
action  upon  certain  -arteries.  There  exist  other  nerves,  however,  the 
stimulation  of  the  central  end  of  which  causes  a  Teverse  action  of  the 
centre,  or,  in  other  words,  increases  its  tonic  influence,  and  by  causing 


Fig.  139. — Tracing  showing  the  effect  on  blood  pressure  of  stimulating  the  central  end  of  the  De- 
pressor nerve  in  the  rabbit.  To  be  read  from  right  to  left.  T,  indicates  the  rate  at  which  the  re- 
cording-surf ace  was  traveling,  the  intervals  correspond  to  seconds :  C,  the  moment  of  entrance  of 
current;  O,  moment  at  which  it  was  shut  off.  The  effect  is  some  time  in  developing  and  lasts  after 
the  current  has  been  taken  off.  The  larger  undulations  are  the  respiratory  nerves;  the  pulse  oscilla- 
tions are  very  small.   (M.  Foster.) 

considerable  constriction  of  certain  arterioles,  either  locally  or  generally, 
increases  the  blood-pressure.  Moreover,  the  effect  of  stimulating  an 
afferent  nerve  may  be  to  dilate  or  constrict  the  arteries  either  generally 
or  in  the  part  supplied  by  the  afferent  nerve;  and  it  is  said  that  stimula- 
tion of  an  afferent  nerve  may  produce  a  kind  of  paradoxical  effect,  causing 
general  vascular  constriction  and  so  general  increase  of  blood-j)ressure  but 
at  the  same  time  local  dilatation.  This  must  evidently  have  an  immense 
influence  in  increasing  the  flow  of  blood  through  a  part. 

Not  only  may  the  vaso-motor  centre  be  reflexly  affected,  but  it  may 
also  be  affected  by  impulses  proceeding  to  it  from  the  cerebrum,  as  in 'the 
case  of  blushing  from  mind  disturbance,  or  of  pallor  from  sudden  fear. 
It  will  be  shown,  too,  in  the  chapter  on  Eespiration  that  the  circulation 
of  deoxygenated  blood  may  directly  stimulate  the  centre  itself. 

Local  Tonic  Centres. — Although  the  tone  of  the  arteries  is  influ- 
enced by  the  centres  in  the  cerebro-spinal  axis,  certain  experiments  point 
out  that  this  is  not  the  only  way  in  which  it  may  be  affected.  Thus  the 
dilatation  which  occurs  after  section  of  the  cervical  sympathetic  in  the 
first  experiment  cited  above,  only  remains  for  a  short  time,  and  is  soon 
followed — although  a  portion  of  the  nerve  may  have  been  removed 
entirely — by  the  vessels  regaining  their  ordinary  calibre;  and  afterward 


156 


HAND-BOOK  OF  PHYSIOLOGY. 


local  stimulation,  e.g.,  the  application  of  lieat  or  cold,  will  cause  dilatation 
or  constriction.  From  this  it  is  probable  that  there  exists  a  local 
mechanism  distinct  for  each  vascular  area,  and  that  the  effect  produced 
by  the  central  nervous  s}- stem  acts  through  it  much  in  the  same  way  as  the 
cardio-inhibitory  centre  in  the  medulla  acts  upon  the  heart  through  the 
ganglia  contained  within  its  muscular  substance. 

Central  impulses  may  inhibit  or  increase  the  action  of  these  local 
centres,  which  may  be  considered  to  be  sufficient  under  ordinary  circum- 
stances to  maintain  the  local  tone  of  the  vessels.  The  observations  upon 
the  functions  of  the  vaso-motor  nerves  appear  to  divide  them  into  four 
classes:  (1)  those  on  division  of  which  dilatation  occurs  for  some  time, 
and  which  on  stimulation  of  their  peripheral  end  produce  constriction; 
(2)  those  on  division  of  which  momentary  dilatation  followed  by  constric- 
tion occurs,  with  dilatation  on  stimulation;  (3)  those  on  division  of  which 
dilatation  is  caused,  which  lasts  for  a  limited  time,  with  constriction  if 
stimulated  at  once,  but  dilatation  if  some  time  is  allowed  to  elapse  before 
the  stimulation  is  applied;  (4)  a  class,  division  of  which  produces  no 
effect  but  which,  on  stimulation,  cause  according  to  their  function  either 
dilatation  or  constriction.  A  good  examj^le  of  this  fourth  class  is  afforded 
by  the  nerves  supplying  the  submaxillary  gland,  viz.,  the  chorda  tympani 
and  the  sympathetic.  When  either  of  these  nerves  is  simply  divided, 
no  change  takes  place  in  the  vessels  of  the  gland;  but  on  stimulating  the 
chorda  tympani  the  vessels  dilate,  and,  on  the  other  hand,  when  the 
sympathetic  is  stimulated  the  vessels  contract.  The  nerves  acting  like 
the  chorda  tympani  in  this  case  are  called  vaso-dUators,  and  those  like 
the  sympathetic  vaso-consfrictors.  The  third  class,  which  produce  at  one 
time  dilatation,  at  another  time  constriction,  are  believed  to  contain  both 
kinds  of  vaso-motor  nerve-fibres,  or  to  act  as  dilators  or  contractors 
according  to  the  condition  of  the  locaL  apparatus.  It  is  probable  that 
these  nerves  act  bv  inliibitino-  or  auo-mentinor  the  action  of  the  local  nerv- 

o  o  o 

ous  mechanism  already  referred  to;  and  as  they  are  in  connection  Avith 
the  central  nervous  system,  it  is  through  this  arrangement  that  that  sys- 
tem is  capable  of  influencing  or  of  maintaining  the  normal  local  tone. 

It  may  also  be  supposed  that  the  local  nerve-centres  themselves  may 
be  directly  affected  by  the  condition  of  blood  nourishing  them. 

'J'he  following  table  may  serve  as  a  summary  of  the  effect  of  the  nerv- 
ous system  upon  the  arteries  and  so  upon  tlie  blood-pressure: — 

A.  An  increase  of  the  blood-pressure  may  be  produced: — 

(1.)  \\y  st iiiuilnl ion  of  tlie  vaso-motor  centre  in  niodnlla,  either 
(v.  DirvrHii,  as  by  carbonated  oi*  deoxygenated  blood. 

liuUrccthi,  \)\  iin])ressi()ns  descending  from  the  cerebrum, 
rjj.,  in  sudiliMi  i):illor. 

licjh'A'Uj,  by  stimulation  of  sensory  nerves  anywhere. 


CIRCULATION  OF  THE  BLOOD. 


157 


(2.)  By  stimulation  of  the  centres  in  spinal  cord. 

Possibly  directly  or  indirectly,  certainly  reflexly. 
(3.)  By  stimulation  of  the  local  centres  for  each  vascular  area,  by 

the  vaso-constrictor  nerves,  or  directly  by  means  of  altered 

blood. 

B.  A  decrease  of  the  blood  pressure  may  be  produced: — 

(1.)  By  stimulation  of  the  vaso-motor  centre  in  medulla,  either 
(a.)  Directly,  as  by  oxygenated  or  aerated  blood. 
(fi.)  Indirectly,  by  impressions  descending  from  the  cerebrum 

— e.g.,  in  blushing. 
{y.)  Reflexly,  by  stimulation  of  the  depressor  nerve,  and 
consequent  dilatation  of  vessels  of  splanchnic  area,  and 
possibly  by  stimulation  of  other  sensory  nerves,  the  sen- 
sory impulse  being  interpreted  as  an  indication  for 
diminished  blood-pressure. 
(2.)  By  stimulation  of  the  centres  in  spinal  cord.  Possibly 

directly,  indirectly,  or  reflexly. 
(3.)  By  stimulation  of  local  centres  for  each  vascular  area  by  the 
vaso-dilator  nerve,  or  directly  by  means  of  altered  blood. 

4.  Changes  in  the  Mood. — a.  As  regards  quantity.  At  first  sight  it 
would  appear  that  one  of  the  easiest  ways  to  diminish  the  blood-pressure 
would  be  to  remove  blood  from  the  vessels  by  bleeding;  it  has  been  found 
by  experiment,  however,  that  although  the  blood-pressure  sinks  whilst 
large  abstractions  of  blood  are  taking  place,  as  soon  as  the  bleeding  ceases 
it  rises  rapidly,  and  speedily  becomes  normal;  that  is  to  say,  unless  so 
large  an  amount  of  blood  has  been  taken  as  to  be  positively  dangerous  to 
life,  abstraction  of  blood  has  little  effect  upon  the  blood-pressure.  The 
rapid  return  to  the  normal  pressure  is  due  not  so  much  to  the  withdraival 
of  lymph  and  other  fluids  from  the  body  into  the  blood,  as  was  formerly 
supposed,  as  to  the  regulation  of  the  peripheral  resistance  by  the  vaso- 
motor nerves;  in  other  words,  the  small  arteries  contract,  and  in  so  doing 
maintain  pressure  on  the  blood  and  favor  its  accumulation  in  the  arterial 
system.  This  is  due  to  th6  stimulation  of  the  vaso-motor  centre  from 
diminution  of  the  supply  of  blood,  and  therefore  of  oxygen.  The  failure 
of  the  blood-pressure  to  return  to  normal  in  the  too  great  abstraction 
must  be  taken  to  indicate  a  condition  of  exhaustion  of  the  centre,  and 
consequently  of  want  of  regulation  of  the  peripheral  resistance.  In  the 
same  way  it  might  be  thought  that  injection  of  blood  into  the  already 
pretty  full  vessels  would  be  at  once  followed  by  rise  in  the  blood-pressure, 
and  this  is  indeed  the  case  up  to  a  certain  point — the  pressure  does  rise, 
but  there  is  a  limit  to  the  rise.  Until  the  amount  of  blood  injected 
equals  about  2  to  3  per  cent,  of  the  body  weight  the  pressure  continues  to« 
rise  gradually;  but  if  the  amount  exceed  this  proportion,  the  rise  does  not 
continue.    In  this  case  therefore,  as  in  the  opposite  when  blood  is  ab- 


158 


HAND-BOOK  OF  PHYSIOLOG^Y. 


stracted,  the  vaso- motor  apparatus  must  counteract  the  great  increase  of 
pressure  by  dilating  tlie  small  vessels,  and  so  diminishing  the  peripheral 
resistance,  for  after  each  rise  there  is  a  partial  fall  of  pressure;  and  after 
the  limit  is  reached  the  whole  of  the  injected  blood  displaces,  as  it  were, 
an  equal  quantity  which  passes  into  the  small  veins,  and  remains  within 
them.  It  should  be  remembered  that  the  veins  are  capable  of  holding 
the  whole  of  the  blood  of  the  body. 

The  amount  of  blood  supplied  to  the  heart  both  to  its  substance  and 
to  its  chambers,  has  a  marked  effect  upon  the  blood-pressure. 

l.  As  regards  qucdity.  The  quality  of  the  blood  supplied  to  the  heart . 
has  a  distinct  effect  upon  its  contraction,  as  too  watery  or  too  little  oxy- 
genated blood  must  interfere  with  its  action.  Thus  it  appears  that  blood 
containing  certain  substances  affects  the  peripheral  resistance  by  acting 
upon  the  muscular  fibres  of  tlie  arterioles  themselves  or  upon  the  local 
centres,  and  so  altering  directly,  as  it  were,  the  calibre  of  the  vessels. 

5.  Resjyiratory  changes  affecting  the  blood-pressure  will  be  considered 
in  the  next  Chapter. 


OlRCULATIOlT  m  THE  CAPILLARIES. 


mm 


When  seen  in  any  transparent  part  of  a  living  adult  animal  by  means 
of  the  microscope  (Fig.  140)  the  blood  flows  with  a  constant  equable  mo- 
tion; the  red  blood-corpuscles  moving  along,  mostly  in  single  file,  and 
bending  in  various  ways  to  accommodate  themselves  to  the  tortuous  course 

of  the  capillary,  but  instantly  recovering  their 
normal  outline  on  reaching  a  wider  vessel. 

It  is  in  the  capillaries  that  the  chief  resist- 
ance is  offered  to  the  progress  of  the  blood; 
for  in  them  the  friction  of  the  blood  is  greatly 
increased  by  the  enormous  multiplication  of 
the  surface  with  which  it  is  brought  in  con- 
tact." 

At  the  circumference  of  the  stream  in  the 
larger  capillaries,  but  chiefly  in  the  small  arte- 
ries and  veins,  in  contact  with  the  walls  of 
the  vessel,  and  adhering  to  them,  there  is 
a  layer  of  liquor  sanguinis  which  appears  to 
be  motionless.  The  existence  of  this  ,*^^/7/  Jayer,  as  it  is  termed,  is 
inferred  both  from  tlie  general  fact  that  such  an  one  exists  in  all  fine 
tubes  traversed  by  fluid,  and  from  what  can  be  seen  in  watching  the  move- 
ments of  tlie  blood -corpuscles.  The  red  corpuscles  occupy  the  middle  of 
the  stroain  and  mow.  witli  comparative  rapidity;  the  colorless  lymph-cor- 
puscles run  inucli  nioi'c  slowly  by  the  walls  of  the  vessel;  while  next  to 
tho  Willi  tluM'c  is  often  a  transparent  S2)ace  in  whicli  the  fluid  appears  to 


Fia.  140.— Capillaries  (C)  in  the 
web  of  the  frop^'s  foot  connecting:  a 
small  artery  (A)  with  a  small  vein  V 
(after  Allen  Thomson). 


CIRCULATION  OF  THE  BLOOD. 


159 


be  at  rest;  for  if  any  of  tne  corpuscles  happen  to  be  forced  within  it,  they 
move  more  slowly  than  before,  rolling  lazily  along  the  side  of  the  vessel, 
and  often  adhering  to  its  wall.  Part  of  this  slow  movement  of  the  pale 
corpuscles  and  their  occasional  stoppage  may  be  due  to  their  having  a 
natural  tendency  to  adhere  to  the  walls  of  the  vessels.  Sometimes,  in- 
deed, when  the  motion  of  the  blood  is  not  strong,  many  of  the  white  cor- 
puscles collect  in  a  capillary  vessel,  and  for  a  time  entirely  prevent  the 
passage  of  the  red  corpuscles. 

Intermittent  flow  in  the  Capillaries. — When  the  peripheral  re- 
sistance is  greatly  diminished  by  the  dilatation  of  the  small  arteries  and 
capillaries,  so  much  blood  passes  on  from  the  arteries  into  the  capillaries 
at  each  stroke  of  the  heart,  that  there  is  not  sufficient  remaining  in  the 
arteries  to  distend  them,  ^hus,  the  intermittent  current  of  the  ventric- 
ular systole  is  not  converted  into  a  continuous  stream  by  the  elasticity 
of  the  arteries  before  the  capillaries  are  reached;  and  so  inter mittency  of 
the  flow  occurs  in  capillaries  and  veins  and  a  pulse  is  produced.  The 
same  phenomenon  may  occur  when  the  arteries  become  rigid  from  disease, 
and  when  the  beat  of  the  heart  is  so  slow  or  so  feeble 
that  the  blood  at  each  cardiac  systole  has  time  to  pass 
on  to  the  capillaries  before  the  next  stroke  occurs,  the 
amount  of  blood  sent  at  each  stroke  being  insufficient 
to  properly  distend  the  elastic  arteries. 

Diapedesis  of  Blood  Corpuscles. — Until  with- 
in the  last  few  years  it  has  been  generally  supposed 
that  the  occurrence  of  any  transudation  from  the  in- 
terior of  the  capillaries  into  the  midst  of  the  sur- 
rounding tissues  was  confined,  in  the  absence  of 
injury,  strictly  to  the  fluid  part  of  the  blood;  in  other 
words,  that  the  corpuscles  could  not  escape  from  the 
circulating  stream,  unless  the  wall  of  the  containing 
blood-vessel  were  ruptured.  It  is  true  that  an  Eng- 
lish physiologist,  Augustus  Waller,  affirmed,  in  1846, 
that  he  had  seen  blood-corpuscles,  both  red  and  white,  .  Fig.141.— a i^rge  cap- 
pass  bodily  through  the  wall  of  the  capillary  vessel    mesentery  eight  hours 

T-i.T  ,    '      1  /  ,^  r>      '  T,      after  irritation  had  been 

m  which  they  were  contamed  (thus  confirming  what  set  up,  showing  emigra- 
had  been  stated  a  short  time  previously  by  Addison);  Cells  in  the  act^of  trav- 
and  that,  as  no  opening  could  be  seen  before  their  wSi^  s/some^lSead^ 
escape,  so  none  could  be  observed  afterward— so  ^'^^^y-^ 
rapidly  was  the  part  healed,  feut  these  observations  did  not  attract 
much  notice  until  the  phenomena  of  escape  of  the  blood-corpuscles  from 
the  capillaries  and  minute  veins,  apart  from  mechanical  injury,  were  re- 
discovered by  Professor  Cohnheim  in  1867. 

Cohnheim^s  experiment  demonstrating  the  passage  of  the  corpuscles 
through  the  wall  of  the  blood-vessel,  is  performed  in  the  following  man- 


160 


HAra-BOOK  OF  PHYSIOLOGY. 


ner.  A  frog  is  urarized,  that  is  to  say,  paral3^sis  is  produced  by  inject- 
ing under  the  skin  a  minute  quantity  of  tlie  poison  called  urari;  and  the 
abdomen  having  been  opened,  a  portion  of  small  intestine  is  drawn  out, 
and  its  transparent  mesentery  spread  out  under  a  microscope.  After  a 
variable  time,  occupied  by  dilatation,  following  contraction  of  the  minute 
vessels  and  accompanying  quickening  of  the  blood-stream,  there  ensues  a 
retardation  of  the  current,  and  blood-corpuscles,  both  red  and  white, 
begin  to  make  their  way  through  the  capillaries  and  small  veins. 

* 'Simultaneously  with  the  retardation  of  the  blood-stream,  the  leu- 
cocytes, instead  of  loitering  here  and  there  at  the  edge  of  the  axial  cur- 
rent, begin  to  crowd  in  numbers  against  the  vascular  wall.  In  this  way 
the  vein  becomes  lined  with  a  continuous  pavement  of  these  bodies,  which 
remain  almost  motionless,  notwithstanding  that  the  axial  current  sweeps 
by  them  as  continuously  as  before,  though  with  abated  velocity.  Now  is 
the  moment  at  which  the  eye  must  be  fixed  on  the  outer  contour  of  the 
vessel,  from  which,  here  and  there,  minute,  colorless,  button-shaped  ele- 
vations spring,  just  as  if  they  were  produced  by  budding  out  of  the  wall 
of  the  vessel  itself.  The  buds  increase  gradually  and  slowly  in  size,  until 
each  assumes  the  form  of  a  hemispherical  projection,  of  width  correspond- 
ing to  that  of  the  leucocyte.  Eventually  the  hemisphere  is  converted  into 
a  pear-shaped  body,  the  small  end  of  which  is  still  attached  to  the  surface 
of  the  vein,  while  the  round  part  projects  freely.  Gradually  the  little 
mass  of  protoplasm  removes  itself  further  and  further  away,  and,  as  it 
does  so,  begins  to  shoot  out  delicate  prongs  of  transpai'ent  protoplasm  from 
its  surface,  in  nowise  differing  in  their  aspect  from  the  slender  thread  by 
which  it  is  still  moored  to  the  vessel.  Finally  the  thread  is  severed  and 
the  process  is  complete."    (Burdon  Sanderson.) 

The  process  of  diapedesis  of  the  red  corpuscles,  which  occurs  under 
circumstances  of  impeded  venous  circulation,  and  consequently  in- 
creased blood-pressure,  resembles  closely  the  migration  of  the  leuco- 
cytes, with  the  exception  that  they  are  squeezed  through  the  wall  of 
the  vessel,  and  do  not,  like  them,  work  their  way  through  by  amoeboid 
movement. 

Various  explanations  of  these  remarkable  phenomena  have  been  sug- 
gested. Some  believe  that  minute  openings  {sfig?))af(7  or  pscu do  .^fo/uafa) 
between  contiguous  endothelial  cells  (p.  133)  provide  the  means  of  escape 
for  the  blood-corpuscles.  But  the  chief  share  in  the  process  is  to  be  found 
in  the  vital  endowments  witli  respect  to  uu')bility  and  contraction  of  the 
parts  concerned —both  of  the  corpuscles  (Bastian)  and  the  capillary  wall 
(Strieker).  Burdon-Sanderson  remarks,  "the  capillary  is  not  a  dead 
conduit,  but  a  tube  of  living  protoplasm.  There  is  no  difficulty  in  un- 
derstanding liow  the  membrane  may  open  to  allow  the  escape  of  leucocytes, 
and  close  again  after  they  have  passed  out;  for  it  is  one  of  the  most  strik- 
ing peculiarities  of  contractile  substance  that  when  two  parts  of  the  same 


CIRCULATION  OF  THE  BLOOD. 


161 


mass  are  separated,  and  again  brought  into  contact,  they  melt  together  as 
if  they  had  not  been  severed." 

Hitherto,  the  escape  of  the  corpuscles  from  the  interior  of  the  blood- 
vessels into  the  surrounding  tissues  has  been  studied  chiefly  in  connection 
with  pathology.  But  it  is  impossible  to  say,  at  present,  to  what  degree 
the  discovery  may  not  influence  all  present  notions  regarding  the  nutrition 
of  the  tissues,  even  in  health. 

Vital  Capillary  Force. — The  circulation  through  the  capillaries  must, 
of  necessity,  b  ^  largely  influenced  by  that  which  occurs  in  the  vssssls  on 
either  side  of  them — in  the  arteries  or  the  veins;  their  intermediate  posi- 
tion causing  them  to  feel  at  once,  so  to  speak,  any  alteration  in  the  size 
or  rate  of  the  arterial  or  venous  blood-stream.  Thus,  the  apparent  con- 
traction of  the  capillaries,  on  the  application  of  certain  irritating  sub- 
stances, and  during  fear,  and  their  dilatation  in  blushing,  may  be  referred 
to  the  action  of  the  small  arteries,  rather  than  to  that  of  the  capillaries 
themselves.  But  largely  as  the  capillaries  are  influenced  by  these,  and  by 
the  conditions  of  the  parts  which  surround  and  support  them,  their  own 
endowments  must  not  be  disregarded.  They  must  be  looked  upon,  not  as 
mere  passive  channels  for  the  passage  of  blood,  but  as  possessing  endow- 
ments of  their  own  (vital  capillary  force),  in  relation  to  the  circulation. 
The  capillary  wall  is  actively  living  and  contractile;  and  there  is  no  reason 
to  doubt  that,  as  such,  it  must  have  an  important  influence  in  connection 
with  the  blood-current. 

Blood-Pressure  in  the  Capillaries. — From  observations  upon  the 
web  of  the  frog's  foot,  the  tongue  and  mesentery  of  the  frog,  the  tails  of 
newts,  and  small  fishes  (Roy  and  Brown),  as  well  as  upon  the  skin  of  the 
finger  behind  the  nail  (Kries),  by  careful  estimation  of  the  amount  of 
pressure  required  to  empty  the  vessels  of  blood  under  various  conditions, 
it  appears  that  the  blood-pressure  is  subject  to  variations  in  the  capillaries, 
ajjparently  following  the  variations  of  that  of  the  arteries;  and  that  up  to 
a  certain  point,  as  the  extravascular  pressure  is  increased,  so  does  the  pulse 
in  the  arterioles,  capillaries,  and  venules  become  more  and  more  evident. 
The  pressure  in  the  first  case  (web  of  the  frog's  foot)  has  been  found  to 
be  equal  to  about  14  to  20  mm.  of  mercury;  in  other  experiments  to  be, 
equal  to  about  J-  to  \-  of  the  ordinary  arterial  pressure. 

The  CiRCULATioiNT  ix  the  Veiks, 

The  blood-current  in  the  veins  is  maintained  by  the  slight  vis  a  tergo 
remaining  of  the  contraction  of  the  left  ventricle.  Very  effectual  assist- 
ance, however,  to  the  flow  of  blood  is  afforded  by  the  action  of  the  muscles 
capable  of  pressing  on  such  veins  as  have  valves. 

The  effect  of  such  muscular  pressure  may  be  thus  explained.  When 
pressure  is  applied  to  any  part  of  a  vein,  and  the  current  of  blood  in  it  is 
Vol.  I.— 11. 


162 


HAND-BOOK  OF  PHYSIOLOGY. 


obstructed,  the  portion  behind  the  seat  of  pressure  becomes  swollen  and 
distended  as  far  back  as  to  the  next  pair  of  valves.  These,  acting  Hke  the 
semilunar  valves  of  the  heart,  and  being,  like  them,  inextensible  both  in 
themselves  and  at  their  margins  of  attachment,  do  not  follow  the  vein  in 
its  distension,  but  are  drawn  out  toward  the  axis  of  the  canal.  Then,  if 
the  pressure  continues  on  the  vein,  the  compressed  blood,  tending  to  move 
equall}^  in  all  directions,  presses  the  valves  down  into  contact  at  their 
free  edges,  and  they  close  the  vein  and  prevent  regurgitation  of  the  blood. 
Thus,  whatever  force  is  exercised  by  the  pressure  of  the  muscles  on  the 
veins,  is  distribtited  partly  in  pressing  the  blood  onward  in  the  proper 
course  of  the  circulation,  and  partly  in  pressing  it  backward  and  closing 
the  valves  behind  (Fig.  128,  A  and  B). 

The  circulation  might  lose  as  much  as  it  gains  by  such  compression  of 
the  veins,  if  it  were  not  for  the  numerous  anastomoses  by  which  they 
communicate,  one  with  another;  for  through  these,  the  closing  up  of  the 
venous  channel  by  the  backward  pressure  is  prevented  from  being  any 
serious  hindrance  to  the  circulation,  since  the  blood,  of  which  the  onward 
course  is  arrested  by  the  closed  valves,  can  at  once  pass  through  some 
anastomosing  channel,  and  proceed  on  its  way  b}^  another  vein.  Thus, 
therefore,  the  effect  of  muscular  pressure  upon  veins  which  have  valves, 
is  turned  almost  entirely  to  the  advantage  of  the  circulation;  the  pressure 
of  the  blood  onward  is  all  advantageous,  and  the  pressure  of  the  blood  back- 
ward is  prevented  from  being  a  hindrance  by  the  closure  of  the  valves  and 
the  anastomoses  of  the  veins. 

The  effects  of  such  muscular  pressure  are  well  shown  by  the  accelera- 
tion of  the  stream  of  blood  when,  in  venesection,  the  muscles  of  the  fore- 
arm are  put  in  action,  and  by  the  general  acceleration  of  the  circulation 
during  active  exercise:  and  the  numerous  movements  which  are  continu- 
ally taking  place  in  the  body  while  awake,  though  their  single  effects  may 
be  less  striking,  must  be  an  important  auxiliary  to  the  venous  circulation. 
Yet  they  are  not  essential;  for  the  venous  circulation  continues  unim- 
paired in  parts  at  rest,  in  paralyzed  limbs,  and  in  parts  in  which  the  veins 
are  not  subject  to  any  muscular  pressure. 

Rhythmical  Contraction  of  Veins.— In  the  web  of  the  bat's  wing, 
the  veins  are  furnished  Avitli  valves,  and  possess  the  remarkable  lU'operty  of 
rhythmical  contraction  and  dilatation,  whereby  the  current  of  blood  within 
them  is  distinctly  accelerated.  (Wharton  Jones.)  The  contraction  occurs, 
on  an  average,  about  ten  times  in  a  minute;  the  existence  of  valves  ]ire- 
vcnting  regurgitation,  the  entire  effect  of  tlie  contractions  was  auxiliary 
to  the  onward  current  of  blood.  Analogous  iihonomena  liave  boon  fre- 
quently observed  in  other  animals. 

Blood-Pressure  in  the  Veins. — 'l'li(0)loo(l-prossuro  gradually  falls 
as  we  proceed  from  tlie  lieart  to  the  arteries,  from  tliese  to  the  oajiillarios, 
and  tlu'iice  along  the  veins  to  the  right  auricle.    The  blood-jiressure  in 


CIRCULATION  OF  THE  BLOOD. 


163 


the  veins  is  nowhere  very  great,  but  is  greatest  in  the  small  veins,  while 
in  the  large  veins  toward  the  heart  the  pressure  becomes  negative,  or,  in 
other  words,  when  a  vein  is  put  in  connection  with  a  mea*curial  manometer 
the  mercury  will  fall  in  the  area  furthest  away  from  the  vein  and  will  rise 
in  the  area  nearest  the  vein,  having  a  tendency  to  suck  in  rather  than  to 
push  forward.  In  the  veins  in  the  neck  this  tendency  to  suck  in  air  is 
especially  marked,  and  is  the  cause  of  death  in  some  operations  in  that 
region.  The  amount  of  pressure  in  the  brachial  vein  is  said  to  support 
9  mm.  of  mercury,  whereas  the  pressure  in  the  veins  of  the  neck  is  about 
equal  to  a  negative  pressure  of  —3  to  —8  mm. 

The  variations  of  venous  pressure  during  systole  and  diastole  of  the 
heart  are  very  slight,  and  a  distinct  pulse  is  seldom  seen  in  veins  except 
under  very  extraordinary  circumstances. 

The  formidable  obstacle  to  the  upward  current  of  the  blood  in  the 
veins  of  the  trunk  and  extremities  in  the  erect  posture  supposed  to  be  pre- 
sented by  the  gravitation  of  the  blood,  has  no  real  existence,  since  the 
pressure  exercised  by  the  column  of  blood  in  the  arteries,  will  be  always 
sufficient  to  support  a  column  of  venous  blood  of  the  same  height  as  itself: 
the  two  columns  mutually  balancing  each  other.  Indeed,  so  long  as 
both  arteries  and  veins  contain  continuous  columns  of  blood,  the  force  of 
gravitation,  whatever  be  the  position  of  the  body,  can  have  no  power  to 
move  or  resist  the  motion  of  any  part  of  the  blood  in  any  direction.  The 
lowest  blood-vessels  have,  of  course,  to  bear  the  greatest  amount  of  pres- 
sure; the  pressure  on  each  part  being  directly  proportionate  to  the  height 
of  the  column  of  blood  above  it:  hence  their  liability  to  distension.  But 
this  pressure  bears  equally  on  both  arteries  and  veins,  and  cannot  either 
move,  or  resist  the  motion  of,  the  fluid  they  contain,  so  long  as  the  col- 
umns of  fluid  are  of  equal  height  in  both,  and  continuous. 

Velocity  of  the  Circulation. 

The  velocity  of  the  blood-current  at  any  given  point  in  the  various 
divisions  of  the  circulatory  system  is  inversely  proportional  to  their 
sectional  area  at  that  point.  If  the  sectional  area  of  all  the  branches 
of  a  vessel  united  were  always  the  same  as  that  of  the  vessel  from  which 
they  arise,  and  if  the  aggregate  sectional  area  of  the  capillary  vessels 
were  equal  to  that  of  the  aorta,  the  mean  rapidity  of  the  blood^s  motion 
in  the  capillaries  would  be  the  same  as  in  the  aorta  and  largest  arteries; 
and  if  a  similar  correspondence  of  capacity  existed  in  the  veins  and 
arteries,  there  would  be  an  equal  correspondence  in  the  rapidity  of  the 
circulation  in  them.  But  the  arterial  and  venous  systems  may  be  re]3- 
resented  by  two  truncated  cones  with  their  apices  directed  toward  the 
heart;  the  area  of  their  united  base  (the  sectional  area  of  the  capillaries) 
being  400 — 800  times  as  great  as  that  of  the  truncated  apex  representing 


164  HAND-BOOK  OF  PHYSIOLOGY. 


the  aorta.  Thus  the  velocity  of  blood  in  the  capillaries  is  at  least  of 
that  in  the  aorta. 

Velocity  in  the  Arteries. — The  velocity  of  the  stream  of  blood  is 
greater  in  the  arteries  than  in  any  other  part  of  the  circulatory  system, 
and  in  them  it  is  greatest  in  the  neighborhood  of  the  heart,  and  during 
the  ventricular  systole;  the  rate  of  movement  diminishing  during  the  dias- 
tole of  the  ventricles,  and  in  the  parts  of  the  arterial  system  most  distant 
from  the  heart.  Ohauveau  has  estimated  the  rapidity  of  the  blood- 
stream in  the  carotid  of  the  horse  at  over  20  inches  per  second  during  the 
hearths  systole,  and  nearly  6  inches  during  the  diastole  (520 — 150  mm.). 

Estimation  of  the  Velocity. — Various  instruments  have  been  devised 
for  measuring  the  velocity  of  the  blood-stream  in  the  arteries.  Ludwig's 
^^Stromuhr'-  (Fig.  142)  consists  of  a  U-shaped  glass  tube 
dilated  at  a  and  a',  and  whose  extremities,  h  and  i,  are 
of  known  calibre.  The  bulbs  can  be  filled  by  a  common 
opening  at  Ic.  The  instrument  is  so  contrived  that  at  !> 
and  i'  the  glass  part  is  firmly  fixed  into  metal  cylinders, 
which  are  fixed  into  a  circular  horizontal  table,  c  c' ,  capa- 
ble of  horizontal  movement  on  a  similar  table  d  d'  about 
the  vertical  axis  marked  in  figure  by  a  dotted  line.  The 
opening  in  c  c',  when  the  instrument  is  in  position,  as  in 
Fig.,  corresponds  exactly  with  those  in  d  d'\  but  if  c 
be  turned  at  right  angles  to  its  present  position,  there 
is  no  communication  between  li  and  a,  and  i  and 
but  li  communicates  directly  with  i\  and  if  turned 
through  two  right  angles  c'  communicates  with  d,  and 
c  with  d' ,  and  there  is  no  direct  connection  between  li 
and  i.  The  experiment  is  performed  in  the  following- 
way: — The  artery  to  be  experimented  upon  is  divided 
and  connected  with  two  cannulae  and  tubes  which  fit  it 
accurately  with  li  and  i — li  the  central  end,  and  %  the 
peripheral;  the  bulb  a  is  filled  with  olive  oil  up  to  a  point 
rather  lower  than  h,  and  a'  and  the  remainder  of  a  is  filled  with  defibri- 
nated  blood;  the  tube  on  Tc  is  then  carefully  clamped;  the  tubes  6?  and 
d'  are  also  filled  with  defibrinated  blood.  When  everything  is  ready,  the 
blood  is  allowed  to  flow  into  a  through  //,  and  it  pushes  before  it  the  oil, 
and  that  the  defibrinated  blood  into  the  artery  through  /,  and  replaces 
it  in  a'\  when  the  blood  reaches  the  former  level  of  the  oil  in  a,  the  disc 
c  6''  is  turned  rapidly  through  two  right  angles,  and  the  blood  flowing 
through  d  into  a*  again  displaces  the  oil  which  is  driven  into  a.  This 
is  repeated  several  times,  and  the  duration  of  the  experiment  noted. 
Tlic  capacity  of  a  and  a'  is  kiuown;  the  diameter  of  the  artery  is  also 
known  by  its  corresponding  with  the  cannuliB  of  known  diameter,  and  us 
the  number  of  times  a  has  been  tilled  in  a  given  time  is  known,  tho 
velocity  of  the  current  can  bo  calculated. 


Fig.  142.— Ludwig's 
Stromuhr. 


CIRCULATION  OF  THE  BLOOD. 


1G5 


Chauveau's  instrument  (Fig.  143)  consists  of  a  thin  brass  tube,  a,  in 
one  side  of  which  is  a  small  perforation  closed  by  thin  vulcanized  india- 
rubber.  Passing  through  the  rubber  is  a  fine  lever,  one  end  of  which, 
slightly  flattened,  extends  into  the  lumen  of  the  tube,  while  the  other 
moves  over  the  face  of  a  dial.    The  tube  is  inserted  into  the  interior  of 


Fig.  143.— Diagram  of  Chauveau's  Instrument,  a.  Brass  tube  for  introduction  into  the  lumen  ot 
the  artery,  and  containing  an  index-needle,  which  passes  through  the  elastic  membrane  in  its  side, 
and  moves  by  the  impulse  of  the  blood-current,  c.  Graduated  scale,  for  measuring  the  extent  of  the 
oscillations  of  the  needle. 

an  artery,  and  ligatures  applied  to  fix  it,  so  that  the  movement  of  the 
blood  may,  in  flowing  through  the  tube,  be  indicated  by  the  movement  of 
the  outer  extremity  of  the  lever  on  the  face  of  the  dial. 

The  HcBmatocliometer  of  Vierordt,  and  the  instrument  of  Lortet, 
resemble  in  principle  that  of  Chauveau. 

Velocity  in  the  Capillaries. — The  observations  of  Hales,  E.  H. 
AVeber,  and  Valentin  agree  very  closely  as  to  the  rate  of  the  blood-current 
in  the  capillaries  of  the  frog;  and  the  mean  of  their  estimates  gives  the 
velocity  of  the  systemic  capillary  circulation  at  about  one  inch  (25  mm.) 
per  minute.  The  velocity  in  the  capillaries  of  warm-blooded  animals  is 
greater.  In  the  dog  ^  to  jIq-  inch  (-5  to  '75  mm.)  a  second.  This  may 
seem  inconsistent  with  the  facts  which  show  that  the  whole  circulation  is 
accomplished  in  about  half  a  minute.  But  the  whole  length  of  capillary 
vessels,  through  which  any  given  portion  of  blood  has  to  pass,  probably 
does  not  exceed  from  -g^th  to  -^V^h  of  an  inch  ( -5  mm. ) ;  and  therefore 
the  time  required  for  each  quantity  of  blood  to  traverse  its  own  appointed 
portion  of  the  general  capillary  system  will  scarcely  amount  to  a  second. 

Velocity  in  the  Veins. — The  velocity  of  the  blood  is  greater  in  the 
veins  than  in  the  capillaries,  but  less  than  in  the  arteries:  this  fact 
depending  upon  the  relative  capacities  of  the  arterial  and  venous  systems. 
If  an  accurate  estimate  of  the  proportionate  areas  of  arteries  and  the  veins 
corresponding  to  them  could  be  made,  we  might,  from  the  velocity  of  the 
arterial  current,  calculate  that  of  the  venous.  A  usual  estimate  is,  that 
the  capacity  of  the  veins  is  about  twice  or  three  times  as  great  as  that  of 
the  arteries,  and  that  the  velocity  of  the  blood^s  motion  is,  therefore. 


166 


HAND-BOOK  OF  PHYSIOLOGY. 


about  twice  or  three  times  as  great  in  the  arteries  as  in  the  veins,  8  inches 
(about  200  mm.)  a  second.  The  rate  at  which  the  blood  moves  in  the 
veins  gradually  increases  the  nearer  it  approaches  the  heart,  for  the  sec- 
tional area  of  the  venous  trunks,  compared  with  that  of  the  branches 
opening  into  them,  becomes  gradually  less  as  the  trunks  advance  toward 
the  heart. 

Velocity  of  the  Circulation  as  a  whole.— It  would  appear  that  a 
portion  of  blood  can  traverse  the  entire  course  of  the  circulation,  in  the 
horse,  in  half  a  minute.  Of  course  it  would  require  longer  to  traverse 
the  vessels  of  the  most  distant  part  of  the  extremities  than  to  go  through 
those  of  the  neck:  but  taking  an  average  length  of  vessels  to  be  traversed, 
and  assuming,  as  we  may,  that  the  movement  of  blood  in  the  human 
subject  is  not  slower  than  in  the  horse,  it  may  be  concluded  that  half  a 
minute  represents  the  average  rate. 

Satisfactory  data  for  these  estimates  are  afforded  by  the  results  of 
experiments  to  ascertain  the  rapidity  with  which  poisons  introduced  into 
the  blood  are  transmitted  from  one  part  of  the  vascular  system  to 
another.  The  time  required  for  the  passage  of  a  solution  of  potassium 
ferrocyanide,  mixed  with  the  blood,  from  one  jugular  vein  (through  the 
right  side  of  the  heart,  the  pulmonary  vessels,  the  left  cavities  of  the 
heart,  and  the  general  circulation)  to  the  jugular  vein  of  the  opposite 
side,  varies  from  twenty  to  thirty  seconds.  The  same  substance  was 
transmitted  from  the  jugular  vein  to  the  great  saphena  in  twenty  seconds; 
from  the  jugular  vein  to  the  masseteric  artery,  in  between  fifteen  and 
thirty  seconds;  to  the  facial  artery,  in  one  experiment,  in  between  ten 
and  fifteen  seconds;  in  another  experiment  in  between  twenty  and  twenty- 
five  seconds;  in  its  transit  from  the  jugular  vein  to  the  metatarsal  artery, 
it  occupied  between  twenty  and  thirty  seconds,  and  in  one  instance  more 
than  forty  seconds.  The  result  was  nearly  the  same  whatever  was  the 
rate  of  the  hearths  action. 

In  all  these  experiments,  it  is  assumed  that  the  substance  injected 
moves  with  the  blood,  and  at  the  same  rate,  and  does  not  move  from  one 
part  of  the  organs  of  circulation  to  another  by  diffusing  itself  through  the 
blood  or  tissues  more  quickly  tlian  the  blood  moves.  The  assumption  is 
sufficiently  probable,  to  be  considered  nearly  certain,  that  the  times  above 
mentioned,  as  occupied  in  tlie  passage  of  the  injected  substances,  are 
those  in  which  tlie  portion  of  blood,  into  whicli  each  was  injected,  was 
carried  from  one  part  to  another  of  the  vascular  system. 

Another  mode  of  estimating  the  general  velocity  of  the  circulating 
blood,  is  by  calculating  it  from  the  quantity  of  blood  su})posed  to  bo  con- 
tained in  the  body,  and  from  the  quantity  whicli  can  })ass  through  the 
heart  in  each  of  its  actions.  But  the  conclusions  arrived  at  by  this 
metliod  are  less  satisfactory.  For  the  estimates  both  of  the  total  (]uantity 
of  blood,  and  of  the  capacity  of  the  cavities  of  the  heart,  have  as  yet  only 


CIRCULATION  OF  THE  BLOOD. 


167 


approximated  to  the  truth.  Still  the  most  careful  of  the  estimates  thus 
made  accord  very  nearly  with  those  already  mentioned;  and  it  may  be 
assumed  that  the  blood  may  all  pass  through  the  heart  in  from  twenty- 
five  to  fifty  seconds. 

Peculiarities  of  the  Circulation  in  Different  Parts. — The  most 
remarkable  peculiarities  attending  the  circulation  of  blood  through  differ- 
ent organs  are  observed  in  the  cases  of  the  hrain,  the  erectile  organs,  the 
lungs,  the  liver,  and  the  kidney. 

1.  In  the  Brain. — For  the  due  performance  of  its  functions,  the  brain 
requires  a  large  supply  of  blood.  This  object  is  effected  through  the 
number  and  size  of  its  arteries,  the  two  internal  carotids,  and  the  two 
vertehrals.  It  is  further  necessary  that  the  force  with  which  this  blood  is 
sent  to  the  brain  should  be  less,  or  at  least  should  be  subject  to  less  vari- 
ation from  external  circumstances  than  it  is  in  other  parts,  and  so  the 
large  arteries  are  very  tortuous  and  anastomose  freely  in  the  circle  of 
Willis,  which  thus  insures  that  the  supply  of  blood  to  the  brain  is  uni- 
form, though  it  may  by  an  accident  be  diminished,  or  in  some  way 
changed,  through  one  or  more  of  the  principal  arteries.  The  transit  of 
the  large  arteries  through  bone,  especially,  the  carotid  canal  of  the  tem- 
poral bone,  may  prevent  any  undue  distension;  and  uniformity  of  supply 
is  further  insured  by  the  arrangement  of  the  vessels  in  the  pia  mater,  in 
which,  previous  to  their  distribution  to  the  substance  of  the  brain,  the 
large  arteries  break  up  and  divide  into  innumerable  minute  branches 
ending  in  capillaries,  which,  after  frequent  communications  with  one 
another,  enter  the  brain,  and  carry  into  nearly  every  part  of  it  uniform 
and  equable  streams  of  blood.  The  arteries  are  also  enveloped  in  a  special 
lymphatic  sheath.  The  arrangement  of  the  veins  within  the  cranium  is 
also  peculiar.  The  large  venous  trunks  or  sinuses  are  formed  so  as  to  be 
scarcely  capable  of  change  of  size;  and  composed,  as  they  are,  of  the 
tough  tissue  of  the  dura  mater,  and,  in  somo  instances,  bounded  on  one 
side  by  the  bony  cranium,  they  are  not  compressible  by  any  force  which 
the  fulness  of  the  arteries  might  exercise  through  the  substance  of  the 
brain;  nor  do  they  admit  of  distension  when  the  flow  of  venous  blood 
from  the  brain  is  obstructed. 

The  general  uniformity  in  the  supply  of  blood  to  the  brain,  which  is 
thus  secured,  is  well  adapted,  not  only  to  its  functions,  but  also  to  its  con- 
dition as  a  mass  of  nearly  incompressible  substance  placed  in  a  cavity 
with  unyielding  walls.  These  conditions  of  the  brain  and  skull  have 
appeared,  indeed,  to  some,  enough  to  justify  the  opinion  that  the  quan- 
tity of  blood  in  the  brain  must  be  at  all  times  the  same.  It  was  found 
that  in  animals  bled  to  death,  without  any  aperture  being  made  in  the 
cranium,  the  brain  became  pale  and  anaemic  like  other  parts.  And  in 
death  from  strangling  or  drowning,  congestion  of  the  cerebral  vessels; 
while  in  death  by  prussic  acid,  the  quantity  of  blood  in  the  cavity  of  the 


168 


HAISTD-BOOK  OF  PHYSIOLOGY. 


cranium  was  determined  by  the  position  in  which  the  animal  was  placed 
after  death,  the  cerebral  vessels  being  congested  when  the  animal  was  sus- 
pended with  its  head  downward,  and  comparatively  empty  when  the 
animal  was  kept  suspended  by  the  ears.  That,  it  was  concluded,  although 
the  total  volume  of  the  contents  of  the  cranium  is  probably  nearly  always 
the  same,  yet  the  quantity  of  blood  in  it  is  liable  to  variation,  its  increase 
or  diminution  being  accompanied  by  a  simultaneous  diminution  or  in- 
crease in  the  quantity  of  the  cerebro-spinal  fluid,  which,  by  readily 
admitting  of  being  removed  from  one  part  of  the  brain  and  spinal  cord  to 
another,  and  of  being  rapidly  absorbed,  and  as  readily  effused,  would 
serve  as  a  kind  of  supplemental  fluid  to  the  other  contents  of  the  cranium, 
to  keep  it  uniformly  filled  in  case  of  variations  in  their  quantity  (Bur- 
rows). And  there  can  be  no  doubt  that,  although  the  arrangements  of 
the  blood-vessels,  to  which  reference  has  been  made,  ensure  to  the  brain 
an  amount  of  blood  which  is  tolerably  uniform,  yet,  inasmuch  as  with 
every  beat  of  the  heart  and  every  act  of  respiration,  and  under  many 
other  circumstances,  the  quantity  of  blood  in  the  cavity  of  the  cranium 
is  constantly  varying,  it  is  plain  that,  were  there  not  provision  made  for 
the  possible  displacement  of  some  of  the  contents  of  the  unyielding  bony 
case  in  which  the  brain  is  contained,  there  would  be  often  alternations  of 
excessive  pressure  with  insufficient  supply  of  blood.  Hence  we  may  con- 
sider that  the  cerebro-spinal  fluid  in  the  interior  of  the  skull  not  only 
subserves  the  mechanical  functions  of  fat  in  other  parts  as  'd.  paching 
material,  but  by  the  readiness  with  which  it  can  be  displaced  into  the 
spinal  canal,  provides  the  means  whereby  undue  pressure  and  insufficient 
supply  of  blood  are  equally  prevented. 

Chemical  Composition  of  Cerebro-spinal  Fluid. — The  cerebro-spinal 
fluid  is  transparent,  colorless,  not  viscid,  with  a  saline  taste  and  alkaline 
reaction,  and  is  not  affected  by  heat  or  acids.  It  contains  981-984  parts 
water,  sodium  chloride,  traces  of  potassium  chloride,  of  sulphates,  car- 
l)onates,  alkaline  and  earthy  phosphates,  minute  traces  of  urea,  sugar, 
sodium  lactate,  fatty  matter,  cholesterin,  and  albumen  (Flint). 

2.  Li  Erectile  Structures. — The  instances  of  greatest  variation  in  the 
quantity  of  blood  contained,  at  different  times,  in  the  same  organs,  are 
found  in  certain  structures  which,  under  ordinary  circumstances,  are  soft 
and  flaccid,  but,  at  certain  times,  receive  an  unusually  large  quantity  of 
blood,  become  distended  and  swollen  by  it,  and  pass  into  the  state  which 
has  been  termed  erection.  Such  structures  are  the  corpora  cavernosa  and 
corpus  sporujiositm,  of  the  penis  in  the  male,  and  the  clitoris  in  the  female: 
tmd,  to  a  less  degree,  the  nipple  of  tlie  mammary  gland  in  botli  sexes. 
The  corpus  cavei-nosum  penis,  which  is  the  best  example  of  an  erectile 
stru(;tiire,  has  an  external  lil)rous  nuMnbrane  or  sheath;  and  from  the 
inner  surface  of  the  latter  are  ])rolonged  numerous  lino  lamelli\3  which 


CIRCULATION  OF  THE  liLOOD. 


1G9 


divide  its  cavity  into  small  compartments  looking  like  cells  when  they 
are  inflated.  Within  these  is  situated  the  plexus  of  veins  upon  which 
the  peculiar  erectile  property  of  the  organ  mainly  depends.  It  consists 
of  short  veins  which  very  closely  interlace  and  anastomose  with  each  other 
in  all  directions,  and  admit  of  great  variation  of  size,  collapsing  in  the 
passive  state  of  the  organ,  but,  for  erection,  capable  of  an  amount  of  dila- 
tation which  exceeds  beyond  comparison  that  of  the  arteries  and  veins 
which  convey  the  blood  to  and  from  them.  The  strong  fibrous  tissue 
lying  in  the  intervals  of  the  venous  plexuses,  and  the  external  fibrous 
membrane  or  sheath  with  which  it  is  connected,  limit  the  distension  of 
the  vessels,  and,  during  the  state  of  erection,  give  to  the  penis  its  con- 
dition of  tension  and  firmness.  The  same  general  condition  of  vessels 
exists  in  the  corpus  spongiosum  urethrae,  but  around  the  urethra  the 
fibrous  tissue  is  much  weaker  than  around  the  body  of  the  penis,  and 
around  the  glans  there  is  none.  The  venous  blood  is  returned  from  the 
plexuses  by  comparatively  small  veins;  those  from  the  glans  and 
the  fore  part  of  the  urethra  empty  themselves  into  the  dorsal  veins  of  the 
penis;  those  from  the  cavernosum  pass  into  deeper  veins  which  issue  from 
the  corpora  cavernosa  at  the  crura  penis;  and  those  from  the  rest  of  the 
urethra  and  bulb  pass  more  directly  into  the  plexus  of  the  veins  about  the 
prostate.  For  all  these  veins  one  condition  is  the  same;  namely,  that 
they  are  liable  to  the  pressure  of  muscles  when  they  leave  the  penis.  The 
muscles  chiefly  concerned  in  this  action  are  the  erector  penis  and  acceler- 
ator urinae.  Erection  results  from  the  distension  of  the  venous  plexuses 
with  blood.  The  principal  exciting  cause  in  the  erection  of  the  penis  is 
nervous  irritation,  originating  in  the  part  itself,  or  derived  from  the  brain 
and  spinal  cord.  The  nervous  influence  is  communicated  to  the  j)enis  by 
the  pudic  nerves,  which  ramify  in  its  vascular  tissue:  and  after  their 
division  in  the  horse,  the  penis  is  no  longer  capable  of  erection. 

This  influx  of  the  blood  is  the  first  condition  necessary  for  erection, 
and  through  it  alone  much  enlargement  and  turgescence  of  the  penis 
may  ensue.  But  the  erection  is  probably  not  complete,  nor  maintained 
for  any  time  except  when,  together  with  this  influx,  the  muscles  already 
mentioned  contract,  and  by  compressing  the  veins,  stop  the  efflux  of 
blood,  or  prevent  it  from  being  as  great  as  the  influx. 

It  appears  to  be  only  the  most  perfect  kind  of  erection  that  needs  the 
help  of  muscles  to  compress  the  veins;  and  none  such  can  materially  as- 
sist the  erection  of  the  nippies,  or  that  amount  of  turgescence,  just  falling 
short  of  erection,  of  which  the  spleen  and  many  other  parts  are  capable. 
For  such  turgescence  nothing  more  seems  necessary  than  a  large  plexiform 
arrangement  of  the  veins,  and  such  arteries  as  may  admit,  upon  occasion, 
augmented  quantities  of  blood. 

(3,  4,  5.)  The  circulation  in  the  Lungs,  Liver,  and  Kidneys  will  be 
described  under  those  heads. 


170 


HAND-BOOK  OF  PHYSIOLOGY. 


Agents  concerned  in  the  circulation. — Before  quitting  this  sub- 
ject it  will  be  as  well  to  bring  together  in  a  tabular  form  the  various 
agencies  concerned  in  maintaijiing  the  circulation. 

1.  The  Systole  and  Diastole  of  the  Heart,  the  former  pumping  into 
the  aorta  and  so  into  the  arterial  system  a  certain  amount  of  blood,  and 
the  latter  to  some  extent  sucking  in  the  blood  from  the  veins. 

2.  Tlie  elastic  and  muscular  coats  of  the  arteries,  which  serve  to  keep 
up  an  equable  and  continuous  stream. 

3.  The  so-called  vital  cajnllary  force. 

4.  The  pressure  of  the  muscles  on  veins  with  valves,  and  the  slight 
rhythmic  contraction  of  the  veins. 

5.  Aspiration  of  the  Thorax  during  inspiration,  by  means  of  which 
the  blood  is  drawn  from  the  large  veins  into  the  thorax  (to  be  treated  of 
in  next  Chapter). 

DiSCOVEEY  OF  THE  ClECULATIO^T. 

Up  to  nearly  the  close  of  the  sixteenth  century  it  was  generally  be- 
lieved that  the  blood  passed  from  one  ventricle  to  the  other  through  fora- 
mina in  the  "septum  ventriculorum."^  These  foramina  are  of  course 
purely  imaginary,  but  no  one  ventured  to  dispute  their  existence  till  Ser- 
vetus  boldly  stated  that  he  could  not  succeed  in  finding  them.  He  fur- 
ther asserted  that  the  blood  passed  from  the  Eight  to  the  Left  side  of  the 
heart  by  way  of  the  lungs,  and  also  advanced  the  hypothesis  that  it  is  thus 
"revivified,^"  remarking  that  the  Pulmonary  Artery  is  too  large  to  serve 
merely  for  the  nutrition  of  the  lungs  (a  theory  then  generally  accepted). 

Eealdus,  Columbo,  and  Csesalpinus  added  several  important  observa- 
tions. The  latter  showed  that  the  blood  is  slightly  cooled  by  passing 
through  the  lungs,  also  that  the  veins  swell  up  on  the  distal  side  of  a  liga- 
ture. The  existence  of  valves  in  the  veins  had  previously  been  discovered 
by  Fabricius  of  Aquapendente,  the  teacher  of  Harvey. 

The  honor  of  first  demonstrating  the  general  course  of  the  circulation 
belongs  by  right  to  Harvey,  who  made  his  grand  discovery  about  1G18. 
He  was  the  first  to  establish  the  muscular  structure  of  the  heart,  which 
had  been  denied  by  many  of  his  predecessors;  and  by  careful  study  of  its 
action  both  in  the  body  and  when  excised,  ascertained  the  order  of  con- 
traction of  its  cavities.  He  did  not  content  himself  with  inferences  from 
the  anatomy  of  the  parts,  bat  employed  the  experimental  method  of 
injection,  and  made  an  extensive  and  accurate  series  of  observations  on 
the  circulation  in  cold-blooded  animals.  He  forced  water  through  the 
Pulmonary  Artery  till  it  trickled  out  through  the  Left  Ventricle,  the  tip 
of  which  had  been  cut  off.  Another  of  his  experiments  was  to  fill  the 
Riglit  side  of  the  heart  with  water,  tie  the  Pulmonary  Artery  and  the 
Ventv  Cava?  and  then  squeeze  the  Right  ventricle:  not  a  drop  could  be 
forced  throiigli  into  the  Left  ventricle,  and  thus  lie  conclusively  disproved 
the  existence  of  foramina  in  the  septum  ventriculorum.  "I  have  suffi- 
ciently proved,"  says  lie,  "that  by  the  beatino;  of  the  heart  the  blood 
passes  from  the  veins  into  tlie  arteries  tlirougli  the  ventricles,  and  is  dis- 
tributed over  X\\i\  wliole  body." 

"In  the  warmer  aninuils,  sucli  as  man,  the  blood  pusses  from  the  Eight 


CIKCULATION  OF  TJIE  BLOOD. 


171 


Ventricle  of  the  Heart  through  the  Pulmonary  Artery  into  the  Lungs, 
and  thence  through  the  Pulmonary  Veins  into  the  Left  Auricle,  thence 
into  the  Left  Ventricle." 

Proofs  of  the  Circulation  of  the  Blood. — The  following  are  the 
main  arguments  by  which  Harvey  established  the  fact  of  the  circulation: — 

1.  The  heart  in  half  an  hour  propels  more  blood  than  the  whole  mass 
of  blood  in  the  body. 

2.  The  great  force  and  jetting  manner  with  which  the  blood  spurts 
from  an  opened  artery,  such  as  the  carotid,  with  every  beat  of  the  heart. 

3.  If  true,  the  normal  course  of  the  circulation  explains  why  after 
death  the  arteries  are  commonly  found  empty  and  the  veins  full. 

4.  If  the  large  veins  near  the  heart  were  tied  in  a  fish  or  snake,  the 
heart  became  pale,  flaccid,  and  bloodless;  on  removing  the  ligature,  the 
blood  again  flowed  into  the  heart.  If  the  artery  were  tied,  the  heart  be- 
came distended;  the  distension  lasting  until  the  ligature  was  removed. 

5.  The  evidence  to  be  derived  from  a  ligature  round  a  limb.  If  it  be 
drawn  very  tight,  no  blood  can  enter  the  limb,  and  it  becomes  pale  and 
cold.  If  the  ligature  be  somewhat  relaxed,  blood  can  enter  but  cannot 
leave  the  limb;  hence  it  becomes  swollen  and  congested.  If  the  ligature 
be  removed,  the  limb  soon  regains  its  natural  appearance. 

6.  The  existence  of  valves  in  the  veins  which  only  permit  the  blood 
to  flow  toward  the  heart. 

7.  The  general  constitutional  disturbance  resulting  from  the  introduc- 
tion of  a  poison  at  a  sijagle  point,  e.  g.,  snake  poison. 

To  these  may  now  be  added  many  further  proofs  which  have  accumu- 
lated since  the  time  of  Harvey,  e.  g. : — 

8.  Wounds  of  arteries  and  veins.  In  the  former  case  haemorrhage  may 
be  almost  stopped  by  pressure  between  the  heart  and  the  wound,  in  the 
latter  by  pressure  beyond  the  seat  of  injury. 

9.  The  direct  observation  of  the  passage  of  blood  corpuscles  from 
small  arteries  through  capillaries  into  veins  in  all  transparent  vascular 
parts,  as  the  mesentery,  tongue  or  web  of  the  frog,  the  tail  or  gills  of  a 
tadpole,  etc. 

10.  The  results  of  injecting  certain  substances  into  the  blood. 
Further,  it  is  obvious  that  the  mere  fact  of  the  existence  of  a  hollow 

muscular  organ  (the  heart)  with  valves  so  arranged  as  to  permit  the  blood 
to  pass  only  in  one  direction,  of  itself  suggests  the  course  of  the  circula- 
tion. The  only  part  of  the  circulation  which  Harvey  could  not  follow 
is  that  through  the  capillaries,  for  the  simple  reason  that  he  had  no  lenses 
sufficiently  powerful  to  enable  him  to  see  it.  Malpighi  (1661)  and  Leeu- 
wenhoek  (1668)  demonstrated  it  in  the  tail  of  the  tadpole  and  lung  of  the 
frog. 


CHAPTEE  YI. 


RESPIRATION. 

The  maintenance  of  animal  life  necessitates  the  continual  absorption 
of  oxygen  and  excretion  of  carbonic  acid;  the  blood  being,  in  all  animals 
which  possess  a  well  developed  blood-vascular  system,  the  medium  by 
which  these  gases  are  carried.  By  the  blood,  oxygen  is  absorbed  from 
without  and  conveyed  to  all  parts  of  the  organism,  and,  by  the  blood, 
carbonic  acid,  which  comes  from  within,  is  carried  to  those  parts  by 
which  it  may  escape  from  the  body.  The  two  processes, — absorption 
of  oxygen  and  excretion  of  carbonic  acid, — are  complementary,  and 
their  sum  is  termed  the  process  of  Respiration. 

In  all  Yertebrata,  and  in  a  large  number  of  Invertebrata,  certain  parts, 
either  lungs  or  gills,  are  specially  constructed  for  bringing  the  blood  into 
proximity  with  the  aerating  medium  (atmospheric  air,  or  water  contain- 
ing air  in  solution).  In  some  of  the  lower  Vertebrata  (frogs  and  other 
naked  Amphibia)  the  skin  is  important  as  a  respiratory  organ,  and  is 
capable  of  supplementing,  to  some  extent,  the  functions  of  the  j!?rojt;er 
hreatldng  apparatus;  but  in  all  the  higher  animals,  including  man,  the 
respiratory  capacity  of  the  skin  is  so  infinitesimal  that  it  may  be  practi- 
cally disregarded. 

Essentially,  a  lung  or  gill  is  constructed  of  a  fine  transparent  mem- 
brane, one  surface  of  which  is  exposed  to  the  air  or  water,  as  the  case  ma}^ 
be,  while,  on  the  other,  is  a  network  of  blood-vessels, — the  only  separation 
between  the  blood  and  aerating  medium  being  the  thin  wall  of  the  blood- 
vessels, and  the  fine  membrane  on  one  side  of  which  vessels  are  distributed. 
The  difference  between  the  simplest  and  the  most  complicated  respiratory 
membrane  is  one  of  degree  only. 

The  various  complexity  of  the  respiratory  membrane,  and  the  kind  of 
aerating  medium,  are  not,  however,  the  only  conditions  which  cause  a 
difference  in  the  respiratory  capacity  of  different  animals.  The  number 
and  size  of  the  red  blood-corpuscles,  the  mechanism  of  the  breatliing  ap- 
pji.ratus,  the  i)resence  or  absence  of  a  pnlmonarii  heart,  physiologically 
distinct  from  the  systemic,  are,  all  of  them,  conditions  scarcely  second 
in  importance. 

In  the  heart  of  man  and  all  other  l\ranim;]lia,  the  r////// side  from  which 
the  blood  is  propelled  into  and  through  the  lungs  may  be  termed  the 


RESPIRATION. 


175 


•'puiiryoTiary^^  heart;  while  the  left  side  is  "  systemic in  function.  In 
many  ui'  the  lower  animals,  however,  no  such  distinction  can  be  drawn. 
Thus,  m  Fish  the  heart  propels  the  blood  to  the  respiratory  organ  (gills); 
but  tiiere  is  no  contractile  sac  corresponding  to  tlie  left  side  of  the  heart, 
to  propel  the  blood  directly  into  the  systemic  vessels. 

It  may  be  well  to  state  here  that  the  lungs  are  only  the  medium  for 
the  exchange,  on  the  part  of  the  blood,  of  carbonic  acid  for  oxygen.  They 
are  not  the  seat,  in  any  special  manner,  of  those  combustion-processes 
of  which  the  production  of  carbonic  acid  is  the  final  result.  These  occur 
in  all  parts  of  the  body — more  in  one  part,  less  in  another:  chiefly  in  the 
substance  of  the  tissues,  but  in  part  in  the  capillary  blood-vessels  contained 
in  them. 

The  Kespiratory  Passages  akd  Tissues. 

The  object  of  respiration  is  the  interchange  of  gases  in  the  lungs;  for 
this  purpose  it  is  necessary  that  the  atmospheric  air  shall  pass  into  them 


Fig.  144. 


and  be  expelled,  from  them.  The  lungs  are  contained  in  the  chest  or 
thorax,  which  is  a  closed  cavity  having  no  communication  with  the  out- 


174 


HAl^D-BOOK  OF  PHYSIOLOGY. 


side^  except  by  means  of  the  respiratory  passages.  The  air  enters  these 
passages  through  the  nostrils  or  through  the  mouthy  thence  it  passes 
through  the  larynx  into  the  trachea  or  windpipe^  which  about  the  middle 
of  the  chest  divides  into  two  tubes,  hroncM,  one  to  each  (right  and  left) 
lung. 

The  Larynx  is  the  upper  part  of  the  passage  whicn  leaas  exclusively 
to  the  lung;  it  is  formed  by  the  thyroid,  cricoid,  and  arytenoid  cartilages 
(Fig.  145),  and  contains  the  vocal  cords,  by  the  vibration  of  which  the 
voice  is  chiefly  produced.  These  vocal  cords  are  ligamentous  bands  at- 
tached to  certain  cartilages  capable  of  movement  by  muscles.  By  their 
approximation  the  cords  can  entirely  close  the  entrance  into  the  larynx; 
but  under  the  ordinary  conditions,  the  entrance  of  the  larynx  is  formed 
by  a  more  or  less  triangular  chink  between  them,  called  the  rima  glot- 
tidis.  Projecting  at  an  acute  angle  between  the  base  of  the  tongue  and 
the  larynx  to  which  it  is  attached,  is  a  leaf-shaped  cartilage,  with  its 
larger  extremity  free,  called  the  epiglottis  (Fig.  145,  e).  The  whole  of  the 
larynx  is  lined  by  mucous  membrane,  which,  however,  is  extremely  thin 
over  the  cords.  At  its  lower  extremity  the  larynx  joins  the  trachea.  ^ 
With  the  exception  of  the  epiglottis  and  the  so-called  cornicula  laryngis, 
the  cartilages  of  the  larynx  are  of  the  hyaline  variety. 

Structure  of  Epiglottis. — The  supporting  cartilage  is  composed  of 
yellow  elastic  cartilage,  enclosed  in  a  fibrous  sheath  (perichondrium), 
and  covered  on  both  sides  with  mucous  membrane.  The  anterior  surface, 
which  looks  toward  the  base  of  the  tongue,  is  covered  with  mucous  mem- 
brane, the  basis  of  which  is  fibrous  tissue,  elevated  toward  both  surfaces  in 
the  form  of  rudimentary  papillae,  and  covered  with  several  layers  of 
squamous  epithelium.  In  it  ramify  capillary  blood-vessels,  and  in  its 
meshes  are  a  large  number  of  lymphatic  channels.  Under  the  mucous 
membrane,  in  the  less  dense  fibrous  tissue  of  which  it  is  composed,  are  a 
number  of  tubular  glands.  The  j)osterior  or  laryngeal  surface  of  the 
epiglottis  is  covered  by  a  mucous  membrane,  similar  in  structure  to  that 
on  the  other  surface,  but  that  the  epithelial  coat  is  thinner,  the  number 
of  strata  of  cells  being  less,  and  the  papillae  few  and  less  distinct.  The 
fibrous  tissue  which  constitutes  the  mucous  membrane  is  in  great  part  of 
the  adenoid  variety,  and  this  is  here  and  there  collected  into  distinct  masses 
or  follicles.  The  glands  of  the  posterior  surface  are  smaller  but  more 
numerous  than  those  on  the  other  surface.  In  many  places  the  glands 
wliicli  are  situated  nearest  to  the  perichondrium  are  directly  continuous 
through  apertures  in  the  cartilage  witli  those  on  the  other  side,  and  often 
the  ducts  of  the  glands  from  one  side  of  the  cartilage  pass  through  and 
open  on  tlie  mucous  surface  of  the  other  side,    l^fsfe  goblets  have  been 


'  A  dctaiUul  uccount  of  the  structure  and  function  of  the  Larynx  will  be  found  in 
Chapler  XVI. 


RESPIRATION. 


175 


found  in  the  epithelium  of  the  posterior  surface  of  the  epiglottis,  and  in 
several  other  situations  in  the  laryngeal  mucous  membrane. 

The  Trachea  and  Bronchial  Tubes.— The  trachea  or  wind-pipe 
extends  from  the  cricoid  cartilage,  which  is  on  a  level  with  the  fifth  cervi- 


FiG.  145.  Fig.  146. 

Fig.  145.— Outline  showing  the  general  form  of  the  larynx,  trachea,  and  bronchi,  as  seen  from 
"before,  the  great  cornu  of  the  hyoid  bone;  e,  epiglottis;  t,  superior,  and  inferior  cornu  of  the 
thyroid  cartilage;  c,  middle  of  the  cricoid  cartilage:  ti\  the  trachea,  showing  sixteen  cartilaginous 
rings;  ft,  the  right,  and  5',  the  left  bronchus.    (Allen  Thomson.)  X 

Fig.  146.— Outline  showing  the  general  form  of  the  larynx,  trachea,  and  bronchi,  as  seen  from  be- 
hind. 7i,  great  cornu  of  the  hyoid  bone;  ^,  superior,  and  t',  the  inferior  cornu  of  the  thyroid  cartilage; 
e,  the  epiglottis;  a,  points  to  the  back  of  both  the  arytenoid  cartilages  which  are  surmounted  by  the 
cornicula ;  c,  the  middle  ridge  on  the  back  of  the  cricoid  cartilage ;  ir,  the  posterior  membranous  part 
of  the  trachea;  6,  6',  right  and  left  bronchi.   (Allen  Thomson.)  ^. 

cal  vertebra,  to  a  point  opposite  the  third  dorsal  vertebra,  where  it  divides 
into  the  two  bronchi,  one  for  each  lung  (Fig.  146).  It  measures,  on  an 
average,  four  or  four-and-a-half  inches  in  length,  and  from  three-quarters 
of  an  inch  to  an  inch  in  diameter. 


176 


HAXD-BOOK  OF  PHYSIOLOGY. 


Structure. — Tlie  trachea  is  essentiall}"  a  tube  of  fibro-elastic  membrane, 
within  the  layers  of  which  are  enclosed  a  series  of  cartilaginous  rings,  from 
sixteen  to  twenty  in  number.  These  rings  extend  only  around  the  front 
and  sides  of  the  trachea  (about  two-thirds  of  its  circumference),  and  are 
deficient  behind;  the  interval  between  their  posterior  extremities  being 
bridged  over  by  a  continuation  of  the  fibrous  membrane  in  which  they 
are  enclosed  (Fig.  145).  The  cartilages  of  the  trachea  and  bronchial 
tubes  are  of  the  hyaline  variety. 


Fig  147.— Section  of  trachea,  a.  columnar  ciliated  epithelium:  h  and  c.  proper  structnre  of  the 
mucou.s  nembrane.  containing  elastic  fibres  cut  across  transversely;  rf.  subnuicous  tissue  contaiTiing 
mucous  glands,  e.  separated  from  the  hyaline  cartilage,  r/,  by  a  fine  fibrous  tissue,  /;  /i,  external  in- 
vestment of  fine  fibrous  tissue.   (S.  K.  Alcock.) 

Immediately  within  this  tube,  at  the  back,  is  "a  layer  of  unstriped 
muscular  fibres,  which  extends,  transverseh/,  l)etween  the  ends  of  the  car- 
tilaginous rings  to  whicli  tliey  are  attached,  and  opposite  the  intervals 
between  them,  also;  their  evident  function  being  to  diminish,  when  re- 
quired, the  calibre  of  the  trachea  by  approximating  the  ends  of  the  car- 
tilages. Outside  these  are  a  few  Jonfiitndinal  bundles  of  muscular  tissue 
which,  like  the  preceding,  are  attached  both  to  the  fibrous  and  cartilagi- 
nous framework. 


KESri  RATIO  >r. 


177 


The  mucous  membrane  consists  of  adenoid  tissue,  separated  from  the 
stratified  columnar  epithelium  which  lines  it  by  a  homogeneous  basement 
membrane.  This  is  penetrated  here  and  there  by  channels  which  connect 
the  adenoid  tissue  of  the  mucosa  with  the  intercellular  substance  of  the 
epithelium.  The  stratified  columnar  epithelium  is  formed  of  several 
layers  of  cells  (Fig.  147),  of  which  the  most  superficial  layer  is  ciliated, 
and  is  often  branched  downward  to  join  connective-tissue  corpuscles; 
while  between  these  branched  cells  are  smaller  elongated  cells  prolonged 
up  toward  the  surface  and  down  to  the  basement  membrane.  Beneath 
these  are  one  or  more  layers  of  more  irregularly  shaped  cells.  In  the 
deeper  part  of  the  mucosa  are  many  elastic  fibres  between  which  lie  con- 
nective-tissue corpuscles  and  capillary  blood-vessels. 

Numerous  mucous  glands  are  situate  on  the  exterior  and  in  the 
substance  of  the  fibrous  framework  of  the  trachea;  their  ducts  perfora- 
ting the  various  structures  which  form  the  wall  of  the  trachea,  and 
opening  through  the  mucous  membrane  into  the  interior. 

The  two  bronchi  into  which  the  trachea  divides,  of  which  the  right  is 
shorter,  broader,  and  more  horizontal  than  the  left  (Fig.  145),  resemble 
the  trachea  exactly  in  structure,  and  in  the  arrangement  of  their  carti- 
laginous rings.  On  entering  the  substance  of  the  lungs,  however,  the 
rings,  although  they  still  form  only  larger  or  smaller  segments  of  a  circle, 
are  no  longer  confined  to  the  front  and  sides  of  the  tubes,  but  are  dis- 
tributed impartially  to  all  parts  of  their  circumference. 

The  bronchi  divide  and  subdivide,  in  the  substance  of  the  lungs,  into 
a  number  of  smaller  and  smaller  branches,  which  penetrate  into  every 
part  of  the  organ,  until  at  length  they  end  in  the  smaller  subdivisions 
of  the  lungs,  called  lobules. 

All  the  larger  branches  still  have  walls  formed  of  tough  membrane, 
containing  portions  of  cartilaginous  rings,  by  which  they  are  held  open, 
and  unstriped  muscular  fibres,  as  well  as  longitudinal  bundles  of  elastic 
tissue.  They  are  lined  by  mucous  membrane,  the  surface  of  which,  like 
that  of  the  larynx  and  trachea,  is  covered  with  ciliated  epithelium  (Fig. 
148).  The  mucous  membrane  is  abundantly  provided  with  mucous 
glands. 

As  the  bronchi  become  smaller  and  smaller,  and  their  walls  thinner, 
the  cartilaginous  rings  become  scarcer  and  more  irregular,  until,  in  th& 
smaller  bronchial  tubes,  they  are  represented  only  by  minute  and  scattered 
cartilaginous  flakes.  And  when  the  bronchi,  by  successive  branches,  are 
reduced  to  about  -^^  of  an  inch  in  diameter,  they  lose  their  cartilaginous- 
element  altogether,  and  their  walls  are  formed  only  of  a  tough  fibrous, 
elastic  membrane,  with  circular  muscular  fibres;  they  are  still  lined,  how- 
ever, by  a  thin  mucous  membrane,  with  ciliated  epithelium.,  the  length  of 
the  cells  bearing  the  cilia  having  become  so  far  diminished,  that  the  cells 
are  now  almost  cubical.  In  the  smaller  bronchi  the  circular  muscular 
Vol.  I.— 10. 


178 


HAND-BOOK  OF  PHYSIOLOGY 


fibres  are  more  abundaiit  than  in  the  trachea  and  larger  bronchi,  and  form 
a  distinct  circular  coat. 

The  Lungs  and  Pleura. — The  Lungs  occupy  the  greater  portion  of 
the  thorax.  They  are  of  a  spongy  elastic  texture,  and  on  section  appear 
to  the  naked  eye  as  if  they  were  in  great  part  solid  organs,  except  here 
and  there,  at  certain  points,  where  branches  of  the  bronchi  or  air-tubes 
may  have  been  cut  across,  and  show,  on  the  surface  of  the  section,  their 


Fig.  148. — Transverse  section  of  a  bronchus,  about  one-fourth  of  an  inch  in  diameter,  e,  Epithe- 
lium (ciliated) ;  immediately  beneath  it  is  the  mucous  membrane  or  internal  fibrous  layer,  of  vari,-ing 
thickness;  m,  muscular  layer;  s,  m,  submucous  tissue;  /,  fibrous  tissue;  c,  cartilage  enclosed  within 
the  layers  of  fibrous  tissue;     mucous  gland.   (F.  E.  Schiilze.) 

tubular  structure.  In  fact,  however,  the  lungs  are  hollow  organs,  each 
of  which  communicates  by  a  separate  orifice  with  a  common  air-tube,  the 
trachea. 

The  Pleura, — Each  lung  is  enveloped  by  a  serous  membrane — the 
pleura,  one  layer  of  which  adheres  closely  to  the  surface  of  the  lung. 


1 !!».  — Transverse  section  of  the  chi>st  uvfter  Gray). 


and  provides  it  with  its  smooth  and  sli])i)ory  covering,  while  the  other 
adlnu-es  to  tlio  iimor  surfjuH'  of  the  chest-wall.  The  oontinnity  of  the 
two  layers,  which  form  m  ciostMl  sac,  as  in  the  case  of  oilier  serous  mom- 
brancs,  will  Ix^  l)t\s(  inuhM-siood  by  n^t'criMU'c  io  l^jg.  14'.).    The  ji]>poar;ince 


RESriRATION. 


179 


of  a  space,  however,  between  the  pleura  which  covers  the  lung  {visceral 
layer),  and  that  which  lines  the  inner  surface  of  the  chest  {parietal  layer), 
is  inserted  in  the  drawing  only  for  the  sake  of  distinctness.  These  layers 
are,  in  health,  everywhere  in  contact,  one  with  the  other;  and  between 
them  is  only  just  so  much  fluid  as  will  ensure  the  lungs  gliding  easily,  in 
their  expansion  and  contraction,  on  the  inner  surface  of  the  parietal 
layer,  which  lines  the  chest-wall.  While  considering  the  subject  of 
normal  respiration,  we  may  discard  altogether  the  notion  of  the  existence 
of  any  space  or  cavity  between  the  lungs  and  the  wall  of  the  chest. 

If,  however, '  an  opening  be  made  so  as  to  permit  air  or  fluid  to  enter 
the  pleural  sac,  the  lung,  in  virtue  of  its  elasticity,  recoils,  and  a  consid- 
erable space  is  left  between  the  lung  and  the  chest- wall.  In  other  words, 
the  natural  elasticity  of  the  lungs  would  cause  them  at  all  times  to  con- 
tract away  from  the  ribs,  were  it  not  that  the  contraction  is  resisted  by 
atmospheric  pressure  which  bears  only  on  the  inner  surface  of  the  air- 
tubes  and  air-cells.  On  the  admission  of  air  into  the  pleural  sac,  atmos- 
pheric pressure  bears  alike  on  the  inner  and  outer  surfaces  of  the  lung, 
and  their  elastic  recoil  is  thus  no  longer  prevented. 

Structure  of  the  Pleura  and  Lung. — The  pulmonary  pleura  consists 
of  an  outer  or  denser  layer  and  an  inner  looser  tissue.  The  former  or 
pleura  proper  consists  of  dense  fibrous  tissue  with  elastic  fibres,  covered 
by  endothelium,  the  cells  of  which  are  large,  flat,  hyaline,  and  transpar- 
ent when  the  lung  is  expanded,  but  become  smaller,  thicker,  and  gran- 
ular when  the  lung  collapses.  In  the  pleura  is  a  lymph-canalicular 
system;  and  connective  tissue  corpuscles  are  found  in  the  fibres  and  tissue 
which  forms  its  groundworr..  The  inner,  looser,  or  subpleural  tissue 
contains  lamellae  of  fibrous  connective  tissue  and  connective  tissue  cor- 
puscles between  them.  Numerous  lymphatics  are  to  be  met  with,  which 
form  a  dense  plexus  of  vessels,  many  of  which  contain  valves.  They  are 
simple  endothelial  tubes,  and  take  origin  in  the  lymph-canalicular  system 
of  the  pleura  proper.  Scattered  bundles  of  unstriped  muscular  fibre 
occur  in  the  pulmonary  pleura.  They  are  especially  strongly  developed 
on  those  parts  (anterior  and  internal  surfaces  of  lungs)  which  move  most 
freely  in  respiration:  their  function  is  doubtless  to  aid  in  expiration.  The 
structure  of  the  parietal  portion  of  the  pleura  is  very  similar  to  that  of 
the  visceral  layer. 

Each  lung  is  partially  subdivided  into  separate  portions  called  lohes; 
the  right  lung  into  three  lobes,  and  the  left  into  two.  Each  of  these 
lobes,  again,  is  composed  of  a  large  number  of  minute  parts,  called  lolules. 
Each  pulmonary  lobule  may  be  considered  a  lung  in  miniature,  consist- 
ing, as  it  does,  of  a  branch  of  the  bronchial  tube,  of  air-cells,  blood 
vessels,  nerves,  and  lymphatics,  with  a  sparing  amount  of  areolar 
tissue. 

On  entering  a  lobule,  the  small  bronchial  tube,  the  structure  of  which 


180  HAND-BOOK  OF  PHYSIOLOGY. 

has  been  just  described  {a,  Fig.  150),  divides  and  subdivides;  its  walls 
at  the  same  time  becoming  thinner  and  thinner,  until  at  length  they  are 
formed  only  of  a  thin  membrane  of  areolar  and  elastic  tissue,  lined  by  a 
layer  of  squamous  epithelium,  not  provided  with  cilia.  At  the  same 
time,  they  are  altered  in  shape;  each  of  the  minute  terminal  branches 


Fig.  150.— Ciliary  epitheliiim  of  the  human  trachea,  a,  Layer  of  longitudinally  arranged  elastic 
fibres;  &,  basement  membrane;  c,  deepest  ceUs,  circular  in  form;  d,  intermediate  elongated  cells;  e, 
outermost  layer  of  ceUs  fuUy  developed  and  bearing  ciUa.    x  350.  (Kolliker.) 

widening  out  funnel-wise,  and  its  walls  being  pouched  out  irregularly 
into  small  saccular  dilatations,  called  air-cells  (Fig.  151,  h).  Such  a. 
funnel-shaped  terminal  branch  of  the  bronchial  tube,  with  its  group  of 
pouches  or  air-cells,  has  been  called  an  mftindihulum  (Figs.  151,  152), 


Fig.  151.  Fig.  153. 

Fig,  151.— Terminal  branch  of  a  bronchial  tube,  with  its  infnndibiila  and  air-cells,  from  the  mar- 
gin of  the  lung  of  a  monkey,  injected  with  quicksilver,  a,  terminal  bronchial  twig;  b  6,  infundibula 
and  air-cells,  X  10.    (F.  Shulze.) 

Vm.  l.V-J.— Two  small  infimdibula  or  groups  of  air-cells,  a  o,  with  air-cells,  b  b,  and  the  ultimate 
bronchial  tubes,  c  c,  with  which  the  air-cells  comnmuicate.   From  a  ncw-boru  child.  (.Kiillikcr.) 

and  tlic  irregular  oblcmg  space  in  its  centre,  Avitli  which  tlio  air-cells  com- 
municate, an  intercellular  passage. 

The  air-cells,  or  air-vesicles,  may  be  placed  singly,  like  recesses  from 
tlu5  intorcelluhir  i)assage,  but  more  often  they  are  arranged  in  groups  or 


RESPIRATION. 


181 


even  in  rows,  like  minute  sacculated  tubes;  so  that  a  short  series  of 
vesicles,  all  communicating  with  one  another,  open  by  a  common  orifice 
into  the  tube.  The  vesicles  are  of  various  forms,  according  to  the  mutual 
pressure  to  which  they  are  subject;  their  walls  are  nearly  in  contact,  and 
they  vary  from  -^j^  to  of  an  inch  in  diameter.  Their  walls  are  formed 
of  fine  membrane,  similar  to  that  of  the  intercellular  passages,  and  con- 
tinuous with  it,  which  membrane  is  folded  on  itself  so  as  to  form  a  sharp- 
edged  border  at  each  circular  orifice  of  communication  between  con- 
tiguous air- vesicles,  or  between  the  vesicles  and  the  bronchial  passages. 
Numerous  fibres  of  elastic  tissue  are  spread  out  between  contiguous  air- 


Fig.  153. — From  a  section  of  lung  of  a  cat,  stained  with  silver  nitrate.  A.  D.  Alveolar  duct  or  in- 
tercellular passage.  S.  Alveolar  septa.  N.  Alveoli  or  air-ceUs,  lined  with  large  flat,  nucleated  Cells, 
with  some  smaller  polyhedral  nucleated  cells.  Circular  mviscular  fibres  are  seen  surrounding  the  in- 
terior of  the  alveolar  duct,  and  at  one  part  is  seen  a  group  of  small  polyhedral  ceUs  continued  from 
the  bronchus.   (Klein  and  Noble  Smith.) 

cells,  and  many  of  these  are  attached  to  the  outer  surface  of  the  fine 
membrane  of  which  each  cell  is  composed,  imparting  to  it  additional 
Strength,  and  the  power  of  recoil  after  distension.  The  cells  are  lined  by 
a  layer  of  epithelium  (Fig.  153),  not  provided  with  cilia.  Outside  the 
cells,  a  network  of  pulmonary  capillaries  is  spread  out  so  densely  (Fig. 
154),  that  the  interspaces  or  meshes  are  even  narrower  than  the  vessels, 
which  are,  on  an  average,  inch,  in  diameter.  .  Between  the 

atmospheric  air  in  the  cells  and  the  blood  in  these  vessels,  nothing  inter- 
venes but  the  thin  walls  of  the  cells  and  capillaries;  and  the  exposure  of 
the  blood  to  the  air  is  the  more  complete,  because  the  folds  of  membrane 
between  contiguous  cells,  and  often  the  spaces  between  the  walls  of  the 


182 


HAND-BOOK  OF  PHYSIOLOGY. 


same,  contain  only  a  single  layer  of  capillaries,  both  sides  of  which  are 
thus  at  once  exposed  to  the  air. 

The  air-vesicles  situated  nearest  to  the- centre  of  the  lung  are  smaller 
and  their  networks  of  capillaries  are  closer  than  those  nearer  to  the  cir- 
cumference. The  vesicles  of  adjacent  lobules  do  not  communicate;  and 
those  of  the  same  lobule  or  proceeding  from  the  same  intercellular  passage, 
do  so  as  a  general  rule  only  near  angles  of  bifurcation;  so  that,  when 
any  bronchial  tube  is  closed  or  obstructed,  the  supply  of  air  is  lost  for  all 
the  cells  opening  into  it  or  its  branches. 

Blood-supply. — The  lungs  receive  blood  from  two  sources,  {a)  the  pul- 
monary artery,  (b)  the  bronchial  arteries.  The  former  conveys  venous 
blood  to  the  lungs  for  its  arterialization,  and  this  blood  takes  no  share  in 
the  nutrition  of  the  pulmonary  tissues  through  which  it  passes,    {h)  The 


Fig.  154.— Capillary  network  of  the  pulmonary  blood-vessels  in  the  human  lung,  x  60.  (Kolliker.) 

branches  of  the  bronchial  arteries  ramify  for  nutrition's  sake  in  the  walls 
of  the  bronchi,  of  the  larger  pulmonary  vessels,  in  the  interlobular  con- 
nective tissue,  etc.;  the  blood  of  the  bronchial  vessels  being  returned 
chiefly  through  the  bronchial  and  partly  through  the  pulmonary  veins. 

Lymphatics. — The  lymphatics  are  arranged  in  three  sets: — 1.  Irreg- 
ular lacunae  in  the  walls  of  the  alveoli  or  air-cells.  Tlie  lymphatic  vessels 
Avhich  lead  from  these  accompany  tlic  i)ulmonary  vessels  toward  the  root 
of  the  lung.  2.  Irregular  anastomosing  s})aces  in  the  walls  of  the 
bronchi.  3.  Lymph-spaces  in  the  })ulmonary  pleura.  1'he  lymphatic 
vessels  from  all  these  irregular  sinuses  pass  in  toward  the  root  of  the  lung 
to  reach  tlio  ])r()n('lnal  glands. 

Nerves. — l^lie  lunwcs  of  the  lung  are  to  be  traced  from  the  anterior 
and  ])()sterior  pulmonary  ])lexuses,  which  are  formed  by  branches  of  the 
vagus  an<l  syni patlictic  M'he  nerves  follow  the  course  of  the  vessels  and 
bronchi,  and  in  the  walls  of  (lui  latter  many  small  ganglia  are  situated. 


RESPIRATION. 


183 


Mechanism  of  Respiration. 

Respiration  consists  of  the  alternate  expansion  and  contraction  of  the 
thorax,  by  means  of  which  air  is  drawn  into  or  expelled  from  the  lungs. 
These  acts  are  called  Inspiration  and  Expiration  respectively. 

For  the  inspiration  of  air  into  the  lungs  it  is  evident  that  all  that  is 
necessary  is  such  a  movement  of  the  side-walls  or  floor  of  the  chest,  or  of 
both,  that  the  capacity  of  the  interior  shall  be  enlarged.  By  such  in- 
crease of  capacity  there  will  be  of  course  a  diminution  of  the  pressure  of 
the  air  in  the  lungs,  and  a  fresh  quantity  will  enter  through  the  larynx  and 
trachea  to  equalize  the  pressure  on  the  inside  and  outside  of  the  chest. 

For  the  expiration  of  air,  on  the  other  hand,  it  is  also ,  evident  that, 
by  an  opposite  movement  which  shall  diminish  the  capacity  of  the  chest, 
the  pressure  in  the  interior  will  be  increased,  and  air  will  be  expelled, 
until  the  pressures  within  and  without  the  chest  are  again  equal.  In  both 
cases  the  air  passes  through  the  trachea  and  larynx,  whether  in  entering 
or  leaving  the  lungs,  there  being  no  other  communication  with  the  exterior 
of  the  body;  and  the  lung,  for  the  same  reason,  remains  under  all'  the 
circumstances  described  closely  in  contact  with  the  walls  and  floor  of  the 
chest.  To  speak  of  expansion  of  the  chest,  is  to  speak  also  of  expansion 
of  the  lung. 

We  have  now  to  consider  the  means  by  which  the  respiratory  move- 
ments are  effected. 

Respiratoey  Movements. 

A.  Inspiration. — The  enlargement  of  the  chest  in  inspiration  is  a 
muscular  act;  the  effect  of  the  action  of  the  inspiratory  muscles  being  an 
increase  in  the  size  of  the  chest-cavity  {a)  in  the  vertical,  and  {b)  in  the 
lateral  and  antero-posterior  diameters.  The  muscles  engaged  in  ordinary 
inspiration  are  the  diaphragm;  the  external  intercostals;  parts  of  the  in- 
ternal intercostals;  the  levatores  costarum;  and  serratus  posticus  superior. 

(a.)  The  vertical  diameter  of  the  chest  is  increased  by  the  contraction 
and  consequent  descent  of  the  diaphragm, — the  sides  of  the  muscle  de- 
scending most,  and  the  central  tendon  remaining  comparatively  unmoved; 
while  the  intercostal  and  other  muscles,  by  acting  at  the  same  time,  pre- 
vent the  diaphragm,  during  its  contraction,  from  drawing  in  the  sides 
of  the  chest. 

{h.)  The  increase  in  the  lateral  and  antero-posterior  diameters  of  the 
chest  is  effe(ited  by  the  raising  of  the  ribs,  the  greater  number  of  which 
are  attached  very  obliquely  to  the  spine  and  sternum  (see  Figure  of  Skele- 
ton in  frontispiece). 

The  elevation  of  the  ribs  takes  place  both  in  front  and  at  the  sides — 


\ 


184 


HAND-BOOK  OF  PHYSIOLOGY. 


the  hinder  ends  being  prevented  from  performing  any  upward  movement 
by  their  attachment  to  the  spine.  The  movement  of  the  front  extremities 
of  the  ribs  is  of  necessity  accompanied  by  an  upward  and  forward  move- 
ment of  the  sternum  to  which  they  are  attached,  the  movement  being 
greater  at  the  lower  end  than  at  the  upper  end  of  the  latter  bone. 


2i 


Fig.  155. — Diagram  of  axes  of  movement  of  ribs. 

The  axes  of  rotation  in  these  movements  are  two;  one  corresponding 
with  a  line  drawn  through  the  two  articulations-  which  the  rib  forms  with 
the  spine  (a  b,  Fig.  155);  and  the  other,  with  a  line  drawn  from  one  of 
these  (head  of  rib)  to  the  sternum  (A  B,  Fig.  155,  and  Fig.  156);  the 


Fio.  156.— Diagram  of  movement  of  a  rib  in  inspiration. 


motion  of  tlic  rib  around  the  latter  axis  being  somewhat  after  the  fashion 
of  raisiiiii;  tlio  handle  of  a  bucket. 

''I'lic  ('I(>va1i()n  of  the  ribs  is  accompanied  by  a  slight  opening  out  of  the 


RESPIRATION".  185 

angle  which  the  bony  part  forms  with  its  cartilage  (Fig.  156,  A);  and 
thus  an  additional  means  is  provided  for  increasing  the  antero-posterior 
diameter  of  the  chest. 

The  muscles  by  which  the  ribs  are  raised,  in  ordinary  quiet  inspiration, 
are  the  external  intercostals,  and  that  portion  of  the  internal  intercostals 
which  is  situate  between  the  costal  cartilages;  and  these  are  assisted  by 
the  levatores  costarum,  and  the  serratus  posticus  siq^erior.  The  action 
of  the  levatores  and  the  serratus  is  very  simple.  Their  fibres,  arising 
from  the  spine  as  a  fixed  point,  pass  obliquely  downward  and  forward  to 
the  ribs,  and  necessarily  raise  the  latter  when  they  contract.  The  action 
of  the  intercostal  muscles  is  not  quite  so  simple,  inasmuch  as,  passing 
merely  from  rib  to  rib,  they  seem  at  first  sight  to  have  no  fixed  point 
toward  which  they  can  pull  the  bones  to  which  they  are  attached. 

A  very  simple  apparatus  will  explain  this  apparent  anomaly  and  make 
their  action  plain.  Such  an  apparatus  is  shown  in  Fig.  157.  A  B  is  an 
upright  bar,  representing  the  spine,  with  which  are  jointed  two  parallel 
bars,  0  and  D,  which  represent  two  of  the  ribs,  and  are  connected  in 
front  by  movable  joints  with  another  upright,  representing  the  sternum. 


Fig.  157.  Fig.  158. 

Fig.  157.— Diagram  of  apparatus  showing  the  action  of  the  external  intercostal  muscles. 
Fig.  158.— Diagram  of  apparatus  showing  the  action  of  the  internal  intercostal  muscles. 


If  with  such  an  apparatus  elastic  bands  be  connected  in  imitation  of 
the  intercostal  muscles,  it  will  be  found  that  when  stretched  on  the  bars 
after  the  fashion  of  the  external  intercostal  fibres  (Fig.  157,  C  D),  i.e., 
passing  downward  and  forward,  they  raise  them  (Fig.  157,  C  D');  while 
on  the  other  hand,  if  placed  in  imitation  of  the  position  of  the  internal 
intercostals  (Fig.  158,  E  F),  i.e.,  passing  downward  and  backward,  they 
depress  them  (Fig.  158,  E'  F'). 

The  explanation  of  the  foregoing  facts  is  very  simple.  The  intercostal 
muscles,  in  contracting,  merely  do  that  which  all  other  contracting  fibres 


186 


HAND-BOOK  OF  PHYSIOLOGY. 


do,  viz.,  bring  nearer  together  the  points  to  which  they  are  attached; 
and  in  order  to  do  this,  the  external  intercostals  must  raise  the  ribs,  the 
points  C  and  D  (Fig.  15T)  being  nearer  to  each  other  when  the  parallel 
bars  are  in  the  position  of  the  dotted  lines.  The  limit  of  the  movement 
in  the  apparatus  is  reached  when  tlie  elastic  band  extends  at  right  angles 
to  the  two  bars  which  it  connects — the  points  of  attachment  C'  and  D' 
being  then  at  the  smallest  possible  distance  one  from  the  other. 

The  infernal  intercostals  (excepting  those  fibres  which  are  attached 
to  the  cartilages  of  the  ribs),  have  an  opposite  action  to  that  of  the  exter- 
nal. In  contracting  they  must  pull  down  the  ribs,  because  the  points  E 
and  F  (Fig.  158)  can  only  be  brought  nearer  one  to  another  (Fig.  158, 
E'  F')  by  such  an  alteration  in  their  position. 

On  account  of  the  oblique  position  of  the  cartilages  of  the  ribs  with 
reference  to  the  sternum,  the  action  of  the  tnfer-cartilaginous  fibres  of 
the  internal  intercostals  must,  of  course,  on  the  foregoing  principles,  re- 
semble that  of  the  external  intercostals. 

In  tranquil  breathing,  the  expansive  movements  of  the  lower  part  of 
the  chest  are  greater  than  those  of  the  upper.  In  forced  inspiration,  on 
the  other  hand,  the  greatest  extent  of  movement  appears  to  be  in  the 
upper  antero-j)osterior  diameter. 

Muscles  of  Extraordinary  Inspiration. — In  extraordinary  or 
forced  inspiration,  as  in  violent  exercise,  or  in  cases  in  Avhich  there  is 
some  interference  with  the  due  entrance  of  air  into  the  chest,  and  in 
which,  therefore,  strong  efforts  are  necessary,  other  muscles  than  those 
just  enumerated,  are  pressed  into  the  service.  It  is  very  difficult  or  im- 
possible to  separate  by  a  hard  and  fast  line,  the  so-called  muscles  of  ordi- 
nary from  those  of  extraordinary  inspiration;  but  there  is  no  doubt  that 
the  following  are  but  little  used  as  reBpiratory  agents,  except  in  cases  in 
which  unusual  efforts  are  required — the  scaleni  muscles,  the  sternomas- 
toid,  the  serratus  magnns,  the  pectorales,  and  the  trapezius.. 

Types  of  Respiration. — The  expansion  of  the  chest  in  inspiration 
presents  some  peculiarities  in  different  persons.  In  young  children,  it  is 
effected  chiefly  by  the  diaphragm,  which  being  highly  arched  in  expiration, 
becomes  flatter  as  it  contracts,  and,  descending,  presses  on  the  abdominal 
viscera,  and  pushes  forward  the  front  walls  of  the  abdomen.  The  move- 
ment of  the  abdominal  walls  being  here  more  manifest  than  that  of  any 
other  part,  it  is  usual  to  call  this  the  abdomuial  type  of  respiration.  In 
men,  together  with  the  descent  of  the  diaphragm,  and  the  pushing  for- 
Avard  of  the  front  wall  of  the  abdomen,  the  chest  and  the  sternum  are 
subject  to  a  wide  movement  in  inspiration  (inferior  costal  t3^pe).  In 
women,  the  movement  appears  less  extensive  in  tlie  lower,  and  more  so 
in  the  upper,  part  of  the  chest  (superior  costal  type).  (See  Figs.  159, 
IGO.) 

B.  Expiration. — From  tlie  enlargement  produced  in  inspiration, 
the  chest  and  lungs  return  in  ordinary  tranquil  expiration,  by  their  elas- 
ticity; the  force  enii)loyed  by  the  ins])irat()ry  muscles  in  distending  the 


EESPIRATION. 


187 


chest  and  overcoming  the  elastic  resistance  of  the  lungs  and  chest-walls, 
being  returned  as  an  expiratory  effort  when  the  muscles  are  relaxed. 
This  elastic  recoil  of  the  lungs  is  sufficient,  in  ordinary  quiet  breathing, 
to  expel  air  from  the  chest  in  the  intervals  of  inspiration,  and  no  muscular 
power  is  required.  In  all  voluntary  expiratory  efforts,  however,  as  in  speak- 
ing, singing,  blowing,  and  the  like,  and  in  many  involuntary  actions  also, 
as  sneezing,  coughing,  etc.,  something  more  than  merely  passive  elastic 
power  is  necessary,  and  the  proper  expiratory  muscles  are  brought  into 
action.    By  far  the  chief  of  these  are  the  abdominal  muscles,  which,  by 


Fig.  159.  Fig.  160, 


Fig.  159.— The  changes  of  the  thoracic  and  abdominal  walls  of  the  male  during  respiration.  The 
back  is  supposed  to  be  fixed,  in  order  to  throw  forward  the  respiratory  movement  as  much  as  possi- 
ble. The  outer  black  continuous  line  in  front  represents  the  ordinary  breathing  movement:  the  ante- 
rior margin  of  it  being  the  boundary  of  inspiration,  the  posterior  margin  the  limit  of  expiration.  The 
line  is  thicker  over  the  abdomen,  since  the  ordinary  respiratory  movement  is  chiefly  abdominal ;  thin 
over  the  chest,  for  there  is  less  movement  over  that  region.  The  dotted  line  indicates  the  movement 
on  deep  inspiration,  during  which  the  sternum  advances  while  the  abdomen  recedes. 

Fig.  160.— The  respiratory  movement  in  the  female.  The  lines  indicate  the  same  changes  as  in 
the  last  figure.  The  thickness  of  the  continuous  line  over  the  sternum  shows  the  larger  extent  of  the 
ordinary  breathing  movement  over  that  region  in  the  female  than  in  the  male.   (John  Hutchinson.) 

The  posterior  continuous  line  represents  in  both  figures  the  limit  of  forced  expiration. 

pressing  on  the  viscera  of  the  abdomen,  push  up  the  floor  of  the  chest 
formed  by  the  diaphragm,  and  by  thus  making  pressure  on  the  lungs, 
expel  air  from  them  through  the  trachea  and  larynx.  All  muscles,  how- 
ever, which  depress  the  ribs,  must  act  also  as  muscles  of  expiration,  and 
therefore  we  must  conclude  that  the  abdominal-  muscles  are  assisted  in 
their  action  by  the  greater  part  of  the  ivternal  intercostals,  the  triangu- 
laris sterni,  the  serratus  posticus  inferior,  and  qnadratus  lumhorum. 
When  by  the  efforts  of  the  expiratory  muscles,  the  chest  has  been  squeezed 
to  less  than  its  average  diameter,  it  again,  on  relaxation  of  the  muscles, 
returns  to  the  normal  dimensions  by  virtue  of  its  elasticity.    The  con- 


188 


HATO-BOOK  OF  PHYSIOLOGY. 


struction  of  the  chest- walls,  therefore,  admirably  adapts  them  for  recoiling 
against  and  resisting  as  well  undue  contraction  as  undue  dilatation. 

In  the  natural  condition  of  the  parts,  the  lungs  can  never  contract  to 
the  utmost,  but  are  always  more  or  less  ''on  the  stretch,^'  being  kept 
closely  in  contact  with  the  inner  surface  of  the  walls  of  the  chest  by 
atmospheric  pressure,  and  can  contract  away  from  these  only  when,  by 
some  means  or  other,  as  by  making  an  opening  into  the  pleural  cavity,  or 
by  the  effusion  of  fluid  there,  the  pressure  on  the  exterior  and  interior  of 
the  lungs  becomes  equal.  Thus,  under  ordinary  circumstances,  the 
degree  of  contraction  or  dilatation  of  the  lungs  is  dependent  on  that  of 
the  boundary  walls  of  the  chest,  the  outer  surface  of  the  one  being  in 
close  contact  with  the  inner  surface  of  the  other,  and  obliged  to  follow  it 
in  all  its  movements. 

Respiratory  Rhythm. — The  acts  of  expansion  and  contraction  of 
the  chest,  take  up,  under  ordinary  circumstances,  a  nearly  equal  time. 
The  act  of  inspiring  air,  however,  especially  in  women  and  children,  is  a 
little  shorter  than  that  of  expelling  it,  and  there  is  commonly  a  very 
slight  pause  between  the  end  of  expiration  and  the  beginning  of  the  next 
inspiration.    The  respiratory  rhythm  may  be  thus  expressed: — 

Inspiration  6 

Expiration  7  or  8 

A  very  slight  pause. 

Respiratory  Sounds. — If  the  ear  be  placed  in  contact  with  the  wall 
of  the  chest,  or  be  separated  from  it  only  by  a  good  conductor  of  sound, 
a  faint  respiratory  murmur  is  heard  during  inspiration.  This  sound 
varies  somewhat  in  different  parts — being  loudest  or  coarsest  in  the  neigh- 
borhood of  the  trachea  and  large  bronchi  (tracheal  and  bronchial  breath- 
ing), and  fading  off  into  a  faint  sighing  as  the  ear  is  placed  at  a  distance 
from  these  (vesicular  breathing).  It  is  best  heard  in  children,  and  in 
them  a  faint  murmur  is  heard  in  expiration  also.  The  cause  of  the  vesic- 
ular murmur  has  received  various  explanations.  Most  observers  hold 
that  the  sound  is  produced  by  the  friction  of  the  air  against  the  walls  of 
the  alveoli  of  the  lungs  when  they  are  undergoing  distension  (Laennec, 
Skoda),  others  that  it  is  due  to  an  oscillation  of  the  current  of  air  as  it 
enters  the  alveoli  (Ohauveau),  whilst  otliers  believe  that  the  sound  is  pro- 
duced in  the  glottis,  but  that  it  is  modified  in  its  passage  to  the  pulmo- 
]iary  alveoli  (Beau,  Geo). 

Respiratory  Movements  of  the  Nostrils  and  of  the  Glottis. — 
During  the  actioii  of  tlie  muscles  wliicli  directly  dr;iw  air  into  the  chest, 
those  wliicli  <^u;M'd  tlio  opening  through  wliich  it  enters  are  not  passive. 
In  liurried  ])i-cathing  tlie  instinctive  dilatation  of  the  nostrils  is  well  seen, 
although  under  ordinary  conditions  it  may  not  be  noticeable.  The  o])en- 
ing  at  the  upper  ])art  of  the  larynx,  howev(M-,  or  r\)na  (jJoitulix  (Fig.  ^5^7), 


RESPIRATION. 


189 


is  dilated  at  each  inspiration,  for  the  more  ready  passage  of  air,  and  be- 
comes smaller  at  each  expiration;  its  condition,  therefore,  corresponding 
during  respiration  with  that  of  the  walls  of  the  chest.  There  is  a  further 
likeness  between  the  f  wo  acts  in  that,  under  ordinary  circumstances,  the 
dilatation  of  the  rima  glottidis  is  a  muscular  act,  and  itc  contraction 
chiefly  an  elastic  recoil;  although,  under  various  conditions,  to  be  here- 
after mentioned,  there  may  be,  in  the  contraction  of  the  glottis,  consider- 
able muscular  power  exercised.  t-w  " 

Terms  used  to  express  Quantity  of  Air  breathed.— Breathing 
or  tidal  air,  is  the  quantity  of  air  which  is  habitually  and  almost  uni- 
formly changed  in  each  act  of  breathing.  In  a  healthy  adult  man  it  is 
about  30  cubic  inches. 

Complemental  air,  is  the  quantity  over  and  above  this  which  can  be 
drawn  into  the  lungs  in  the  deepest  inspiration;  its  amount  is  various,  as 
will  be  presently  shown. 

Reserve  air.  After  ordinary  expiration,  such  as  that  which  expels  the 
breathing  or  tidal  air,  a  certain  quantity  of  air  remains  in  the  lungs, 
which  may  be  expelled  by  a  forcible  and  deeper  expiration.  This  is 
termed  reserve  air. 

Residual  air  is  the  quantity  which  still  remains  in  the  lungs  after  the 
most  violent  expiratory  effort.  Its  amount  depends  in  great  measure  on 
the  absolute  size  of  the  chest,  but  may  be  estimated  at  about  100  cubic 
inches. 

The  total  quantity  of  air  which  passes  into  and  out  of  the  lungs  of  an 
adult,  at  rest,  in  24  hours,  is  about  686,000  cubic  inches.  This  quantity, 
however,  is  largely  increased  by  exertion;  the  average  amount  for  a  hard- 
working laborer  in  the  same  time,  being  1,568,390  cubic  inches. 

Respiratory  Capacity. — The  greatest  respiratory  capacity  of  the  chest 
is  indicated  by  the  quantity  of  air  which  a  person  can  expel  from  his  lungs 
by  a  forcible  expiration  after  the  deepest  inspiration  that  he  can  make; 
it  expresses  the  power  which  a  person  has  of  breathing  in  the  emergencies 
of  active  exercise,  violence,  and  disease.  The  average  capacity  of  an 
adult  (at  60°  F.  or  15-4°  C.)  is  about  225  cubic  inches. 

The  respiratory  capacity,  or  as  Hutchinson  called  it,  vital  capacity, 
is  usually  measured  by  a  modified  gasometer  {spirometer  of  Hutchinson), 
into  which  the  experimenter  breathes, — making  the  most  prolonged  ex- 
piration possible  after  the  deepest  possible  inspiration.  The  quantity  of 
air  which  is  thus  expelled  from  the  lungs  is  indicated  by  the  height  to 
which  the  air  chamber  of  the  spirometer  rises;  and  by  means  of  a  scale 
placed  in  connection  with  this,  the  number  of  cubic  inches  is  read  off. 

In  healthy  men,  the  respiratory  capacity  varies  chiefly  with  the  stature, 
weight,  and  age. 

It  was  found  by  Hutchinson,  from  whom  most  of  our  information  on 


190 


HAND-BOOK  OF  PHYSIOLOGY. 


this  subject  is  derived,  that  at  a  temperature  of  60°  F.,  225  cubic  inches 
is  the  average  vital  or  respiratory  capacity  of  a  healthy  person,  five  feet 
seven  inches  in  height 

Circumstances  affecting  the  amount  of  respiratory  capacity. — For 
every  inch  of  height  above  this  standard  the  capacity  is*^  increased,  on  an 
average,  by  eight  cubic  inches;  and  for  every  inch  below,  it  is  diminished 
by  the  same  amount. 

The  influence  of  weight  on  the  capacity  of  respiration  is  less  manifest 
and  considerable  than  that  of  height;  and  it  is  difficult  to  arrive  at  any 
definite  conclusions  on  this  point,  because  the  natural  average  weight  of 
a  healthy  man  in  relation  to  stature  has  not  yet  been  determined.  As  a 
general  statement,  however,  it  may  be  said  that  the  capacity  of  respiration 
is  not  affected  by  weights  under  161  pounds,  or  Hi  stones;  but  that, 
above  this  point,  it  is  diminished  at  the  rate  of  one  cubic  inch  for  every 
additional  pound  up  to  196  pounds,  or  14  stones. 

By  age,  the  capacity  appears  to  be  increased  from  about  the  fifteenth 
to  the  thirty-fifth  year,  at  the  rate  of  five  cubic  inches  per  year;  from 
thirty-five  to  sixty-five  it  diminishes  at  the  rate  of  about  one  and  a  half 
cubic  inch  per  year;  so  that  the  capacity  of  respiration  of  a  man  of  sixty 
years  old  would  be  about  30  cubic  inches  less  than  that  of  a  man  forty 
years  old,  of  the  same  height  and  weight.    (John  Hutchinson.) 

Number  of  Respirations,  and  Relation  to  the  Pulse. — The 

numler  of  respirations  in  a  healthy  adult  person  usually  ranges  from 
fourteen  to  eighteen  per  minute.  It  is  greater  in  infancy  and  childhood. 
It  varies  also  much  according  to  different  circumstances,  such  as  exercise 
or  rest,  health,  or  disease,  etc.  Variations  in  the  number  of  respirations 
correspond  ordinarily  with  similar  variations  in  the  pulsations  of  the 
heart.  In  health  the  proportion  is  about  1  to  4,  or  1  to  5,  and  when  the 
rapidity  of  the  hearths  action  is  increased,  that  of  the  chest  movement 
is  commonly  increased  also;  but  not  in  every  case  in  equal  proportion. 
It  happens  occasionally  in  disease,  especially  of  the  lungs  or  air-passages, 
that  the  number  of  respiratory  acts  increases  in  quicker  proportion  than 
the  beats  of  the  pulse;  and,  in  other  affections,  much  more  commonly, 
that  the  number  of  the  pulses  is  greater  in  proportion  tlian  that  of  the 
respirations. 

There  can  be  no  doubt  that  the  number  of  respirations  of  any  given 
animal  is  largely  affected  by  its  size.  Thus,  comparing  animals  of  the 
same  kind,  in  a  tiger  (lying  quietly)  the  number  of  respirations  was  20  per 
minute,  while  in  a  small  leopard  (lying  quietly)  the  number  was  30.  In 
a  small  monkey  40  per  ininnte;  in  a  large  baboon,  20. 

Tlie  rai)id,  panting  respiration  of  mice,  even  when  quite  still,  is 
familiar,  and  contrasts  strongly  with  the  slow  breathing  of  a  large  animal 
such  as  the  elephant  (eight  or  nine  times  per  minute).  These  facts  may 
be  explained  as  folloAvs: — '^l^he  heat-])roducing  power  of  any  given  animal 
depends  largely  on  its  bulk,  while  its  loss  of  heat  depends  to  a  great 
extent  upon  the  surface  area  of  its  body.  If  of  two  animals  of  similar 
shape,  one  be  ten  times  as  long  as  the  other,  the  area  of  the  large  animal 


RESPIRATION. 


(representing  its  loss  of  heat)  is  100  times  that  of  the  small  one,  while  its 
bulk  (representing  production  of  heat)  is  about  1000  times  as  great. 
Thus  in  order  to  balance  its  much  greater  relative  loss  of  heat,  the  smaller 
animal  must  have  all  its  vital  functions,  circulation,  respiration,  etc., 
carried  on  much  more  rapidly. 

Force  of  Inspiratory  and  Expiratory  Muscles. — The  force  with 
which  the  inspiratory  muscles  are  capable  of  acting  is  greatest  in  individ- 
uals of  the  height  of  from  five  feet  seven  inches  to  five  feet  eight  inches^ 
and  will  elevate  a  column  of  three  inches  of  mercury.  Above  this  height, 
the  force  decreases  as  the  stature  increases;  so  that  the  average  of  men 
of  six  feet  can  elevate  only  about  two  and  a  half  inches  of  mercury.  The 
force  manifested  in  the  strongest  expiratory  acts  is,  on  the  average,  one- 
third  greater  than  that  exercised  in  inspiration.  But  this  difference  is 
in  great  measure  due  to  the  power  exerted  by  the  elastic  reaction  of  the 
walls  of  the  chest;  and  it  is  also  much  influenced  by  the  disproportionate 
strength  which  the  expiratory  muscles  attain,  from  their  being  called  into 
use  for  other  purposes  than  that  of  simple  expiration.  The  force  of  the 
inspiratory  act  is,  therefore,  better  adapted  than  that  of  the  expiratory  for 
testing  the  muscular  strength  of  the  body.    (Jolin  Hutchinson.) 

The  instrument  used  by  Hutchinson  to  gauge  the  inspiratory  and  ex- 
piratory pow^r  was  a  mercurial  manometer,  to  which  was  attached  a  tube 
fitting  the  nostrils,  and  through  which  the  inspiratory  or  expiratory 
effort  was  made.  The  following  table  represents  the  results  of  numerous 
experiments: 


Power  of  Power  of 

Inspiratory  Muscles.  Expiratory  Muscles. 

1-  5  in   Weak      .       .       .    2*0  in. 

2-  0           .       .       .       .  Ordinary        .       .    2-5  " 
2-5           ....  Strong    .       .  .3-5 
3*5  "        ....  Very  strong     .       .    4*5  " 
4-5  "        .       .       .       .  Eemarkable    ,       .  5-8 
5'5           .       .       .       .  Very  remarkable     .  7-0" 

6-  0  .       .       •       .  Extraordinary        .  8-5 

7-  0  "        .       .       .     ..  Very  extraordinary  .  lO'O 


The  greater  part  of  the  force  exerted  in  deep  inspiration  is  employed 
in  overcoming  the  resistance  offered  by  the  elasticity  of  the  walls  of  the 
chest  and  of  the  lungs. 

The  amount  of  this  elastic  resistance  was  estimated  by  observing  the 
elevation  of  a  column  of  mercury  raised  by  the  return  of  air  forced,  after 
death,  into  the  lungs,  in  quantity  equal  to  the  known  capacity  of  respira- 
tion during  life;  and  Hutchinson  calculated,  according  to  the  well-known 
hydrostatic  law  of  equality  of  pressures  (as  shown  in  the  Bramah  press), 
that  the  total  force  to  be  overcome  by  the  muscles  in  the  act  of  inspiring 
200  cubic  inches  of  air  is  more  than  450  lbs. 


192 


HAND-BOOK  OF  PHYSIOLOGY. 


The  elastic  force  overcome  in  ordinary  inspiration  is,  according  to  the 
same  authority,  equal  to  about  170  lbs. 

Douglas  Powell  has  shown  that  within  the  limits  of  ordinary  tranquil 
respiration,  the  elastic  resilience  of  the  walls  of  the  chest  favors  inspira- 
tion; and  that  it  is  only  in  deep  inspiration  that  the  ribs  and  rib-cartilages 
offer  an  opposing  force  to  their  dilatation.  In  other  words,  the  elastic 
resilience  of  the  lungs,  at  the  end  of  an  act  of  ordinary  breathing,  has 
drawn  the  chest -walls  within  the  limits  of  their  normal  degree  of  expan- 
sion. Under  all  circumstances,  of  course,  the  elastic  tissue  of  the  lungs 
opposes  inspiration,  and  favors  expiration. 

Functions  of  Muscular  Tissue  of  Lungs. — It  is  possible  that  the 
contractile  power  which  the  bronchial  tubes  and  air-vesicles  possess,  by 
means  of  their  muscular  fibres  may  (1)  assist  in  expiration;  but  it  is  more 
likely  that  its  chief  purpose  is  (2)  to  regulate  and  adapt,  in  some  measure, 
the  quantity  of  air  admitted  to  the  lungs,  and  to  each  part  of  them, 
according  to  the  supply  of  blood;  (3)  the  muscular  tissue  contracts  upon 
and  gradually  expels  collections  of  mucus,  which  may  have  accumulated 
within  tiie  tubes,  and  cannot  be  ejected  by  forced  expiratory  efforts,  owing 
to  collapse  or  other  morbid  conditions  of  the  portion  of  lung  connected 
with  the  obstructed  tubes  (Gairdner).  (4)  Apart  from  any  of  the  before- 
mentioned  functions,  the  presence  of  muscular  fibre  in  the  walls  of  a  hol- 
low viscus,  such  as  a  lung,  is  only  what  might  be  expected  from  analogy 
with  other  organs.  Subject  as  the  lungs  are  to  such  great  variation  in 
size  it  might  be  anticipated  that  the  elastic  tissue,  which  enters  so  largely 
into  their  composition,  would  be  supplemented  by  the  presence  of  much 
muscular  fibre  also. 

Eespiratoey  Changes  in  the  Air  and  in  the  Blood. 
A.  In  the  Air. 

Compositioji  of  the  Atmosphere. — The  atmosphere  we  breathe  has,  in 
every  situation  in  which  it  has  been  examined  in  its  natural  state,  a  nearly 
uniform  composition.  It  is  a  mixture  of  oxygen,  nitrogen,  carbonic 
acid,  and  watery  vapor,  with,  commonly,  traces  of  other  gases,  as  ammonia, 
sulphuretted  hydrogen,  etc.  Of  every  100  volumes  of  pure  atmospheric 
air,  79  volumes  (on  an  average)  consist  of  nitrogen,  the  remaining  21  of 
oxygen.  By  weight  the  proportion  is  N.  75,  0.  25.  The  proportion  of 
carbonic  acid  is  extremely  small;  10,000  volumes  of  atmospheric  air  con- 
tain only  about  4  or  5  of  carbonic  acid. 

The  quantity  of  watery  vapor  varies  greatly  according  to  the  temper- 
ature and  other  circumstances,  but  the  atmospliere  is  never  without  some. 
In  this  country,  the  average  quantity  of  watery  vapor  in  the  atmosphere 
is  1  -40  })er  cent. 


KESPIRATIOW. 


193 


Composition  of  Air  which  has  heen  hreathed. — The  changes  effected  by 
respiration  in  the  atmospheric  air  are:  1,  an  increase  of  temperature;  2, 
an  increase  in  the  quantity  of  carbonic  acid;  3,  a  diminution  in  the  quan- 
tity of  oyxgen;  4,  a  diminution  of  volume;  5,  an  increase  in  the  amount 
of  watery  vapor;  Q,  the  addition  of  a  minute  amount  of  organic  matter 
and  of  free  ammonia. 

1.  The  expired  air,  heated  by  its  contact  with  the  interior  of  the 
lungs,  is  (at  least  in  most  climates)  hotter  than  the  inspired  air.  Its 
temperature  varies  between  97°  and  99.5°  F.  (36°— 37-5°  C),  the  lower 
temperature  being  observed  when  the  air  has  remained  but  a  short  time 
in  the  lungs.  Whatever  may  be  the  temperature  of  the  air  when  inhaled, 
it  nearly  acquires  that  of  the  blood  before  it  is  expelled  from  the  chest. 

2.  The  Carbonic  Acid  in  respired  air  is  always  increased;  but  the 
quantity  exhaled  in  a  given  time  is  subject  to  change  from  various  cir- 
cumstances. From  every  volume  of  air  inspired,  about  4*8  per  cent,  of 
oxygen  is  abstracted;  while  a  rather  smaller  quantity,  4 "3,  of  carbonic 
acid  is  added  in  its  place:  the  air  will  contain,  therefore,  434  vols,  of  car- 
bonic acid  in  10,000.  Under  ordinary  circumstances,  the  quantity  of 
carbonic  acid  exhaled  into  the  air  breathed  by  a  healthy  adult  man  amounts 
to  1346  cubic  inches,  or  about  636  grains  per  hour.  According  to  this  esti- 
mate, the  weight  of  carbon  excreted  from  the  lungs  is  about  173  grains 
per  hour,  or  rather  more  than  8  ounces  in  twenty-four  hours.  These 
quantities  must  be  considered  approximate  only,  inasmuch  as  various  cir- 
cumstances, even  in  health,  influence  the  amount  of  carbonic  acid  ex- 
creted, and,  correlatively,  the  amount  of  oxygen  absorbed. 

Circumstances  injluencing  the  amount  o  f  carbonic  acid  excreted, — The 
following  are  the  cifiief: — Age  and  sex.  Respiratory  movements.  Ex- 
ternal temperature.  Season  of  year.  Condition  of  respired  air.  Atmos- 
pheric conditions.  Period  of  the  day.  Food  and  drink.  Exercise  and 
sleep. 

a.  Age  and  Sex. — The  quantity  of  carbonic  acid  exhaled  into  the  air 
breathed  by  males,  regularly  increases  from  eight  to  thirty  years  of  age; 
from  thirty  to  fifty  the  quantity,  after  remaining  stationary  for  awhile, 
gradually  diminishes,  and  from  fifty  to  extreme  age  it  goes  on  diminish- 
ing, till  it  scarcely  exceeds  the  quantity  exhaled  at  ten  years  old.  In 
females  (in  whom  the  quantity  exhaled  is  always  less  than  in  males  of  the 
same  age)  the  same  regular  increase  in  quantity  goes  on  from  the  eighth, 
year  to  the  age  of  puberty,  when  the  quantity  abruptly  ceases  to  increase, 
and  remains  stationary  so  long  as  they  continue  to  menstruate.  When 
menstruation  has  ceased,  it  soon  decreases  at  the  same  rate  as  it  does  in 
old  men. 

h.  Respiratory  Movements. — The  more  quickly  the  movements  of 
respiration  are  performed,  the  smaller  is  the  proportionate  quantity  of 
carbonic  acid  contained  in  each  volume  of  the  expired  air.  Although, 
however,  the  proportionate  quantity  of  carbonic  acid  is  thus  diminished 
during  frequent  respiration,  yet  the  absolute  amount  exhaled  into  the  air 
within  a  given  time  is  increased  thereby,  owing  to  the  larger  quantity  of 
Vol.  I.— 13. 


194 


TTATO-BOOK  OF  PHYSIOLOGY. 


air  which  is  breathed  in  the  time.  The  last  half  of  a  volume  of  expired 
air  contains  more  carbonic  acid  than  the  half  first  exi)ired;  a  circumstance 
which  is  explained  by  the  one  portion  of  air  coming  from  the  remote  part 
of  the  lungs,  where  it  ]ias  been  in  more  immediate  and  prolonged  contact 
with  the  blood  than  the  other  has,  which  comes  chiefly  from  the  larger 
bronchial  tubes. 

c.  External  temjoerature. — The  observation  made  by  Vierordt  at  vari- 
ous temperatures  between  38"  F.  and  75°  F.  (3-4°— 23*8°  C.)  show,  for 
warm-blooded  animals,  that  within  this  range,  every  rise  equal  to  10°  F. 
causes  a  diminution  of  about  two  cubic  inches  in  the  quantity  of  carbonic 
acid  exhaled  per  minute. 

d.  Season  of  the  Year. — The  season  of  the  year,  independently  of 
temperature^  materially  influences  the  respiratory  phenomena;  spring  being 
the  season  of  the  greatest,  and  autumn  of  the  least  activity  of  the  res- 
piratory and  other  functions.    (Edward  Smith.) 

e.  Purity  of  the  Respired  Air. — The  average  quantity  of  carbonic  acid 
given  out  by  the  lungs  constitutes  about  4*3  per  cent,  of  the  expired 
air;  but  if  the  air  which  is  breathed  be  previously  impregnated  with  car- 
bonic acid  (as  is  the  case  when  the  same  air  is  frequently  respired),  then 
the  quantity  of  carbonic  acid  exhaled  becomes  much  less. 

/.  Hygrometric  State  of  Atmosphere. — The  amount  of  carbonic  acid 
exhaled  is  considerably  influenced  by  the  degree  of  moisture  of  the  atmos- 
phere, much  more  being  given  off  when  the  air  is  moist  than  when  it  is 
dry.  (Lehmann.) 

g.  Period  of  the  Day. — During  the  daytime  more  carbonic  acid  is  ex- 
haled than  corresponds  to  the  oxygen  absorbed;  while,  on  the  other  hand, 
at  night  very  much  more  oxygen  is  absorbed  than  is  exhaled  in  carbonic 
acid.  There  is,  thus,  a  reserve  fund  of.  oxygen  absorbed  by  night  to  meet 
the  requirements  of  the  day.  If  the  total  quantity  of  carbonic  acid  ex- 
haled in  24  hours  be  represented  by  100,  52  parts  are  exhaled  during  the 
day.  and  48  at  nigh't.  While,  similarly,  33  parts  of  the  oxygen  are  ab- 
sorbed during  the  dav,  and  the  remaining  67  by  night.  (Pettenkofer  and 
Voit.)  \ 

h.  Food  and  Drinlc. — By  the  use  of  food  the  quantity  is  increased, 
whilst  by  fasting  it  is  diminished;  it  is  greater  when  animals  are  fed  on 
farinaceous  food  than  when  fed  on  meat.  The  efi'ects  produced  by  spiritu- 
ous drinks  depend  much  on  the  kind  of  drink  taken.  Pure  alcohol  tends 
rather  to  increase  than  to  lessen  respiratory  changes,  and  the  amount 
therefore  of  carbonic  acid  expired;  rum,  ale.  and  porter,  also  sherry,  have 
very  similar  eft'ects.  On  the  other  hand,  brandy,  whisky,  and  gin,  par- 
ticularly the  latter,  almost  always  lessened  the  resj^iratory  changes,  and 
consequently  the  amount  of  carbonic  acid  exhaled.    (Edward  Smith.) 

i.  Exercise — Bodily  exercise,  in  moderation,  increases  the  quantity 
to  about  one-third  more  than  it  is  during  rest:  and  for  about  an  hour 
after  exercise  the  volume  of  the  air  expired  in  the  minute  is  increased 
about  118  cubic  inches:  and  the  quantity  of  carbonic  acid  about  7*8  cubic 
inches  per  minute.  Violent  exercise,  such  as  full  labor  on  the  treadwheel, 
still  further  increases  the  amount  of  the  acid  exhaled.    (Edward  Smith.) 

A  larger  quantity  is  exhaled  when  the  barometer  is  low  than  when  it 
is  high. 

3.  The  oxygen  is  diminished,  and  its  diminution  is  generally  propor- 
tionate to  the  increase  of  the  carbonic  acid. 


RESPIRATION". 


195 


For  every  volume  of  carbonic  acid  exhaled  into  the  air,  1*17421  volumes 
of  oxygen  are  absorbed  from  it,  and  134G  cubic  inches,  or  636  grains,  be- 
ing exhaled  in  the  hour,  the  quantity  of  oxygen  absorbed  in  the  same  time 
is  1584  cubic  inches,  or  542  grains.  According  to  this  estimate,  there  is 
more  oxygen  absorbed  than  is  exhaled  with  carbon  to  form  carbonic  acid. 

4.  The  volume  of  air  expired  in  a  given  time  is  less  than  that  of  the 
air  inspired  (allowance  being  made  for  the  expansion  in  being  heated), 
and  that  the  loss  is  due  to  a  portion  of  oxygen  absorbed  and  not  returned 
in  the  exhaled  carbonic  acid,  all  observers  agree,  though  as  to  the  actual 
quantity  of  oxygen  so  absorbed,  they  differ  even  widely.  The  amount  of 
oxygen  absorbed  is  on  an  average  4-8  per  cent.,  so  that  the  expired  air 
contains  10*2  volumes  per  cent,  of  that  gas. 

The  quantity  of  oxygen  that  does  not  combine  with  the  carbon  given 
off  in  carbonic  acid  from  the  lungs  is  probably  disposed  of  in  forming 
some  of  the  carbonic  acid  and  water  given  off  from  the  skin,  and  in  com- 
bining with  sulphur  and  phosphorus  to  form  part  of  the  acids  of  the  sul- 
phates and  phosphates  excreted  in  the  urine,  and  probably  also,  with  the 
nitrogen  of  the  decomposing  nitrogenous  tissues.    (Bence  Jones.) 

The  quantity  of  oxygen  in  the  atmosphere  surrounding  animals,  ap- 
pears to  have  very  little  influence  on  the  amount  of  this  gas  absorbed  by 
them,  for  the  quantity  consumed  is  not  greater  even  though  an  excess  of 
oxygen  be  added  to  the  atmosphere  experimented  with. 

It  has  often  been  discussed  whether  Nitrogen  is  absorbed  by  or  exhaled 
from  the  lungs  during  respiration.  At  present,  all,  that  can  be  said  on 
the  subject  is  that,  under  most  circumstances,  animals  appear  to  expire 
a  very  small  quantity  above  that  which  exists  in  the  inspired  air.  During 
prolonged  fasting,  on  the  contrary,  a  small  quantity  appears  to  be  ab- 
sorbed. 

5.  The  watery  vapor  is  increased.  The  quantity  emitted  is,  as  a  gen- 
eral rule,  sufficient  to  saturate  the  expired  air,  or  very  nearly  so.  Its  abso- 
lute amount  is,  therefore,  influenced  by  the  following  circumstances,  (1), 
by  the  quantity  of  air  respired;  for  the  greater  this  is,  the  greater  also 
will  be  the  quantity  of  moisture  exhaled.  (2),  by  the  quantity  of  watery 
vapor  contained  in  the  air  previous  to  its  being  inspired;  because  the 
greater  this  is,  the  less  will  be  the  amount  required  to  complete  the  satu- 
ration of  the  air;  (3),  by  the  temperature  of  the  expired  air;  for  the 
higher  this  is,  the  greater  will  be  the  quantity  of  watery  vapor  required 
to  saturate  the  air;  (4),  by  the  length  of  time  which  each  volume  of  in- 
spired air  is  allowed  to  remain  in  the  lungs;  for  although,  during  ordinary 
respiration,  the  expired  air  is  always  saturated  with  watery  vapor,  yet 
when  respiration  is  performed  very  rapidly  the  air  has  scarcely  time  to  be 
raised  to  the  highest  temperature,  or  be  fully  charged  with  moisture  ere 
it  is  expelled. 


196 


HAND-BOOK  OF  PHYSIOLOGY. 


The  quantity  of  water  exhaled  from  the  lungs  in  twenty-four  hours 
ranges  (according  to  the  various  modifying  circumstances  already  men- 
tioned) from  about  6  to  27  ounces,  the  ordinary  quantity  being  about  9 
or  10  ounces.  Some  of  this  is  probably  formed  by  the  chemical  combina- 
tion of  oxygen  with  hydrogen  in  the  system;  but  the  far  larger  propor- 
tion of  it  is  water  which  has  been  absorbed,  as  such,  into  the  blood  from 
the  alimentary  canal,  and  which  is  exhaled  from  the  surface  of  the  air- 
passages  and  cells,  as  it  is  from  the  free  surfaces  of  all  moist  animal  mem- 
branes, particularly  at  the  high  temperature  of  warm-blooded  animals. 

6.  A  small  quantity  of  ammonia  is  added  to  the  ordinary  constituents 
of  expired  air.  It  seems  probable,  however,  both  from  the  fact  that  this 
substance  cannot  be  always  detected,  and  from  its  minute  amount  when 
present,  that  the  whole  of  it  may  be  derived  from  decomposing  particles 
of  food  left  in  the  mouth,  or  from  carious  teeth  or  the  like;  and  that  it 
is,  therefore,  only  an  accidental  constituent  of  expired  air. 

7.  The  quantity  of  organic  matter  in  the  breath  is  about  3  grains  in 
twenty -four  hours.  (Ransome.) 

The  following  represents  the  kind  of  experiment  by  which  the  fore- 
going facts  regarding  the  excretion  of  carbonic  acid,  water,  and  organic 
matter,  have  been  established. 

A  bird  or  mouse  is  placed  in  a  large  bottle,  through  the  stopper  of 
which  two  tubes  pass,  one  to  supply  fresh  air,  and  the  other  to  carry  oft 
that  which  has  been  expired.  Before  entering  the  bottle,  the  air  is 
made  to  bubble  through  a  strong  solution  of  caustic  potash,  which  absorbs 
the  carbonic  acid,  and  then  through  lime-water,  which  by  remaining 
limpid,  proves  the  absence  of  carbonic  acid.  The  air  which  has  been 
breathed  by  the  animal  is  made  to  bubble  through  lime  water,  which  at 
once  becomes  turbid  and  soon  quite  milky  from  the  precipitation  of  cal- 
cium carbonate;  and  it  finally  passes  through  strong  sulphuric  acid, 
which,  by  turning  brown,  indicates  the  presence  of  organic  matter.  The 
watery  vapor  in  the  expired  air  will  condense  inside  the  bottle  if  the  sur- 
face be  kept  cool. 

By  means  of  an  apparatus  sufficiently  large  and  well  constructed, 
experiments  of  the  kind  have  been  made  extensively  on  man. 

Methods  by  which  the  Respiratory  Changes  in"  the  Air  are 

effected. 

The  method  by  which  fresh  air  is  inhaled  and  expelled  from  the  lungs 
has  been  considered.  It  remains  to  consider  liow  it  is  that  the  blood 
absorbs  oxygen  from,  and  gives  up  carbonic  acid  to,  tlio  air  of  the  alveoli. 
In  the  first  place,  it  must  be  remembered  that  the  tidal  air  only  amounts 
to  about  25 — 30  cubic  inches  at  each  inspiration,  and  that  this  is  of  course 
insufficient  to  fill  the  lungs,  but  it  mixes  with  the  stationary  air  by  diffx- 
si(m,  and  so  supplies  to  it  now  oxygon.  Tlio  amount  of  oxygen  in  ox])irod 
air,  wliicli  may  be  taken  as  tlio  average  composition  of  the  mixed  air  in 


RESPIRATION. 


197 


the  lungs,  is  about  16  to  17 per  cent.;  in  the  pulmonary  alveoli  it  may  be 
rather  less  than  this.  From  this  air  the  venous  blood  has  to  take  up  0x3'- 
gen  in  the  proportion  of  8  to  12  vols,  in  every  hundred  volumes  of  blood, 
as  the  difference  between  the  amount  of  oxygen  in  arterial  and  venous 
blood  is  no  less  than  that.  It  seems  therefore  somewhat  difficult  to  un- 
derstand how  this  can  be  accomplished  at  the  low  oxygen  tension  of  the 
pulmonary  air.  But  as  was  pointed  out  in  a  previous  Chapter  (IV.),  the 
oxygen  is  not  simply  dissolved  in  the  blood,  but  is  to  a  great  extent 
chemically  combined  with  the  haemoglobin  of  the  red  corpuscles;  and  when 
a  fluid  contains  a  body  which  enters  into  loose  chemical  combination  in 
this  way  with  a  gas,  the  tension  of  the  gas  in  the  fluid  is  not  directly  pro- 
portional to  the  total  quantity  of  the  gas  taken  up  by  the  fluid,  but  to  the 
excess  above  the  total  quantity  which  the  substance  dissolved  in  the  fluid 
is  capable  of  taking  up  (a  known  quantity  in  the  case  of  haemoglobin, 
viz.,  1*59  cm.  for  one  grm.  haemoglobin).  On  the  other  hand,  if  the  sub- 
stance be  not  saturated,  i.e.,  if  it  be  not  combined  with  as  much  of  the 
gas  as  it  is  capable  of  taking  up,  further  combination  leads  to  no  increase 
of  its  tension.  However,  there  is  a  point  at  which  the  haemoglobin  gives 
up  its  oxygen  when  it  is  exposed  to  a  low  partial  pressure  of  oxygen,  and 
there  is  also  a  point  at  which  it  neither  takes  up  nor  gives  out  oxygen; 
in  the  case  of  arterial  blood  of  the  dog,  this  is  found  to  be  when  the  oxy- 
gen tension  of  the  atmosphere  is  equal  to  3*9  per  cent,  (or  29-6  mm.  of 
mercury),  which  is  equivalent  to  saying  that  the  oxygen  tension  of  arterial 
blood  is  3  '9  per  cent. ;  venous  blood,  in  a  similar  manner,  has  been  found 
to  have  an  oxygen  tension  of  2*8  per  cent.  At  a  higher  temperature,  the 
tension  is  raised,  as  there  is  a  greater  tendency  at  a  high  temperature  for 
the  chemical  compound  to  undergo  dissociation.  It  is  therefore  easy  to 
see  that  the  oxygen  tension  of  the  air  of  the  pulmonary  alveoli  is  quite 
sufficient,  even  supposing  it  much  less  than  that  of  the  expired  air,  to 
enable  the  venous  blood  to  take  up  oxygen,  and  what  is  more,  it  will  take 
it  up  until  the  haemoglobin  is  very  nearly  saturated  with  the  gas. 

As  regards  the  elimination  of  carbonic  acid  from  the  blood,  there  is 
evidence  to  show  that  it  is  given  up  by  a  process  of  simple  diffusion,  the 
only  condition  necessary  for  the  process  being  that  the  tension  of  the  car- 
bonic acid  of  the  air  in  the  pulmonary  alveoli  should  be  less  than  the  ten- 
sion of  the  carbonic  acid  in  venous  blood.  The  carbonic  acid  tension  of 
the  alveolar  air  probably  does  not  exceed  in  the  dog  3  or  4  per  cent., 
while  that  of  the  venous  blood  is  5*4  per  cent.,  or  equal  to  41  mm.  of 
mercury. 

B.  Respiratory  Changes  in  the  Blood. 

Circulation  of  Blood  in  the  Respiratory  Organs. — To  be  ex- 
posed to  the  air  thus  alternately  moved  into  and  out  of  the  air  cells  and 
minute  bronchial  tubes,  the  blood  is  propelled  from  the  right  ventricle 


198 


HAND-BOOK  OF  PHYSIOLOGY. 


through  the  pulmonary  capillaries  in  steady  streams,  and  slowly  enough 
to  permit  every  minute  portion  of  it  to  be  for  a  few  seconds  exposed  to 
the  air,  with  only  the  thin  walls  of  the  capillary  vessels  and  the  air-cells 
intervening.  The  pulmonary  circulation  is  of  the  simplest  kind:  for  the 
pulmonary  artery  branches  regularly;  its  successive  branches  run  in 
straight  lines,  and  do  not  anastomose:  the  capillary  plexus  is  uniformly 
spread  over  the  air-cells  and  intercellular  passages;  and  the  veins  derived 
from  it  proceed  in  a  course  as  simple  and  uniform  as  that  of  the  arteries, 
their  branches-  converging  but  not  anastomosing.  The  veins  have  no 
valves,  or  only  small  imperfect  ones  prolonged  from  their  angles  of  junc- 
tion, and  incapable  of  closing  the  orifice  of  either  of  the  veins  between 
which  they  are  placed.  The  pulmonary  circulation  also  is  unaffected  by 
changes  of  atmospheric  pressure,  and  is  not  exposed  to  the  influence  of 
the  pressure  of  muscles:  the  force  by  which  it  is  accomplished,  and  the 
course  of  the  blood,  are  alike  simple. 

Changes  produced  in  the  Blood  by  Respiration. — The  most 
obvious  change  which  the  blood  of  the  pulmonary  artery  undergoes  in 
its  passage  through  the  lungs  is  1^^,  that  of  color,  the  dark  crimson  of 
venous  blood  being  exchanged  for  the  bright  scarlet  of  arterial  blood;  'ind, 
and  in  connection  with  the  preceding  change,  it  gains  oxygen;  3r^?,  it 
loses  carbonic  acid;  Uhy  it  becomes  slightly  cooler  (p.  193);  bih,  it  coagu- 
lates sooner  and  more  firmly,  and,  apparently,  contains  more  fibrin  (see 
p.  87).  The  oxygen  absorbed  into  the  blood  from  the  atmospheric  air 
in  the  lungs  is  combined  chemically  with  the  hsemoglobin  of  the  red 
blood-corpuscles.  In  this  condition  it  is  carried  in  the  arterial  blood  to 
the  various  parts  of  the  body,  and  brought  into  near  relation  or  contact 
with  the  tissues.  In  these  tissues,  and  in  the  blood  which  circulates  in 
them,  a  certain  portion  of  the  oxygen,  which  the  arterial  blood  contains, 
disappears,  and  a  proportionate  quantity  of  carbonic  acid  and  water  is 
formed.  The  venous  blood,  containing  the  new-formed  carbonic  acid, 
returns  to  the  lungs,  where  a  portion  of  the  carbonic  acid  is  exhaled,  and 
a  fresh  supply  of  oxygen  is  taken  in. 

Mechanism  of  Various  Respiratory  Actions. — It  will  be  well 
here,  perhaps,  to  explain  some  respiratory  acts,  which  appear  at  first 
sight  somewhat  complicated,  but  cease  to  be  so  when  the  mechanism  by 
which  they  are  performed  is  clearly  understood.  The  accompanying  dia- 
gram (Fig.  IGl)  shows  that  the  cavity  of  the  chest  is  separated  from  that 
of  the  abdomen  by  the  diaphragm,  which,  when  acting,  will  lessen  its 
curve,  and  thus  descending,  will  push  downward  and  forward  the  ab- 
dominal viscera;  while  the  abdominal  muscles  have  the  opposite  effect, 
and  in  actiiig  will  push  tlie  viscera  vpward  and  hacl-ward,  and  with 
them  the  diaphragm,  supposing  its  ascent  to  be  not  from  any  clause  inter- 
fered with.  From  the  same  diagram  it  will  be  seen  that  the  lungs  com- 
municate with  the  exterior  of  the  body  through  the  glottis,  and  further 


KESPIRATION. 


199 


on  through  the  month  and  nostrils — through  either  of  them  separately, 
or  through  both  at  the  same  time,  according  to  the  position  of  the  soft 
palate.  The  stomach  communicates  with  the  exterior  of  the  body  through 
the  oesophagus,  pharynx,  and  mouth;  while  below  the  rectum  opens  at 
the  anus,  and  the  bladder  through  the  urethra.  All  these  openings, 
through  which  the  hollow  viscera  communicate  with  the  exterior  of  the 
body,  are  guarded  by  muscles,  called  sphincters,  which  can  act  independ- 
ently of  each  other.  The  position  of  the  latter  is  indicated  in  the  dia- 
gram. 


Fig.  161. 


Sighing. — In  sighing  there  is  a  rather  prolonged  inspiration;  the  air 
almost  noiselessly  passing  in  through  the  glottis,  and  by  the  elastic  recoil 
of  the  lungs  and  chest -walls,  and  probably  also  of  the  abdominal  walls, 
being  rather  suddenly  expelled  again. 

Now,  in  the  first,  or  inspiratory  part  of  this  act,  the  descent  of  the 
diaphragm  presses  the  abdominal  yiscera  dowuAvard,  and.  of  course  this 
pressure  tends  to  evacuate  the  contents  of  such  as  communicate  with  the 
exterior  of  the  body.  Inasmuch,  however,  as  their  various  openings  are 
guarded  by  sphincter  muscles,  in  a  state  of  constant  tonic  contraction. 


200  HAND-BOOK  OF  PHYSIOLOGY. 

there  is  no  escape  of  their  contents,  and  air  simply  enters  the  lungs.  In 
the  second,  or  expiratory  part  of  the  act  of  sighing,  there  is  also  pressure 
made  on  the  abdominal  viscera  in  the  opposite  direction,  by  the  elastic 
or  muscular  recoil  of  the  abdominal  walls;  but  the  pressure  is  relieved  by 
the  escape  of  air  through  the  open  glottis,  and  the  relaxed  diaphragm  is 
pushed  up  again  into  its  original  position.  The  sphincters  of  the  stomach, 
rectum,  and  bladder,  act  as  before. 

Hiccough  resembles  sighing  in  that  it  is  an  inspiratory  act;  but  the 
inspiration  is  sudden  instead  of  gradual,  from  the  diaphragm  acting  sud- 
denly and  spasmodically;  and  the  air,  therefore,  suddenly  rushing  through 
the  unprepared  rima  glottidis,  causes  vibration  of  the  vocal  cords,  and 
the  peculiar  sound. 

Coughing. — In  the  act  of  coughing,  there  is  most  often  first  an  in- 
spiration, and  this  is  followed  by  an  expiration;  but  when  the  lungs  have 
been  filled  by  the  preliminary  inspiration,  instead  of  the  air  being  easily 
let  out  again  through  the  glottis,  the  latter  is  momentarily  closed  by  the 
approximation  of  the  vocal  cords,  and  then  the  abdominal  muscles, 
strongly  acting,  push  up  the  viscera  against  the  diaphragm,  and  thus 
make  pressure  on  the  air  in  the  lungs  until  its  tension  is  sufficient  to 
burst  open  noisily  the  vocal  cords  which  oppose  its  outward  passage.  In 
this  way  a  considerable  force  is  exercised,  and  mucus  or  any  other  matter 
that  may  need  expulsion  from  the  lungs  or  trachea  is  quickly  and  sharply 
expelled  by  the  outstreaming  current  of  air. 

Kow  it  is  evident  on  reference  to  the"  diagram  (Fig.  161),  that  pressure 
exercised  by  the  abdominal  muscles  in  the  act  of  coughing,  acts  as  for- 
cibly on  the  abdominal  viscera  as  on  the  lungs,  inasmuch  as  the  viscera 
form  the  medium  by  which  the  upward  pressure  on  the  diaphragm  is 
made,  and  of  necessity  there  is  quite  as  great  a  tendency  to  the  expulsion 
of  their  contents  as  of  the  air  in  the  lungs.  The  instinctive,  and  if 
necessary,  voluhtarily  increased  contraction  of  the  sphincters,  howevei", 
prevents  any  escape  at  the  opepnings  guarded  by  them,  and  the  pressure  is 
effective  at  one  part  only,  namely,  the  rima  glottidis. 

Sneezing. — The  same  remarks  that  apply  to  coughing,  are  almost 
exactly  applicable  to  the  act  of  "sneezing;  but  in  this  instance  the  blast 
of  air,  on  escaping  from  the  lungs,  is  directed,  by  an  instinctive  con- 
•traction  of  the  pillars  of  the  fauces  and  descent  of  the  soft  palate,  chiefly 
through  the  nose,  and  any  offending  matter  is  thence  expelled. 

Speaking. — In  speaking,  there  is  a  voluntary  expulsion  of  air  through 
(lie  glottis  by  means  of  the  expiratory  mu?cles;  and  the  vocal  cords  are 
])ut,  ])y  the  muscles  of  the  larynx,  in  a  proper  position  and  state  of  tension 
for  vibrating  as  tlie  air  passes  over  them,  and  thus  producing  sound.  The 
sound  is  moulded  into  words  by  the  tongue,  teeth,  lips,  etc. — the  vocal 
cords  prodiuiing  the  sound  only,  and  having  nothing  to  do  with  articu- 
lation. 


RESPIRATION. 


201 


Singing. — Singing  resembles  speaking  in  the  manner  of  its  produc- 
tion; the  laryngeal  muscles,  by  variously  altering  the  position  and  degree 
of  tension  of  the  vocal  cords,  producing  the  different  notes.  Words  used 
in  the  act  of  singing  are  of  course  framed,  as  in  speaking,  by  the  tongue, 
teeth,  lips,  etc. 

Sniffing. — Sniffing  is  produced  by  a  somewhat  quick  action  of  the 
diaphragm  and  other  inspiratory  muscles.  The  mouth  is,  however,  closed, 
and  by  these  means  the  whole  stream  of  air  is  made  to  enter  by  the 
nostrils.  The  alae  nasi  are,  commonly,  at  the  same  time,  instinctively 
dilated. 

Sobbing. — Sobbing  consists  in  a  series  of  convulsive  inspirations,  at 
the  moment  of  which  the  glottis  is  usually  more  or  less  closed. 

Laughing. — Laughing  is  a  series  of  short  and  rapid  expirations. 

Yawning. — Yawning  is  an  act  of  inspiration,  but  is  unlike  most  of  the 
preceding  actions  in  being  always  more  or  less  involuntary.  It  is  attended 
by  a  stretching  of  various  muscles  about  the  palate  and  lower  jaw,  which 
is  probably  analogous  to  the  stretching  of  the  muscles  of  the  limbs  in 
whicli  a  weary  man  finds  relief,  as  a  voluntary  act,  when  they  have  been 
some  time  out  of  action.  The  involuntary  and  reflex  character  of  yawn- 
ing depends  probably  on  the  fact  that  the  muscles  concerned  are  them- 
selves at  all  times  more  or  less  involuntary,  and  require,  therefore, 
something  beyond  the  exercise  of  the  will  to  set  them  in  action.  For 
the  same  reason,  yawning,  like  sneezing,  cannot  be  well  performed 
voluntarily. 

Sucking. — Sucking  is  not  properly  a  respiratory  act,  but  it  may  be 
most  conveniently  considered  in  this  place.  It  is  caused  chiefly  by  the 
depressor  muscles  of  the  os  hyoides.  These,  by  drawing  downward  and 
backward  the  tongue  and  floor  of  the  mouth,  produce  a  partial  vacuum 
in  the  latter:  and  the  weight  of  the  atmosphere  then  acting^ i;)n  all  sides 
tends  to  prod^uce  equilibrium  on  the  inside  and  outsid^ 
best  it  may.  The  communication  betweefn  the  moui 
completely  shut  off  by  the  contraction  of  the  pillars  offfhe  sofjb^palate' 
descent  of  the  latter  so  as  to  touch  the  back  of  the  toi 
librium,  therefore,  can  be  restored  only  by  the  entr^V-e^  of  sO^^^thfng 
through  the  mouth.  The  action,  indeed,  of  the  tongur 
mouth  in  sucking  may  be  compared  to  that  of  the 
and  the  muscles  which  pull  down  the  os  hyoides  and  tongue^'^l^^^h^  power 
which  draws  the  handle. 

Influence  of  the  Nervous  System  in  Respiration.- 
other  functions  of  the  body,  the  discharge  of  which  is  necessary  to  life, 
respiration  must  be  essentially  an  involuntary  act.  Else,  life  would  be  in 
constant  danger,  and  would  cease  on  the  loss  of  consciousness  for  a  few 
moments,  as  in  sleep.  But  it  is  also  necessary  that  respiration  should  be 
to  some  extent  under  the  control  of  the  will.    For  were  it  not  so,  it  would 


202 


HAND-BOOK  OF  PHYSIOLOGY. 


be  impossible  to  perform  those  voluntary  respiratory  acts  which  have  been 
just  enumerated  and  explained,  as  speaking,  singing,  and  the  like. 

The  respiratory  movements  and  their  rhythm^  so  far  as  they  are  invol- 
untary and  independent  of  consciousness  (as  on  all  ordinary  occasions)  are 
under  the  governance  of  a  nerve-centre  in  the  medulla  oblongata  correspond- 
ing with  the  origin  of  the  pneumogastric  nerves;  that  is  to  say,  the  motor 
nerves^  and  through  them  the  muscles  concerned  in  the  respiratory  move- 
ments, are  excited  by  a  stimulus  which  issues  from  this  part  of  the  nerv- 
ous system.  How  far  the  medulla  acts  automatically,  i.e.,  how  far  the 
stimulus  originates  in  it,  or  how  far  it  is  merely  a  nerve-centre  for  reflex 
action,  is  not  certainly  known.  Probably,  as  will  be  seen,  both  events 
happen;  and,  in  both  cases,  the  stimulus  is  the  result  of  the  condition  of 
the  blood. 

The  respiratory  centre  is  bilateral  or  double,  since  the  respiratory 
movements  continue  after  the  medulla  at  this  point  is  divided  in  the  mid- 
dle line. 

As  regards  its  supposed  automatic  action,  it  has  been  shown  that  if 
the  spinal  cord  be  divided  below  the  medulla,  and  both  vagi  be  divided 
so  that  no  afferent  impulses  can  reach  it  from  below,  the  nasal  and  laryn- 
geal respiration  continues,  and  the  only  possible  course  of  the  afferent  im- 
pulses would  be  through  the  cranial  nerves;  and  when  the  cord  and  me- 
dulla are  intact  the  division  of  these  produces  no  effect  upon  respiration, 
so  that  it  appears  evident  that  the  afferent  stimuli  are  not  absolutely 
necessary  for  maintaining  the  respiratory  movements.  But  although  au- 
tomatic in  its  action  the  respiratory  centre  may  be  reflexly  excited,  and  the 
chief  channel  of  this  reflex  influence  is  the  vagus  nerve;  for  when  the 
nerve  of  one  side  is  divided,  respiration  is  slowed,  and  if  both  vagi  be  cut 
the  respiratory  action  is  still  slower. 

The  influence  of  the  vagus  trunk  upon  it  is  twofold,  for  if  the  nerve 
be  divided  below  the  origin  of  the  superior  laryngeal  branch  and  the  cen- 
tral end  be  stimulated,  respiratory  movements  are  increased  in  rapidity, 
and  indeed  follow  one  another  so  quickly  if  the  stimuli  be  increased  in 
number,  that  after  a  time  cessation  of  respiration  in  inspiration  follows 
from  a  tetanus  of  the  respiratory  muscles  (diaphragm).  Whereas  if  the 
superior  laryngeal  branch  be  divided,  although  no  effect,  or  scarcely  any, 
follows  the  mere  division,  on  stimulation  of  the  central  end  respiration 
is  slowed,  and  after  a  time,  if  the  stimulus  be  increased,  stops,  but  not  in 
inspiration  as  in  the  other  case,  but  in  expiration.  Thus  the  vagus  trunk 
contains  fibres  which  slow  and  fibres  which  accelerate  respiration.  If  we 
adopt  the  theory  of  a  doubly  acting  respiratory  centre  in  the  floor  of  the 
medulla,  one  tending  to  produce  inspiration  and  the  other  expiration, 
and  acting  in  antagonism  as  it  were,  so  that  there  is  a  gradual  increase  in 
tlie  tendency  to  produce  respiratory  action,  until  it  culminates  in  an  in- 
spiratory effort,  wliich  is  followed  by  a  similar  action  of  the  expiratory 


RESPIRATION. 


203 


part  of  the  centre,  producing  an  expiration,  we  must  look  upon  the  main 
trunk  of  the  vagus  as  aiding  the  inspiratory,  and  of  the  superior  laryngeal 
as  aiding  the  expiratory  part  of  the  centre,  the  first  nerve  possibly  in- 
hibiting the  action  of  the  expiratory  centre,  whilst  it  aids  the  inspiratory, 
and  the  latter  nerve  having  the  very  opposite  effect.  But  inasmuch  as 
the  respiration  is  slowed  on  division  of  the  vagi,  and  not  quickened  or 
affected  manifestly  on  simple  division  of  the  superior  laryngeal,  it  must 
be  supposed  that  the  vagi  fibres  are  always  in  action,  whereas  the  superior 
laryngeal  fibres  are  not. 

It  appears,  however,  that  there  are,  in  some  animals  at  all  events, 
subordinate  centres  in  the  spinal  cord  which  are  able,  under  certain  con- 
ditions, to  discharge  the  function  of  the  chief  medullary  centre. 

The  centre  in  the  medulla  may  be  influenced  not  only  by  afferent  im- 
pulses proceeding  along  the  vagus  and  laryngeal  nerves  but  also  by  those 
proceeding  from  the  cerebrum,  as  well  as  by  impressions  made  upon  the 
nerves  of  the  skin,  or  upon  part  of  the  fifth  nerve  distributed  to  the  nasal 
mucous  membrane,  or  upon  other  sensory  nerves,  as  is  exemplified  by 
the  deep  inspiration  which  follows  the  application  of  cold  to  the  surface 
of  the  skin,  and  by  the  sneezing  which  follows  the  slightest  irritation  of 
the  nasal  mucous  membrane. 

At  the  time  of  birth,  the  separation  of  the  placenta,  and  the  conse- 
quent non-oxygenation  of  the  foetal  blood,  are  the  circumstances  which 
immediately  lead  to  the  issue  of  automatic  impulses  to  action  from  the 
respiratory  centre  in  the  medulla  oblongata.  But  the  quickened  action 
which  ensues  on  the  application  of  cold  air  or  water,  or  other  sudden 
stimulus,  to  the  skin,  shows  well  the  intimate  connection  which  exists 
between  this  centre  and  other  parts  which  are  not  ordinarily  connected 
with  the  function  of  respiration. 

Methods  of  Stimulation  of  the  Respiratory  Centre.— It  is  now 

necessary  to  consider  the  method  by  which  the  centre  or  centres  are  stim- 
ulated themselves,  as  well  as  the  manner  in  which  the  afferent  vagi 
impulses  are  produced. 

The  more  venous  the  blood,  the  more  marked  are  the  inspiratory  im- 
pulses, and  if  the  air  is  prevented  from  entering  the  chest,  in  a  short  time 
the  respiration  becomes  very  labored.  Its  cessation  is  followed  by  an 
abnormal  rapidity  of  the  inspiratory  acts,  which  make  up  even  in  depth 
for  the  previous  stoppage.  The  condition  caused  by  obstruction  to  the 
entrance  of  air,  or  by  any  circumstance  by  which  the  oxygen  of  the  blood 
is  used  up  in  an  abnormally  quick  manner,  is  known  as  dyspyioea,  and  as 
the  aeration  of  the  blood  becomes  more  and  more  interfered  with,  not 
only  are  the  ordinary  respiratory  muscles  employed,  but  also  those  extra- 
ordinary muscles  which  have  been  previously  enumerated  (p.  186),  so  that 
as  the  blood  becomes  more  and  more  venous  the  action  of  the  medullary 
centre  becomes  more  and  more  active.    The  question  arises  as  to  what 


204 


HAND-BOOK  OF  PHYSIOLOGY. 


condition  of  the  venous  bbod  causes  this  increased  activity,  whether  it 
is  due  to  deficiency  of  oxygen  or  excess  of  carbonic  acid  in  the  blood. 
This  has  been  answered  by  the  experiments,  which  show  on  the  one  hand 
that  dyspnoea  occurs  when  there  is  no  obstruction  to  the  exit  of  carbonic 
acid,  as  when  an  animal  is  placed  in  an  atmosphere  of  nitrogen,  and 
therefore  cannot  be  due  to  the  accumulation  of  carbonic  acid,  and  sec- 
ondly, that  if  plenty  of  oxygen  be  supplied,  dyspnoea  proper  does  not 
occur,  although  the  carbonic  acid  of  the  blood  is  in  excess.  The  respir- 
atory centre  is  evidently  stimulated  to  action  by  the  absence  of  sufficient 
oxygen  in  the  blood  circulating  in  it. 

The  method  by  which  the  vagus  is  stimulated  to  conduct  afferent  im- 
pulses, influencing  the  action  of  the  respiratory  centre,  appears  to  be  by 
the  venous  blood  circulating  in  the  lungs,  or  as  some  say  by  the  condition 
of  the  air  in  the  pulmonary  alveoli.  And  if  either  of  these  be  the  stimuli 
it  Avill  be  evident  that  as  the  condition  of  venous  blood  stimulates  the 
peripheral  endings  of  the  vagus  in  the  lungs,  the  vagus  action  which  tends 
to  help  on  the  discharge  of  inspiratory  impulses  from  the  centre,  must 
tend  also  to  increase  the  activity  of  the  centre,  Avhen  the  blood  in  the 
lungs  becomes  more  and  more  venous.  Xo  doubt  the  venous  condition 
of  the  blood  will  affect  all  the  sensory  nerves  in  a  similar  manner,  but  it 
has  been  shown  that  the  circulation  of  too  little  blood  through  the 
centre  is  quite  sufficient  by  itself  for  the  purpose;  as  when  its  blood  sup- 
ply is  cut  off  increased  inspiratory  actions  ensue. 

Effects  of  Vitiated  Air. — Ventilation. — T\^e  have  seen  that  the 
air  expired  from  the  lungs  contains  a  large  proportion  of  carbonic  acid 
and  a  minute  amount  of  organic  putrescible  matter. 

Hence  it  is  obvious  that  if  the  same  air  be  breathed  again  and  again, 
the  proportion  of  carbonic  acid  and  organic  matter  will  constantly  increase 
till  fatal  results  are  produced;  but  long  before  this  point  is  reached, 
uneasy  sensations  occur,  such  as  headache,  languor,  and  a  sense  of  oppres- 
sion. It  is  a  remarkable  fact  that  the  organism  after  a  time  adapts  itself 
to  such  a  vitiated  atmosphere,  and  that  a  person  soon  comes  to  breathe, 
without  sensible  inconvenience,  an  atuiosphere  which,  when  he  first 
entered  it,  felt  intolerable.  Such  an  adaptation,  however,  can  only  take 
]"»lare  at  the  expense  of  a  depression  of  all  the  vital  functions,  which  must 
be  injurious  if  long  continued  or  often  repeated. 

This  power  of  adaptation  is  well  illustrated  by  the  experiments  of 
Claude  Bernard.  A  sparrow  is  placed  under  a  bell-glass  of  such  a  size 
that  it  will  live  for  three  hours.  If  now  at  the  end  of  the  second  hour 
(when  it  could  have  survived  another  liour)  it  be  taken  out  and  a  fresh 
healthy  sj)arrow  introduced,  the  latter  will  ]HM'ish  instantly. 

The  ada])tation  above  spoken  of  is  a  gradual  and  continuous  one:  thus 
a  bird  which  will  live  one  hour  in  ii  })int  of  air  will  live  three  hours  in 
two  pints;  and  it!  two  birds  of  the  same  species,  age,  and  size,  be  placed 


RESPIRATION. 


205 


in  a  quantity  of  air  in  which  either,  separately,  would  survive  thrco 
hours,  they  will  not  live  I  j-  hour,  but  only  11  hour. 

From  what  has  been  said  it  must  be  evident  that  provision  for  a  con- 
stant and  plentiful  supply  of  fresh  air,  and  the  removal  of  that  which  is 
vitiated,  is  of  far  greater  importance  than  the  actual  cubic  space  per  head 
of  occupants.  Not  less  than  2000  cubic  feet  per  head  should  be  allowed 
in  sleeping  apartments  (barracks,  hospitals,  etc.),  and  with  this  allow- 
ance the  air  can  only  be  maintained  at  the  proper  standard  of  purity  by 
such  a  system  of  ventilation  as  provides  for  the  supply  of  1500  to  2000 
cubic  feet  of  fresh  air  per  head  per  hour.  (Parkes.) 

The  Effect  of  Respiratiok  on  the  Cieculatiok. 

Inasmuch  as  the  heart  and  great  vessels  are  situated  in  the  air-tight 
thorax,  they  are  exposed  to  a  certain  alteration  of  pressure  when  the 


Fi<5.  162.— Diagram  of  an  apparatus  illustrating  the  effect  of  inspiration  upon  the  heart  and  great 
vessek  within  the  thorax. — I,  the  thorax  at  rest;  II,  during  inspiration;  d,  represents  the  diaphragm 
when  relaxed;  d'  when  contracted  (it  must  be  remembered  that  this  position  is  a  mere  diagram),  i.  e., 
when  the  capacity  of  the  thorax  is  enlarged;  h,  the  heart;  v,  the  veins  entering  it,  and  a,  the  aorta; 
rI,  U,  the  right  and  left  lung;  t,  the  trachea;  m,  mercurial  manometer  in  connection  with  the  pleura. 
The  increase  in  the  capacity  of  the  box  representing  the  thorax  is  seen  to  dilate  the  heart  as  well  as 
the  lungs,  and  so  to  pump  in  blood  through  v,  whereas  the  valve  prevents  reflex  through  a.  The 
position  of  the  mercury  in  m  shows  also  the  suction  which  is  taking  place.  (Landois.) 

capacity  of  the  latter  is  inc?'eased;  for  although  the  expansion  of  the 
lungs  during  inspiration  tends  to  counterbalance  this  increase  of  area,  it 
never  quite  does  so,  since  part  of  the  pressure  of  the  air  which  is  drawn 


206 


HAND-BOOK  OF  PHYSIOLOGY. 


into  the  cliest  tlirongli  the  trachea  is  expended  in  overcoming  the  elas- 
ticity of  the  Inngs  themselves.  The  amount  thus  used  up  increases  as 
the  lungs  become  more  and  more  expanded,  so  that  the  pressure  inside 
the  thorax  during  inspiration  as  far  as  the  heart  and  great  vessels  are  con- 
cerned, never  quite  equals  that  outside,  and  at  the  conclusion  of  inspira- 
tion is  considerably  less  than  the  atmospheric  pressure.  It  has  been  ascer- 
tained that  the  amount  of  the  pressure  used  up  in  the  way  above  described, 
varies  from  5  or  7  mm.  of  mercury  during  the  pause,  and  to  30  mm.  of 
mercury  when  the  lungs  are  expanded  at  the  end  of  a  deep  inspiration, 
so  that  it  will  be  understood  that  the  pressure  to  which  the  heart  and 
great  vessels  are  subjected  diminishes  as  inspiration  progresses.  It  will 
be  understood  from  the  accompanying  diagram  how,  if  there  were  no 
lungs  in  the  chest,  but  if  its  capacity  were  increased,  the  effect  of  the 
increase  would  be  expended  in  pumping  blood  into  the  heart  from  the 
veins,  but  even  Avith  the  lungs  placed  as  they  are,  during  inspiration  the 
f)ressure  outside  the  heart  and  great  vessels  is  diminished,  and  they  have 
therefore  a  tendency  to  expand  and  to  diminish  the  intra-vascular  pres- 
sure. The  diminution  of  pressure  within  the  veins  passing  to  the  right 
auricle  and  within  the  right  auricle  itself,  will  draw  the  blood  into  the 
thorax,  and  so  assist  the  circulation:  this  suction  action  aiding,  though 
independently,  the  suction  power  of  the  diastole  of  the  auricle  about 
which  we  have  previously  spoken  (p.  124).  The  effect  of  sucking  more 
blood  into  the  right  auricle  will,  cceteris  parihus,  increase  the  amount 
passing  through  the  right  ventricle,  which  also  exerts  a  similar  suction 
action,  and  through  the  lungs  into  the  left  auricle  and  ventricle  and  thus 
into  the  aorta,  and  this  tends  to  increase  the  arterial  tension.  The  effect 
of  the  diminished  pressure  upon  the  pulmonary  vessels  will  also  help 
toward  the  same  end,  i.e.,  an  increased  flow  through  the  lungs,  so  that  as 
far  as  the  heart  and  its  veins  are  concerned  inspiration  increases  the  blood 
pressure  in  the  arteries.  The  effect  of  inspiration  upon  the  aorta  and  its 
branches  within  the  thorax  would  be,  however,  contrary;  for  as  the 
pressure  outside  is  diminished  the  vessels  would  tend  to  expand,  and  thus 
to  diminish  the  tension  of  the  blood  within  them,  but  inasmuch  as  the 
large  arteries  are  capable  of  little  expansion  beyond  their  natural  calibre, 
the  diminution  of  the  arterial  tension  caused  by  this  means  would  be  in- 
sufficient to  counteract  the  increase  of  arterial  tension  produced  by  the 
effect  of  inspiration  upon  the  veins  of  the  chest,  and  the  balance  of  the 
whole  action  would  be  in  favor  of  an  increase  of  arterial  tension  during 
the  ins2)iratory  period,  l^ut  if  a  tracing  of  the  variation  be  taken  at  the 
same  time  that  the  respiratory  movements  are  recorded,  it  will  be  found 
tliat,  although  speaking  generally,  the  arterial  tension  is  increased  during 
inspiration,  the  nuiximum  of  arterial  tension  does  not  correspond  with 
the  acme  of  inspiration  (Fig.  liV.V). 

As  regards  the  ctTect  of  ex]uration,  tlun^apacity  of  the  clu^st  is  dimin- 


RESPIRATION. 


207 


ished,  and  the  intra-thoracic  prossiu'o  returns  to  tlie  normal,  which  is 
not  exactly  equal  to  the  atmospheric,  pressure.  The  effect  of  this  on  the 
veins  is  to  increase  their  intra-vascular  pressure,  and  so  to  diminish  the 
flow  of  blood  into  the  left  side  of  tlie  heart,  and  with  it  the  arterial  ten- 
sion, but  this  is  almost  exactly  balanced  by  the  necessary  increase  of 
arterial  tension  caused  by  the  increase  of  the  extra-vascular  pressure  of 
the  aorta  and  large  arteries,  so  that  the  arterial  tension  is  not  much 
affected  during  expiration  either  way.    Thus,  ordinary  expiration  does 


( 

i 

- 

K 

■ 

■\ 

b 

a 

1 

,■ 

\r\AA 

y  ■ . 

1  '"■.-'■■-■^ 

■  ■■•  .V 

Fig.  163.— Comparison  of  blood-pressure  curve  with  curve  of  intra-thoracic  pressure.  (To  be  read 
from  left  to  right.)  a  is  a  curve  of  olood-pressure  with  its  respiratory  undulations,  the  slower  beats 
on  the  descent  being  very  marked;  6  is  the  curve  of  intra-thoracic  pressure  obtained  by  connecting 
one  Umb  of  a  manometer  with  the  pleural  cavity.  Inspiration  begins  at  i  and  expiration  at  e.  The 
intra-thoracic  pressure  rises  very  rapidly  after  the  cessation  of  the  inspiratory  effort,  and  then  slow- 
ly falls  as  the  air  issues  from  the  chest;  at  the  beginning  of  the  inspiratory  effort  the  fall  becomes 
more  rapid.   (M.  Foster.) 

not  produce  a  distinct  obstruction  to  the  circulation,  as  even  when  the 
expiration  is  at  an  end  the  intra-thoracic  pressure  is  less  than  the  extra- 
thoracic. 

The  effect  of  violent  expiratory  efforts,  however,  has  a  distinct  action 
in  preventing  the  current  of  blood  through  the  lungs,  as  seen  in  the 
blueness  of  the  face  from  congestion  in  straining;  this  condition  being 
produced  by  pressure  on  the  small  pulmonary  vessels. 

We  may  summarize  this  mechanical  effect,  therefore,  and  say  that  in- 
spiration aids  the  circulation  and  so  increases  the  arterial  tension,  and 
that  although  expiration  does  not  materially  aid  the  circulation,  yet  under 
ordinary  conditions  neither  does  it  obstruct.  Under  extraordinary  con- 
ditions, as  in  violent  expirations,  the  circulation  is  decidedly  obstructed. 
But  we  have  seen  that  there  is  no  exact  correspondence  between  the 
points  of  extreme  arterial  tension  and  the  end  of  inspiration,  and  we  must 
look  to  the  nervous  system  for  an  explanation  of  this  apparently  contra- 
dictory result. 

The  effect  of  the.  nervous  system  in  producing  a  rhythmical  alteration 
of  the  blood  pressure  is  twofold.  In  the  first  place  the  cardio-inJiihitory 
centre  is  believed  to  be  stimulated  during  the  fall  of  blood  pressure,  pro- 


208 


HAND-BOOK  OF  PHYSIOLOGY. 


ducing  a  slower  rate  of  heart-beats  during  expiration,  which  will  be 
noticed  in  the  tracing  (Fig.  163),  the  undulations  during  the  decline  of 
blood-pressure  being  longer  but  less  frequent.  This  effect  disappears 
when,  by  section  of  the  vagi,  the  eifect  of  the  centre  is  cut  off  from  the 
heart.  In  the  second  place,  the  vaso-motor  centre  is  also  believed  to  send 
out  rhythmical  impulses,  by  which  undulations  of  blood  pressure  are  pro- 
duced independently  of  the  mechanical  effects  of  respiration. 


Fig.  164.— Traube-Hering's  curves.  (To  be  read  from  left  to  right.)  The  curves  1,  2,  3,  4,  and  5 
are  portions  selected  from  one  continuous  tracing  forming  the  record  of  a  prolonged  observation,  so 
that  the  several  curves  represent  successive  stages  of  the  same  expei-iment.  Each  cm-ve  is  placed  in 
its  proper  position  relative  to  the  base  Hne,  which  is  omitted;  the  blood-pressure  rises  in  stages  from 
1,  to  2,  3,  and  4,  but  falls  again  in  stage  .5.  Curve  1  is  taken  from  a  period  when  artificial  respiration 
was  being  kept  up,  but  the  vagi  having  been  divided,  tlie  pulsations  on  the  ascent  and  descent  of  the 
undulations  do  not  differ;  when  artificial  resiTiratioii  ceased  these  undula!  ions  for  a  while  disappeared, 
and  the  blood-pressure  rose  steadily  while  the  heart-beats  heeanie  slo^\  (^r.  SQon,  as  at  0.  new  un- 
dulations apjK'ared;  a  little  later,  tlie,  blood-pressun"  was  st.ill  i-isin;;-.  the  heart-beats  still  slower,  hut 
the  undulations  still  more  obvious  (3):  still  later  (4),  the  pi-essure  was  still  higher,  hut  the  heart-heatvS 
were  (iuic;ker,  and  the  undulations  fiatter,  tlie  i)ressure  tluni  Im  gan  to  fall  rapidly-  (,6),  and  continued 
to  fall  until  some  time  after  artificial  respiration  was  resumed.    (IM.  Foster.) 


The  action  of  the  vaso-motor  centre  in  taking  part  in  producing 
rhythmical  changes  of  blood-pressure  which  are  called  respiratory,  is 
shown  in  the  following  way: — In  an  animal  under  the  influence  of  imiri, 
record  of  whose  blood -pressure  is  being  taken,  and  where  artificial  respi- 
ration has  been  st()])ped,  and  botli  vagi  cut,  the  blood-pressure  curve  rises 
at  first  jilmost  in  a  sf  raiglit  line;  but  jiftiM-  a  lime  iumv  rhythmical  undula- 
tions occur  very  like  llir  original  res])irat()ry  undulations,  only  somewhat 


I 


RESPIRATION. 


209 


larger.  These  are  called  Traitles  or  Trauhe-Hering's  curves.  They  con- 
tinue whilst  the  blood-pressure  continues  to  rise,  and  only  cease  when  the 
vaso-motor  centre  and  the  heart  are  exhausted,  when  the  pressure  speedily 
falls.  These  curves  must  be  dependent  upon  the  vaso-motor  centre,  as 
the  mechanical  effects  of  respiration  have  been  eliminated  by  the  poison 
and  by  the  cessation  of  artificial  respiration,  and  the  effect  of  the  cardio- 
inhibitory  centre  be  the  division  of  the  vagi.  It  may  be  presumed  there- 
fore that  the  vaso-motor  centre,  as  well  as  the  cardio-inhibitory,  must  be 
considered  to  take  part  with  the  mechanical  changes  of  inspiration  and 
expiration  in  producing  the  so-called  respiratory  undulations  of  blood- 
pressure. 

Cheyne-8tohes's  'breathing. — This  is  a  rhythmical  irregularity  in  respi- 
rations which  has  been  observed  in  various  diseases,  and  is  especially  con- 
nected with  fatty  degeneration  of  the  heart.  Eespirations  occur  in  groups, 
at  the  beginning  of  each  group  the  inspirations  are  very  shallow,  but  each 
successive  breath  is  deeper  than  the  preceding  until  a  climax  is  reached, 
then  comes  in  a  prolonged  sighing  expiration,  succeeded  by  a  pause,  after 
which  the  next  group  begins. 

Apkcea. — Dyspkcea. — Asphyxia. 

As  blood  which  contains  a  normal  proportion  of  oxygen  excites  the 
respiratory  centre  (p.  204),  and  as  the  excitement  and  consequent  respir- 
atory muscular  movements  are  greater  (dyspnoea)  in  proportion  to  the 
deficiency  of  this  gas,  so  an  abnormally  large  proportion  of  oxygen  in  the 
blood  leads  to  diminished  breathing  movements,  and,  if  the  proportion  be 
large  enough,  to  their  temporary  cessation.  This  condition  of  absence  of 
breathing  is  termed  apnoea,"-  and  it  can  be  demonstrated,  in  one  of  the 
lower  animals,  by  performing  artificial  respiration  to  the  extent  of  satura- 
ting the  blood  with  oxygen. 

When,  on  the  other  hand,  the  respiration  is  stopped,  by,  e.g., 
interference  with  the  passage  of  air  to  the  lungs,  or  by  supplying  air 
devoid  of  oxygen,  a  condition  ensues,  which  passes  rapidly  from  the  state 
of  dyspnoea  (difficult  breathing)  to  what  is  termed  asphyxia;  and  the 
latter  quickly  ends  in  death. 

The  ways  by  which  this  condition  of  asphyxia  may  be  produced  are 
very  numerous;  as,  for  example,  by  the  prevention  of  the  due  entry  of 
oxygen  into  the  blood,  either  by  direct  obstruction  of  the  trachea  or  other 
part  of  the  respiratory  passages,  or  by  introducing  instead  of  ordinary  air 
a  gas  devoid  of  oxygen,  or,  again,  by  interference  with  the  due  inter- 
change  of  gases  between  the  air  and  the  blood. 

Symptoms  of  Asphyxia. — The  most  evident  symptoms  of  asphyxia 
or  suffocation  are  well  known.    Violent  action  of  the  respiratory  muscles 

'  This  term  has  been,  unfortunately,  often  applied  to  conditions  of  dyspnoea  or 
aspJiyxia;  but  the  modern  application  of  the  term,  as  in  the  text,  is  the  more  convenient. 
Vol.  I.— 14. 


210 


HAND-BOOK  OF  PHYSIOLOGY. 


and,  more  or  less,  of  all  the  muscles  of  the  body;  lividity  of  the  skin  and 
all  other  vascular  parts,  while  the  veins  are  also  distended,  and  the  tissues 
seem  generally  gorged  with  blood;  convulsions,  quickly  followed  by  in- 
sensibility, and  death. 

The  conditions  which  accompany  these  symptoms  are — 

(1)  More  or  less  interference  with  the  passage  of  the  blood  through 
the  pulmonary  blood-vessels. 

(2)  Accumulation  of  blood  in  the  right  side  of  the  heart  and  in  the 
systemic  veins. 

(3)  Circulation  of  impure  (non-aerated)  blood  in  all  parts  of  the  body. 
Cause  of  Death  from  Asphyxia. — The  causes  of  these  conditions 

and  the  manner  in  which  they  act,  so  as  to  be  incompatible  with  life,  may 
be  here  briefly  considered. 

(1)  The  obstruction  to  the  passage  of  blood  through  the  lungs  is  not 
so  great  as  it  was  once  supposed  to  be;  and  such  as  there  is  occurs  chiefly 
in  the  later  stages  of  asphyxia,  when,  by  the  violent  and  convulsive  action 
of  the  expiratory  muscles,  pressure  is  indirectly  made  on  the  lungs,  and 
the  circulation  through  them  is  proportionately  interfered  with. 

(2)  Accumulation  of  blood,  with  consequent  distension  of  the  right 
side  of  the  heart  and  systemic  veins,  is  the  direct  result,  at  least  in  part, 
of  the  obstruction  to  the  pulmonary  circulation  just  referred  to.  Other 
causes,  however,  are  in  operation,  (a)  The  vaso-motor  centres  stimu- 
lated by  blood  deficient  in  oxygen,  causes  contraction  of  all  the  small 
arteries  with  increase  of  arterial  tension,  and  as  an  immediate  conse- 
quence the  filling  of  the  systemic  veins,  (b)  The  increased  arterial  ten- 
sion is  followed  by  inhibition  of  the  action  of  the  heart,  and,  thus,  the 
latter,  contracting  less  frequently,  and  gradually  enfeebled  also  by  defi- 
cient supply  of  oxygen,  becomes  over-distended  by  blood  which  it  cannot 
expel.  At  this  stage  the  left  as  well  as  the  right  cavities  are  distended 
with  blood. 

The  ill  eifects  of  these  conditions  are  to  be  looked  for  partly  in  the  heart, 
the  muscular  fibres  of  which,  like  those  of  the  urinary  bladder  or  any 
other  hollow  muscular  organ,  may  be  paralyzed  by  over-stretching;  and 
partly  in  the  venous  congestion,  and  consequent  interference  with  the 
function  of  the  higher  nerve-centres,  especially  the  medulla  oblongata. 

(3)  The  passage  of  non-aerated  blood  through  the  lungs  and  its  dis- 
tribution over  the  body  are  events  incompatible  with  life,  in  one  of  the 
higher  animals,  for  more  than  a  few  minutes;  tlie  rapidity  with  which 
deatli  ensues  in  asphyxia  being  due,  more  particularly,  to  the  ofl'ect  of 
iion-oxygcnized  blood  on  the  medulla  oblongata,  and,  through  the  coro- 
nary arteries,  on  the  muscular  substance  of  the  heart.  The  excitability 
of  both  n(n-v()us  aiul  muscular  tissue  is  dependent  on  n  constant  and  large 
supply  of  oxygen,  and,  wheu  this  is  interfered  with,  is  rapidly  lost.  The 
(liiiiinuiion  of  oxygen,  it  may  be  here  remnrked,  has  a  move  direct  in- 


RESPIRATION. 


211 


fluence  in  the  production  of  the  usual  symptoms  of  asphyxia  than  the 
increased  amount  of  carbonic  acid.  Indeed,  the  fatal  effect  of  a  gradual 
accumulation  of  the  latter  in  the  blood,  if  a  due  supply  of  oxygen  be 
maintained,  resembles  rather  that  of  a  narcotic  poison. 

In  some  experiments  performed  by  a  committee  appointed  by  the 
Medico-Chirurgical  Society  to  investigate  the  subject  of  Su!<pended  Ani- 
mation, it  was  found  that,  in  the  dog,  during  simple  asphyxia,  i.e.,  by 
simple  privation  of  air,  as  by  plugging  the  trachea,  the  average  duration 
of  the  respiratory  movements  after  the  animal  had  been  deprived  of  air, 
was  4  minutes  5  seconds;  the  extremes  being  3  minutes  30  seconds,  and 
4  minutes  40  seconds.  The  average  duration  of  the  hearths  action,  on  the 
other  hand,  was  7  minutes  11  seconds;  the  extremes  being  6  minutes  40 
seconds,  and  ?  minutes  45  seconds.  It  would  seem,  therefore,  that  on 
an  average,  the  heart's  action  continues  for  3  minutes  15  seconds  after  the 
animal  has  ceased  to  make  respiratory  efforts.  A  very  similar  relation 
was  observed  in  the  rabbit.  Eecovery  never  took  place  after  the  hearths 
action  had  ceased. 

The  results  obtained  by  the  committee  on  the  subject  of  drowning 
were  very  remarkable,  especially  in  this  respect,  that  whereas  an  animal 
may  recover,  after  simple  deprivation  of  air  for  nearly  four  minutes,  yet, 
after  submersion  in  water  for  1|-  minute,  recovery  seems  to  be  impossible. 
This  remarkable  difference  was  found  to  be  due,  not  to  the  mere  submer- 
sion, nor  directly  to  the  struggles  of  the  animal,  nor  to  depression  of  tem- 
perature, but  to  the  two  facts,  that  in  drowning,  a  free  passage  is  allowed 
to  air  out  of  the  lungs,  and  a  free  entrance  of  water  into  them.  It  is 
probably  to  the  entrance  of  water  into  the  lungs  that  the  speedy  death  in 
drowning  is  mainly  due.  The  results  oi post-mortem  examination  strongly 
support  this  view.  On  examining  the  lungs  of  animals  deprived  of  air 
by  plugging  the  trachea,  they  were  found  simply  congested;  but  in  the 
animals  drowned,  not  only  was  the  congestion  much  more  intense,  accom- 
panied with  ecchymosed  points  on  the  surface  and  in  the  substance  of 
the  lung,  but  the  air  tubes  were  completely  choked  up  with  a  sanious 
foam,  consisting  of  blood,  water,  and  mucus,  churned  up  with  the  air  in 
the  lungs  by  the  respiratory  efforts  of  the  animal.  The  lung-sUbstance, 
too,  appeared  to  be  saturated  and  sodden  with  water,  which,  stained 
slightly  with  blood,  poured  out  at  any  point  where  a  section  was  made. 
The  lung  thus  sodden  with  water  was  heavy  (though  it  floated),  doughy, 
pitted  on  pressure,  and  was  incapable  of  collapsing.  It  is  not  difficult  to 
understand  how,  by  such  infraction  of  the  tubes,  air  is  debarred  from 
reaching  the  pulmonary  cells;  indeed  the  inability  of  the  lungs  to  collapse 
on  opening  the  chest  is  a  proof  of  the  obstruction  which  the  froth  occu- 
pying the  air-tubes  offers  to  the  transit  of  air. 

We  must  carefully  distinguish  the  asphyxiating  effect  of  an  insuffi- 
cient supply  of  oxygen  from  the  directly  poisonous  action  of  such  a  gas 
as  carbonic  oxide,  which  is  present  to  a  considerable  amount  in  common 
coal-gas.  The  fatal  effects  often  produced  by  this  gas  (as  in  accidents 
from  burning  charcoal  stoves  in  small,  close  rooms),  are  due  to  its  enter- 
ing into  combination  with  the  haemoglobin  of  the  blood -corpuscles 
(p.  95),  and  thus  expelling  the  oxygen. 


CHAPTER  VII. 


FOOD. 

In  order  that  life  may  be  maintained  it  is  necessary  that  the  body 
should  be  supplied  with  food  in  proper  quality  and  quantity. 

The  food  taken  in  by  the  animal  body  is  used  for  the  purpose  of  re- 
placing the  waste  of  the  tissues.  And  to  arrive  at  a  reasonable  estimation 
of  the  proper  diet  in  twenty-four  hours  it  is  necessary  to  consider  the 
amount  of  the  excreta  daily  eliminated  from  the  body.  The  excreta  con- 
tain chiefly  carbon,  hydrogen,  oxygen,  and  nitrogen,  but  also  to  a  less 
extent,  sulphur,  phosphorus,  chlorine,  potassium,  sodium,  and  certain 
other  of  the  elements.  Since  this  is  the  case  it  must  be  evident  that,  to 
balance  this  waste,  foods  must  be  supplied  containing  all  these  elements 
to  a  certain  degree,  and  some  of  them,  viz. ,  those  which  take  the  prin- 
cipal "part  in  forming  the  excreta,  in  large  amount.  We  have  seen  in  the 
last  Chapter  that  carlDonic  acid  and  ammonia,  i.e.,  the  elements  carbon, 
oxygen,  nitrogen,  hydrogen,  are  given  off  from  the  lungs.  By  the  excre- 
tion of  the  kidneys — the  urine — many  elements  are  discharged  from  the 
blood,  especially  nitrogen,  hydrogen,  and  oxygen.  In  the  sweat,  the  ele- 
ments chiefly  represented  are  carbon,  hydrogen,  and  oxygen,  and  also  in 
the  faeces.  By  all  the  excretions  large  quantities  of  water  are  got  rid  of 
daily,  but  chiefly  by  the  urine. 

The  relations  between  the  amounts  of  the  chief  elements  contained 
in  these  various  excreta  in  twenty-four  hours  may  be  represented  in  tlie 
following  way  (Landois) : 


By  the  hmgs 
By  the  skin 
By  the  urine 
By  tlie  faeces 

Grammes 


Water. 

C. 

H. 

0. 

330 

248-8 

? 

651.15 

CGO 

2.6 

7-2 

1700 

9-8 

3-3 

15-8 

11-1 

128 

20- 

3- 

3- 

12 

2818 

281-2 

6-3 

18-8 

081-41 

To  this  sliould  be  added  206*  grammes  water,  whicli  jire  produced  by 
the  union  of  liydrogcn  and  oxygen  in  the  body  during  the  process  of  oxi- 
dation (i.e.,  32-80  hydrogen  and  263.41  oxygen).  There  are  twenty-six 
grammes  of  salts  got,  rid  of  l)y  the  urine  and  six  by  the  faeces.    As  the 


FOOD. 


213 


water  can  be  supplied  as  such,  the  losses  of  carbon,  nitrogen,  and  oxygen 
are  those  to  which  we  should  direct  our  attention  in  supplying  food. 

For  the  sake  of  example,  we  may  now  take  only  two  elements,  carbon 
and  nitrogen,  and,  if  we  discover  what  amount  of  these  is  respectively  dis- 
charged in  a  given  time  from  the  body,  we  shall  be  in  a  position  to  judge 
what  kind  of  food  will  most  readily  and  economically  replace  their  loss. 

The  quantity  of  carbon  daily  lost  from  the  body  amounts  to  about 
281*2  grammes  or  nearly  4,500  grains,  and  of  nitrogen  18*8  grammes  or 
nearly  300  grains;  and  if  a  man  could  be  fed  by  these  elements,  as  such, 
the  problem  would  be  a  very  simple  one;  a  corresponding  weight  of 
charcoal,  and,  allowing  for  the  oxygen  in  it,  of  atmospheric  air,  would  be 
all  that  is  necessary.  But  an  animal  can  live  only  upon  these  elements 
when  they  are  arranged  in  a  particular  manner  with  others,  in  the  form 
of  an  organic  compound,  as  albumen,  starch,  and  the  like;  and  the  rela- 
tive proportion  of  carbon  to  nitrogen  in  either  of  these  compounds  alone, 
is,  by  no  means,  the  proportion  required  in  the  diet  of  man.  Thus,  in 
albumen,  the  proportion  of  carbon  to  nitrogen  is  only  as  3*5  to  1.  If, 
therefore,  a  man  took  into  his  body,  as  food,  sufficient  albumen  to  supply 
him  with  the  needful  amount  of  carbon,  he  would  receive  more  than  four 
times  as  much  nitrogen  as  he  wanted;  and  if  he  took  only  sufficient  to 
supply  him  with  nitrogen,  he  would  be  starved  for  want  of  carbon.  It  is 
plain,  therefore,  that  he  should  take  with  the  albuminous  part  of  his 
food,  which  contains  so  large  a  relative  amount  of  nitrogen  in  proportion 
to  the  carbon  he  needs,  substances  in  which  the  nitrogen  exists  in  much 
smaller  quantities  relatively  to  the  carbon. 

It  is  therefore  evident  that  the  diet  must  consist  of  several  substances, 
not  of  one  alone,  and  we  must  therefore  turn  to  the  available  food-stuffs. 
For  the  sake  of  convenience  they  may  be  classified  as  follows: 

A.  Oegan'ic. 

I.  Nitrogenous,  consisting  of  Proteids,  e.g.  albumen,  casein,  syn- 

tonin,  gluten,  legumin  and  their  allies;  and  Gelatins,  which  in- 
clude gelatin,  elastin,  and  chondrin.  All  of  these  contain  car- 
bon, hydrogen,  oxygen,  and  nitrogen,  and  some  in  addition, 
phosphorus  and  sulphur. 

II.  Non-Nitrogenous,  comprising: 

(1.)  Amyloid  or  saccharine  bodies,  chemically  known  as  carbo- 
hydrates, since  they  contain  carbon,  hydrogen,  and  oxygen,  with 
the  last  two  elements  in  the  proportion  to  form  water,  i.e., 
H^O.   To  this  class  belong  starch  and  sugar. 

(2.)  Oils  and  fats. — These  contain  carbon,  hydrogen,  and  oxy- 
gen; but  the  oxygen  is  less  in  amount  than  in  the  amyloids  and 
saccharine  bodies. 

B.  Ikorgakic. 

I.  Mineral  and  saline  matter. 

II.  Water. 


214 


HAND-BOOK  OF  PHYSIOLOGY. 


To  supply  the  loss  of  nitrogen  and  carbon,  it  is  found  by  experience 
that  it  is  necessary  to  combine  substances  which  contain  a  large  amount 
of  nitrogen  with  others  in  which  carbon  is  in  considerable  amount;  and 
although,  without  doubt,  if  it  were  possible  to  relish  and  digest  one  or 
other  of  the  above-mentioned  proteids  when  combined  with  a  due  quantity 
of  an  amyloid  to  supply  the  carbon,  such  a  diet,  together  with  salt  and 
water,  ought  to  support  life;  yet  we  find  that  for  the  purposes  of  ordinary 
life  this  system  does  not  answer,  and  instead  of  confining  our  nitrogenous 
foods  to  one  variety  of  substance  we  obtain  it  in  a  large  number  of  allied 
substances,  for  example,  in  flesh,  of  bird,  beast,  or  fish;  in  eggs;  in  milk; 
and  in  vegetables.  And,  again,  we  are  not  content  with  one  kind  of  ma- 
terial to  supply  the  carbon  necessary  for  maintaining  life,  but  seek  more, 
in  bread,  in  fats,  in  vegetables,  in  fruits.  Again,  the  fluid  diet  is  seldom 
supplied  in  the  form  of  pure  water,  but  in  beer,  in  wines,  in  tea  and  cof- 
fee, as  well  as  in  fruits  and  succulent  vegetables. 

Man  requires  that  his  food  should  be  cookecL  Very  few  organic  sub- 
stances can  be  properly  digested  without  previous  exposure  to  heat  and 
to  other  manipulations  which  constitute  the  process  of  cooking.  It  will 
be  well,  therefore,  to  consider  the  composition  of  the  various  substances 
employed  as  food,  and  then  to  consider  how  they  are  affected  by  cooking. 

iA.  Foods  coKTAii^-iifG  principally  Nitrogenous  bodies. 

I. — Flesh  of  Animals,  especially  of  the  ox  (beef,  veal),  sheep  (mutton, 
lamb),  pig  (pork,  bacon,  ham). 

Of  these,  beef  is  richest  in  nitrogenous  matters,  containing  about  20 
per  cent.,  whereas  mutton  contains  about  18  per  cent.,  veal,  16-5,  and 
pork,  10;  the  flesh  is  also  firmer,  more  satisfying,  and  is  supposed  to  be 
more  strengthening  than  mutton,  whereas  the  latter  is  more  digestible. 
The  flesh  of  young  animals,  such  as  lamb  and  -veal,  is  less  digestible  and 
less  nutritious.  Pork  is  comparatively  indigestible,  and  contains  a  large 
amount  of  fat. 

Flesh  contains: — (1)  Nitrogenous  bodies:  myosin,  serum-albumin,  gela- 
tin (from  the  interstitial  flbrous  connective  tissue);  eiastin  (from  the  elastic 
tissue),  as  well  as  IminogloUn.  (2)  Fatty  matters,  including  lecithin  and 
cholesterin.  (3)  Extractive  matters,  some  of  which  are  agreeable  to  the 
palate,  e.g.,  osmazome,  and  others  which  are  weakly  stimulating,  e.g., 
kreatin.  Besides,  there  are  sarcolactic  and  inositic acids,  taurin,  xantliin, 
and  others.  (4)  Salts,  cliiefly  of  potassium,  calcium,  and  magnesium. 
(5)  Water,  the  amount  of  wliicli  varies  from  15  per  cent,  in  dried  bacon 
to  39  in  pork,  51  to  53  in  fat  beef  and  mutton,  to  72  })cr  cent,  in  lean 
beef  and  mutton.  (G)  A  certain  amount  of  carbo-hydrate  material  is 
found  in  the  flesli  of  young  animals,  in  the  form  of  inosite,  dextrin,  grape 
sugar,  and  (in  young  animals)  glycogen. 


FOOD. 


215 


Table  of  Per-centage  Comjjosition  of  Beef  Mutton,  Pork,  and  Veal. — 

{Lethehy. ) 


Water. 

Albumen. 

Fat. 

Salts 

Beef. — Lean  . 

.  72 

19-3 

3-6 

5.1 

Fat  . 

.  51 

14-8 

29-8 

4-4 

Mutton. — Lean 

.  72 

18.3 

4.9 

4.8 

Fat 

.  53 

12-4 

31-1 

3-5 

Veal  . 

.  63 

16-5 

15-8 

4-7 

Pork.— Fat  . 

.  39 

9.8 

48-9 

2-3 

Together  with  the  flesh  of  the  above-mentioned  animals^  that  of  the 
deer,  hare,  rabUt,  and  birds,  constituting  venison,  game  and  poultry, 
should  be  added  as  taking  part  in  the  supply  of  nitrogenous  substances, 
and  edsofish — salmon,  eels,  etc.,  and  shell- fish,  e.g.,  lobster,  crab,  mussels, 
oysters,  shrimps,  scollop,  cockles,  etc. 


Table  of  Per-centage  Composition  of  Poultry  and  Fish. — (Letheby.) 

Water.  Albumen.     Fats.  Salts. 
Poultry   74        21         3*8  1-2 

(Singularly  devoid  of  fat,  and  so  generally  eaten  with  bacon  or  pork.) 

White  Fish   .       .  .  .78  18-1  2-9  1- 

Salmon         .       .  .  .77  16.1  5-5  1*4 

Eels  (very  rich  in  fat)  .  .75  9-9  13-8  1-3 

Oysters        .       .  .  .75-74  11-72  2-42  2.73 

Even  now  the  list  of  fleshy  foods  is  not  complete,  as  nearly  all  animals 
have  been  occasionally  eaten,  and  we  may  presume  that  the  average  com- 
position of  all  is  nearly  the  same. 

II.  MilJc — Is  intended  as  the  *  entire  food  of  young  animals,  and  as 
such  contains,  when  pure,  all  the  elements  of  a  typical  diet.  (1)  Albu- 
minous substances  in  the  form  of  casein  and,  in  small  amount,  of  serum- 
albumin.  (2)  Fats  in  the  cream.  (3)  Carbo-hydrates  in  the  form  of 
lactose  or  milk  sugar.  (4)  Salts,  chiefly  calcium  phosphate;  and  (5) 
Water.  From  it  we  obtain  (a)  cheese,  which  is  the  casein  precipitated 
with  more  or  less  fat  according  as  the  cheese  is  made  of  skim  milk  (skim 
cheese),  of  fresh  milk  with  its  cream  (Cheddar  and  Cheshire),  or  of  fresh 
milk  plus  cream  (Stilton  and  double  Gloucester).  The  precipitated  casein 
is  allowed  to  ripen,  by  which  process  some  of  the  albumen  is  split  up  with 
formation  of  fat.  (/?)  Cream,  which  consists  of  the  fatty  globules  in- 
cased in  casein,  and  which  being  of  low  specific  gravity  float  to  the  surface. 
{y)  Butter,  or  the  fatty  matter  deprived  of  its  casein  envelope  by  the  process 
of  churning.     (6)  Buttermilk,  or  the  fluid  obtained  from  cream  after 


216 


HAND-BOOK  OF  PHYSIOLOGY. 


batter  has  been  formed;  very  rich  therefore  in  nitrogen,  (f)  WJiey,  or 
the  fluid  which  remains  after  the  precipitation  of  casein;  this  contains 
sugar,  salt,  and  a  small  quantity  of  albumen.  ' 

Table  of  Composition  of  Milk,  Buttermilk,  Cream,  and  Cheese. — {LetJie- 

dy  and  Pay  en.) 


Nitrogenous  -p 
matters. 


Lactose.    Salts.  Water. 


Milk  (Cow) 
Buttermilk 
Cream 

Cheese.  — Skim  . 

Cheddar 


4-1 
4-1 
2-7 
44-8 
28-4 


3-9 
•7 
26-7 

6-3 
31-1 


5.2 
6-4 
2-8 


1-8 
4-9 
4.5 


86 
88 
66 
44 
36 


Non- nitrogenous 
matter  and  loss. 


"   ISTeufchatel  (fresh)  8-       40-71     36-58       -51  36.58 

III.  Eggs. — The  yelk  and  albumen  of  eggs  are  in  the  same  relation  as 
food  for  the  embryoes  of  oviparous  animals  that  milk  is  to  the  young  of 
mammalia,  and  afford  another  example  of  the  natural  admixture  of  the 
various  alimentary  principles. 


Tahle  of  the  Per-centage  Composition  of  Foiuls'  Eggs. 

Salts.  Water. 


White 
Yelk 


Nitrogenous 
substances. 

.  20-4 
.  16 


Fats. 


30-7 


1-6 
1-3 


78 
52 


IV.  Leguminous  fruits  are  used  by  vegetarians,  as  the  chief  soui'ce  of 
the  nitrogen  of  the  food.  Those  chiefly  used  eivepeas,  beans,  lentils,  etc., 
they  contain  a  nitrogenous  substance  called  legumin,  allied  to  albumen. 
They  contain  about  25  -30  per  cent,  of  this  nitrogenous  body,  and  twice  as 
much  nitrogen  as  wheat. 


B.     SUBSTAH-CES  SUPPLYING  PRINCIPALLY  CARBOHYDRATE  BODIES. 

a.  Bread,  made  from  the  ground  grain  obtained  from  various  so-called 
cereals,  viz.,  wheat,  rye,  maize,  barley,  rice,  oats,  etc.,  is  the  direct  form 
in  which  the  carbohydrate  is  supplied  in  an  ordinary  diet.  Flour,  how- 
ever, besides  the  starch,  contains  gluten,  a  nitrogenous  body,  and  »  small 
amount  of  fat. 

Table  of  Par-MnUige  Composition  of  Bread  nnd  Fhnr. 

.Kit"ogcnou8    Carbo-     p  ^  ^  ^ 

matters,  iiydrates 

Bread  .  .  .8-1  51-  1 -G  2.3  37 
Flour  .       .10.8        70-85     2-        1.7  15 


FOOD. 


217 


Various  articles  of  course  are  made  from  flour,  e.g.,  macaroni,  biscuits, 
etc.,  besides  bread. 

/?.  Vegetables,  especially  potatoes. 

y.  Fruits  contain  sugar,  and  organic  acids,  tartaric,  malic,  citric,  and 
others. 

C.  Substances  supplying  pkincipally  Fatty  bodies. 
The  chief  are  butter ,  lard  (pig's  fat),  suet  (beef  and  mutton  fat). 

D.  Substances  supplying  the  Salts  of  the  food. 

Nearly  all  the  foregoing  substances  in  A,  B,  and  C,  contain  a  greater  or 
less  amount  of  the  salts  required  in  food;  but  green  vegetables  and  fruit 
supply  certain  salts,  without  which  the  normal  health  of  the  body  is  not 
maintained. 

B.  Liquid  Foods. 

Water  is  consumed  alone,  or  together  with  certain  other  substances 
used  to  flavor  it,  e.g.,  tea,  coffee,  etc.  Tea  in  moderation  is  a  stimulant, 
and  contains  an  aromatic  oil  to  which  it  owes  its  peculiar  aroma,  an  astrin- 
gent of  the  nature  of  tannin,  and  an  alkaloid,  theine.  The  composition 
of  coflee  is  very  nearly  similar  to  that  of  tea.  Cocoa,  in  addition  to 
similar  substances  contained  in  tea  and  coffee,  contains  fat,  albuminous 
matter,  and  starch,  and  must  be  looked  upon  more  as  a  food. 

Beer,  in  various  forms,  is  an  infusion  of  malt  (barley  which  has 
sprouted,  and  in  which  the  starch  is  converted  in  great  part  into  sugar), 
boiled  with  hops  and  allowed  to  ferment.  Beer  contains  from  1  '2  to  8  '8 
per  cent,  of  alcohol. 

Cider  and  Perry,  the  fermented  juice  of  the  apple  and  pear. 

Wine,  the  fermented  juice  of  the  grape,  contains  from  6  or  7  (Ehine 
wines,  and  white  and  red  Bordeaux)  to  24 — 25  (ports  and  sherries)  per 
cent,  of  alcohol. 

Spirits,  obtained  from  the  distillation  of  fermented  liquors.  They 
contain  upward  of  40 — 70  per  cent,  of  absolute  alcohol. 

Effects  cf  cooking  upon  Food. — In  general  terms  this  may  be 
said  to  make  food  more  easily  digestible,  and  this  includes  two  other 
alterations,  food  is  made  more  agreeable  to  the  palate  and  also  more  pleas- 
ing to  the  eye.  Cooking  consists  in  exposing  the  food  to  various  degrees 
of  heat,  either  to  the  direct  heat  of  the  fire,  as  in  roasting,  or  to  the  in- 
direct heat  of  the  fire,  as  in  broiling,  baking,  or  frying,  or  to  hot  water, 
as  in  boiling  or  stewing.  The  effect  of  heat  upon  flesh  is  to  coagulate  the 
albumen  and  coloring  matter,  to  solidify  fibrin,  and  to  gelatinize  tendons 


218 


HAND-BOOK  OF  PHYSIOLOGY. 


and  fibrous  connective  tissue.  Previous  beating  or  bruising  (as  with 
steaks  and  chops,  or  keeping  (as  in  the  case  of  game),  renders  the  meat 
more  tender.  Prolonged  exposure  to  heat  also  develops  on  the  surface 
certain  empyreumatic  bodies,  which  are  agreeable  both  to  the  taste  and 
smell.  By  placing  meat  into  hot  water,  the  external  coating  of  albumen 
is  coagulated,  and  very  little,  if  any,  of  the  constituents  of  the  meat  are 
lost  afterward  if  boiling  be  prolonged,  but  if  the  constituents  of  the 
meat  are  to  be  extracted,  it  should  be  exposed  to  prolonged  simmering  at 
a  much  lower  temperature,  and  the  '^Iroth"  will  then  contain  the  gelatin 
and  extractive  matters  of  the  meat,  as  well  as  a  certain  amount  of  albu- 
men.   The  addition  of  salt  will  help  to  extract  the  myosin. 

The  effect  of  boiling  upon  an  egg  coagulates  the  albumen,  and  helps 
in  rendering  the  article  of  food  more  suitable  for  adult  dietary.  Upon 
milk,  the  effect  of  heat  is  to  produce  a  scum  composed  of  serum-albumin 
and  a  little  casein  (the  greater  part  of  the  casein  being  uncoagulated)  with 
some  fat.  Upon  vegetables,  the  cooking  produces  the  necessary  effect  of 
rendering  them  softer,  so  that  they  can  be  more  readily  broken  up  in  the 
mouth;  it  also  causes  the  starch  to  swell  up  and  burst,  and  so  aids  the 
digestive  fluids  to  penetrate  into  their  substance.  The  albuminous  mat- 
ters are  coagulated,  and  the  gummy,  saccharine  and  saline  matters  are 
removed.  The  conversion  of  flour  into  bread  is  effected  by  mixing  it  with 
water,  a  little  salt  and  a  certain  amount  of  yeast,  which  consists  of  the 
cells  of  an  organized  ferment  {Torula  cerevisice).  By  the  growth  of  this 
plant,  which  lives  upon  the  sugar -produced  from  the  starch  of  the  flour, 
carbonic  acid  gas  and  a  small  amount  of  alcohol  are  formed.  It  is  by 
means  of  the  former  that  the  dough  rises.  Another  method  consists  in 
mixing  the  flour  with  water  containing  a  large  quantity  of  tlie  gas  in  so- 
lution. 

By  the  action  of  heat  during  baking  the  dough  continues  to  expand, 
and  the  gluten  being  coagulated,  the  bread  sets  as  a  permanently  vesicu- 
lated  mass. 

I. — Effects  of  an  insufficient  Diet. 

Hunger  and  Thirst. — The  sensation  of  liunger  is  manifested  in 
consequence  of  deficiency  of  food  in  the  system.  The  mind  refers  the 
sensation  to  the  stomach;  yet  since  the  sensation  is  relieved  by  the  intro- 
duction of  food  either  into  the  stomach  itself,  or  into  the  blood  through 
other  channels  than  the  stomach,  it  would  appear  not  to  depend  on  the 
state  of  the  stomach  alone.  Tliis  view  is  confirmed  by  the  fact,  that  tlie 
division  of  ])ot]i  pncumogastric  nerves,  wliich  are  the  principal  channels 
])y  \vlii(;li  th(^  brain  is  cognizant  of  the  condition  of  the  stomach,  does  not 
a})i)ear  to  alhiy  the  seiisiitions  of  hunger.  But  that  the  stomach  has 
some  share  in  tliis  sensation  is  proved  by  tlie  relief  afforded,  though  only 


FOOD. 


temporarily,  by  the  introduction  of  even  non-alimentary  substances  into 
this  organ.  It  may,  therefore,  be  said  that  the  sensation  of  hunger  is 
caused  both  by  a  want  in  the  system  generally,  and  also  by  the  condition 
of  the  stomach  itself,  by  which  condition,  of  course,  its  own  nerves  are 
more  directly  affected. 

The  sensation  of  thirst,  indicating  the  want  of  fluid,  is  referred  to  the 
fauces,  although,  as  in  hunger,  this  is,  in  great  part,  only  the  local  decla- 
ration of  a  general  condition.  For  thirst  is  relieved  for  only  a  very  short 
time  by  moistening  the  dry  fauces;  but  maybe  relieved  completely  by  the 
introduction  of  liquids  into  the  blood,  either  through  the  stomach,  or  by 
injections  into  the  blood-vessels,  or  by  absorption  from  the  surface  of  the 
skin  or  the  intestines.  The  sensation  of  thirst  is  perceived  most  naturally 
whenever  there  is  a  disproportionately  small  quantity  of  water  in  the 
blood:  as  well,  therefore,  when  water  has  been  abstracted  from  the  blood, 
as  when  saline  or  any  solid  matters  have  been  abundantly  added  to  it. 
And  the  cases  of  hunger  and  thirst  are  not  the  only  ones  in  which  the 
mind  derives,  from  certain  organs,  a  peculiar  predominant  sensation  of 
some  condition  affecting  the  whole  body.  Thus,  the  sensation  of  the 
"necessity  of  breathing,^'  is  referred  especially  to  the  air-passages;  but, 
as  Volkmann^s  experiments  show,  it  depends  on  the  condition  of  the 
blood  which  circulates  everywhere,  and  is  felt  even  after  the  lungs  of 
animals  are  removed;  for  they  continue,  even  then,  to  gasp  and  manifest 
the  sensation  of  want  of  breath. 

Starvation. — The  effects  of  total  deprivation  of  food  have  been  made 
the  subject  of  experiments  on  the  lower  animals,  and  have  been  but  too 
frequently  illustrated  in  man.  (1)  One  of  the  most  notable  effects  of 
starvation,  as  might  be  expected,  is  loss  of  weight;  the  loss  being  greatest 
at  first,  as  a  rule,  but  afterward  not  varying  very  much,  day  by  day,  until 
death  ensues.  Chossat  found  that  the  ultimate  proportional  loss  was,  in 
different  animals  experimented  on,  almost  exactly  the  same;  death 
occurring  when  the  body  had  lost  two-fifths  (forty  per  cent. )  of  its  original 
weight.  Different  parts  of  the  body  lose  weight  in  very  different  propor- 
tions. The  following  results  are  taken,  in  round  numbers,  from  the  table 
given  by  M.  Chossat:— 


Fat      .       .  . 

Blood  . 
Spleen  . 
Pancreas 
Liver  . 
Heart  . 
Intestines 

Muscles  of  locomotion 
Stomach 

Pharynx,  ((Esophagus) 
Skin 


loses  93  per  cent. 
75 
71 
04 
52 

44  " 
42 
42 

39  " 
34 
33 


220 


HAND-BOOK  OF  PHYSIOLOGY. 


Kidneys  loses  31  per  cent. 

Eespiratory  apparatus  22  " 

Bones  ,  16 

Eyes  10 

Nervous  s3-stem  2     "  (nearly). 

(2.)  The  effect  of  starvation  on  the  temperature  of  the  various  animals 
experimented  on  by  Chossat  was  very  marked.  For  some  time  the  mn- 
atiou  in  the  daily  temperature  was  more  marked  than  its  absolute  and 
continuous  diminution,  the  daily  fluctuation  amounting  to  5°  or  6°  F. 
(3°  C),  instead  of  1°  or  2°  F.  (-5^  to  1^  C),  as  in  health.  But  a  short 
time  before  death,  the  temperature  fell  very  rapidly,  and  death  ensued 
when  the  loss  had  amounted  to  about  30^  F.  (16 -5 "^C).  It  has  been  often 
said,  and  with  truth,  although  the  statement  requires  some  qualification, 
that  death  by  starvation  is  really  death  by  cold;  for  not  only  has  it  been 
found  that  differences  of  time  with  regard  to  the  period  of  the  fatal  result 
are  attended  by  the  same  ultimate  loss  of  heat,  but  the  effect  of  the  appli- 
cation of  external  warmth  to  animals  cold  and  dying  from  starvation,  is 
more  effectual  in  reviving  them  than  the  administration  of  food.  In 
other  words,  an  animal  exhausted  by  deprivation  of  nourishment  is  unable 
so  to  digest  food  as  to  use  it  as  fuel,  and  therefore  is  dependent  for  heat 
on  its  supply  from  without.  Similar  facts  are  often  observed  in  the  treat- 
ment of  exhaustive  diseases  in  man. 

(3.)  The  symptoms  produced  by  starvation  in  the  human  subject  are 
hunger,  accompanied,  or  it  may  be  replaced  by  pain,  referred  to  the  region 
of  the  stomach;  insatiable  thirst;  sleeplessness;  general  weakness  and 
emaciation.  The  exhalations  both  from  the  lungs  and  skin  are  fetid, 
indicating  the  tendency  to  decomposition  which  belongs  to  badly- 
nourished  tissues;  and  death  occurs,  sometimes  after  the  additional  ex- 
haustion caused  by  diarrhoea,  often  with  symptoms  of  nervous  disorder, 
delirium  or  convulsions. 

(4.)  In  the  human  subject  death  commonly  occurs  within  six  to  ten 
days  after  total  deprivation  of  food.  But  this  period  may  be  considerably 
prolonged  by  taking  a  very  small  quantity  of  food,  or  even  water  only. 
The  cases  so  frequently  related  of  survival  after  many  days,  or  even  some 
weeks,  of  abstinence,  have  been  due  either  to  the  last-mentioned  circum- 
stances, or  to  others  no  less  effectual,  which  prevented  the  loss  of  heat 
and  moisture.  Cases  in  which  life  has  continued  after  total  abstinence 
from  food  and  drink  for  many  weeks,  or  months,  exist  only  in  the  imag- 
ination of  the  vulgar. 

(5.)  The  appearances  presented  after  death  from  starvation  are  tliose  of 
general  wasting  and  bloodlcssness,  the  latter  condition  being  least  noticeable 
in  the  brain.  The  stomach  and  intestines  are  empty  and  contracted,  and 
tlic  walls  of  the  latter  appear  remarkably  thinned  and  almost  transparent 
The  various  secretions  are  scanty  or  absent,  witli  the  exception  of  the 


FOOD. 


221 


bile,  which,  somewhat  concentrated,  usually  fills  the  gall-bladder.  All 
parts  of  the  body  readily  decompose. 

II. — Effects  of  improper  Diet. 

Experiments  on  Feeding. — Experiments  illustrating  the  ill  effects 
produced  by  feeding  animals  upon  one  or  two  alimentary  substances  only 
liave  been  often  performed. 

Dogs  were  fed  exclusively  on  sugar  and  distilled  water.  During  the 
first  seven  or  eight  days  they  were  brisk  and  active,  and  took  their  food 
and  drink  as  usual;  but  in  the  course  of  the  second  week,  they  began  to 
get  thin,  although  their  appetite  continued  g^ood,  and  they  took  daily 
between  six  and  eight  ounces  of  sugar.  The  emaciation  increased  during 
the  third  week,  and  they  became  feeble,  and  lost  their  activity  and  appe- 
tite. At  the  same  time  an  ulcer  formed  on  each  cornea,  followed  by  an 
escape  of  the  humors  of  the  eye:  this  took  place  in  repeated  experiments. 
The  animals  still  continued  to  eat  three  or  four  ounces  of  sugar  daily; 
but  became  at  length  so  feeble  as  to  be  incapable  of  motion,  and  died  on 
a  day  varying  from  the  thirty-first  to  the  thirty-fourth.  On  dissection, 
their  bodies  presented  all  the  appearances  produced  by  death  from  starva- 
tion; indeed,  dogs  will  live  almost  the  same  length  of  time  without  any 
food  at  all. 

When  dogs  were  fed  exclusively  on  gum,  results  almost  similar  to  the 
above  ensued.  When  they  were  kept  on  olive-oil  and  ivater,  all  the  phe- 
nomena produced  were  the  same,  except  that  no  ulceration  of  the  cornea 
took  place;  the  effects  were  also  the  same  with  butter.  The  experiments  of 
Chossat  and  Letellier  prove  the  same;  and  in  men,  the  same  is  shown  by 
the  various  diseases  to  which  those  who  consume  but  little  nitrogenous 
food  are  liable,  and  especially  by  the  affection  of  the  cornea  which  is 
observed  in  Hindus  feeding  almost  exclusively  on  rice.  But  it  is  not  only 
the  non-nitrogenous  substances,  which,  taken  alone,  are  insufficient  for 
the  maintenance  of  health.  The  experiments  of  the  Academies  of  France 
and  Amsterdam  were  equally  conclusive  that  gelatin  alone  soon  ceases  to 
be  nutritive. 

Savory's  observations  on  food  confirm  and  extend  the  results  obtained 
by  Magendie,  Chossat,  and  others.  They  show  that  animals  fed  exclu- 
sively on  non-nitrogenous  diet  speedily  emaciate  and  die,  as  if  from  starv- 
ation; that  life  is  much  more  prolonged  in  those  fed  with  nitrogenous 
than  by  those  with  non-nitrogenous  food;  and  that  animal  heat  is  main- 
tained as  well  by  the  former  as  by  the  latter — a  fact  which  proves,  if 
proof  were  wanting — that  nitrogenous  elements  of  food,  as  well  as  non- 
nitrogenous,  may  be  regarded  as  calorifacient. 


222 


HAND-BOOK  OF  PHYSIOLOGY. 


III. — Effect  of  too  much  Food. 

Sometimes  the  excess  of  food  is  so  great  that  it  passes  through  the  ali- 
mentary canal,  and  is  at  once  got  rid  of  by  increased  peristaltic  action  of 
the  intestines.  In  other  cases,  the  nnabsorbed  portions  undergo  putre- 
factive changes  in  the  intestines,  which  are  accompanied  by  the  produc- 
tion of  gases,  such  as  carbonic  acid,  carburetted  and  sulphuretted  hydro- 
gen; a  distended  condition  of  the  bowels,  accompanied  by  symptoms  of 
indigestion,  is  the  result.  An  excess  of  the  substances  required  as  food  may, 
however,  undergo  absorption.  It  is  a  well-known  fact  that  numbers  of 
people  habitually  eat  too  much;  especially  of  nitrogenous  food.  Dogs 
can  digest  an  immense  amount  of  meat  if  fed  often,  and  the  amount  of 
meat  taken  by  some  men  would  supply  not  only  the  nitrogen,  but  the 
carbon  which  is  requisite  for  an  ordinary  natural  diet.  A  method  of  get- 
ting rid  of  an  excess  of  nitrogen  is  provided  by  the  digestive  processes  in 
the  duodenum,  to  be  presently  described,  whereby  the  excess  of  the  albu- 
minous food  is  capable  of  being  changed  before  absorption  into  nitroge- 
nous crystalline  matters,  easily  converted  by  the  liver  into  urea,  and  so  easily 
excreted  by  the  kidneys,  affording  one  variety  of  what  is  called  hixiis 
consumption;  but  after  a  time  the  organs,  especially  the  liver,  will  yield 
to  the  strain  of  the  over- work,  and  will  not  reduce  the  excess  of  nitroge- 
nous material  into  urea,  but  into  other  less  oxidized  products,  such  as  uric 
acid;  and  general  plethora  and  gout  may  be  the  result.  This  state  of 
things,  however,  is  delayed  for  a  long  time,  if  not  altogether  obviated, 
when  large  meat-eaters  take  a  considerable  amount  of  exercise. 

Excess  of  carbohydrate  food  produces  an  accumulation  of  fat,  which 
may  not  only  be  an  inconvenience  by  causing  obesity,  but  may  interfere 
with  the  proper  nutrition  of  muscles,  causing  a  feebleness  of  the  action 
of  the  heart,  and  other  troubles.  The  accumulation  of  fat  is  due  to  the 
excess  of  carbohydrate  being  stored  up  by  the  protoplasm  in  the  form  of 
fat.  Starches  when  taken  in  great  excess  are  almost  certain  to  give  rise  in 
addition  to  dyspepsia,  with  acidity  and  flatulence.  There  is  a  limit  to 
the  absorption  of  starch  and  of  fat,  as,  if  taken  beyond  a  certain  amount, 
they  appear  unchanged  in  the  fjeces. 

Requisites  of  a  Normal  Diet. — It  will  have  been  understood  that 
it  is  necessary  that  a  normal  diet  should  be  made  up  of  various  articles, 
that  they  should  be  well  cooked,  and  should  contain  about  the  same 
amount  of  the  carbon  and  nitrogen  that  are  got  rid  of  by  the  excreta. 
Witliout  doubt  these  desiderata  may  be  satisfied  in  numerous  ways,  and 
it  would  be  sini])ly  absurd  to  believe  that  the  diet  of  every  adult  should 
be  exactly  similar.  The  age,  sex,  strength,  and  circumstances  of  each 
individual  should  ultimately  determine  his  diet.  A  dinner  of  bread  and 
liard  cheese  with  an  onion  contain  all  the  requisites  for  a  meal;  but  such 


FOOD. 


223 


diet  would  be  suitable  only  for  those  possessing  strong  digestive  powers. 
It  is  a  well-known  fact  that  the  diet  of  the  continental  nations  differs 
from  that  of  our  own  country,  and  that  of  cold  from  that  of  hot  climates; 
but  the  same  principle  underlies  them  all,  viz.,  rej)lacemeiit  of  the  loss 
of  the  excreta  in  the  most  convenient  and  economical  way  possible. 
Without  going  into  detail  in  the  matter,  it  may  be  said  that  any  one  in 
active  work  requires  more  nitrogenous  matter  than  one  at  rest,  and  that 
children  and  women  require  less  than  adult  men. 

The  quantity  of  food  for  a  healthy  adult  man  of  average  height  and 
weight  may  be  stated  in  the  following  table: — 

TaUe  of  Water  and  Food  required  for  a  Healthy  Adult. — (Parkes,) 


In  laborious 
occupation. 


At  rest. 


Nitrogenous  substances,  e.g.,  flesh     6  to  7  oz.  av.  2*5  oz. 

Fats   3-5  to  4-5  oz.  1  oz. 

Carbo-hydrates    .       .       .       .  16  to  18  oz.  12  oz. 

Salts   ......  1.2  to  1.5  oz.  .5  oz. 


26-7  to  31  oz.       16  oz. 

The  above  is  the  dry  food;  but  as  this  is  nearly  always  combined  with 
60  to  60  per  cent,  of  water,  these  numbers  should  be  doubled,  and  they 
would  then  be  52  to  60  oz.,  and  32  oz.  of  so  called  solid  food,  and  to  this 
should  be  added  50  to  80  oz.  of  fluid. 


Full  diet  scale  for  an  adult  male  in  hospital  (St.  Bartholomew's 

Hospital). 

Breakfast. — 1  pint  of  tea  (with  milk  and  sugar),  bread  and  butter. 
Dinner. — |-lb.  of  cooked  meat,  ^Ib.  potatoes,  bread  and  beer. 
Tea. — 1  pint  of  tea,  bread  and  butter. 
Supper. — Bread  and  butter,  beer. 

Daily  allotoance  to  each  patient. — 2  pints  of  tea,  with  milk  and  sugar; 
14  oz.  bread;  -|  lb.  of  cooked  meat:  |-lb.  potatoes:  2  pints  of  beer,  1  oz. 
butter.    31  oz.  solid,  and  4  pints  (80  oz.),  liquid. 


CHAPTEE  VIII. 


DIGESTION. 

The  object  of  digestion  is  to  prepare  the  food  to  supply  tlie  waste  of 
tlie  tissues,  wliicli  we  have  seen  is  its  proper  function  in  the  economy. 
Few  of  the  articles  of  diet  are  taken  in  the  exact  condition  in  which  it  is 
possible  for  them  to  be  absorbed  into  the  system  by  the  blood-vessels  and 
lymphatics,  without  which  absorption  they  would  be  useless  for  the  pur- 
poses they  have  to  fulfil;  almost  the  whole  of  the  food  undergoes  Tarious 
changes  before  it  is  fit  for  absorption.  Having  been  received  into  the 
mouth,  it  is  subjected  to  the  action  of  the  teeth  and  tongue,  and  is  mixed 
with  the  first  of  the  digestive  juices — the  saliva.  It  is  then  swallowed, 
and,  passing  through  the  pharynx  and  oesophagus  into  the  stomach,  is 
subjected  to  the  action  of  the  gastric  juice.  Thence  it  passes  into  the 
intestines,  where  it  meets  with  the  bile,  the  pancreatic  juice  and  the  in- 
testinal juices,  all  of  which  exercise  an  influence  upon  that  portion  of  the 
food  not  absorbed  from  the  stomach.  By  this  time  most  of  the  food  is 
capable  of  absorption,  and  the  residue  of  undigested  matter  leaves  the 
body  in  the  form  of  faeces  by  the  anus. 

The  course  of  the  food  through  the  alimentary  canal  of  man  will  be 
readily  seen  from  the  accompanying  diagram  (Fig.  165). 

The  Mouth  is  the  cavity  contained  between  the  jaws  and  inclosed 
by  the  cheeks  laterally,  and  by  the  lips  in  front;  behind  it  opens  into  the 
pharynx  by  the  fauces,  and  is  separated  from  the  nasal  cavity  by  the  hard 
palate  in  front,  and  the  soft  palate  behind,  which  form  its  roof.  The 
tongue  forms  the  lower  part  or  floor.  In  the  jaws  are  contained  tlie 
teeth;  and  when  the  mouth  is  shut  these  form  its  anterior  and  lateral 
boundaries.  The  whole  of  the  mouth  is  lined  with  mucous  membrane, 
covered  by  stratified  squamous  epithelium,  which  is  continuous  in  front 
along  the  lips  with  the  epithelium  of  the  skin,  and  posteriorly  with  that 
of  the  pharynx.  The  mucous  membrane  is  provided  with  numerous 
glands  (small  tubular),  called  mucous  glands,  and  into  it  open  the  ducts 
of  the  salivary  glands,  three  chief  glands  on  each  side.  The  tongue  is 
not  only  a  prehensile  organ,  but  is  also  the  chief  seat  of  the  sense  of  taste. 

We  shall  now  consider,  in  detail,  the  process  of  digestion,  as  it  takes 
place  in  each  stage  of  this  journey  of  the  food  through  the  alimentary 
canal. 

Mastication.— The  act  of  chewiug  or  mastication  is  porformcd  by 


DIGESTION. 


225 


the  biting  and  grinding  movement  of  the  lower  range  of  teeth  against  the 
upper.  The  simultaneous  movements  of  the  tongue  and  cheeks  assist  partly 
by  crushing  the  softer  portions  of  the  food  against  the  hard  palate,  gums, 
etc.,  and  thus  supplementing  the  action  of  the  teeth,  and  partly  by  re- 
turning the  morsels  of  food  to  the  action  of  the  teeth,  again  and  again. 


Fig,  165.— Diagram  of  the  Alimentary  Canal.  The  small  intestine  of  man  is  from  about  3  to  4 
times  as  long  as  the  large  intestine. 

as  they  are  squeezed  out  from  between  them,  until  they  have  been  suffi- 
ciently chewed. 

The  simple  up  and  down,  or  Mting  movements  of  the  lower  jaw,  are 
performed  by  the  temporal,  masseter,  and  internal  pterygoid  muscles,  the 
action  of  which  in  closing  the  jaws  alternates  with  that  of  the  digastric 
and  other  muscles  passing  from  the  os  hyoides  to  the  lower  jaw,  whicK 
open  them.  The  grinding  or  side  to  side  movements  of  the  lower  jaw 
are  performed  mainly  by  the  external  pterygoid  muscles,  the  muscle  of 
one  side  acting  alternately  with  the  other.  When  both  external  ptery- 
VoL.  I.— 15. 


226 


HAND-BOOK  OF  PHYSIOLOGY. 


goids  act  together,  the  lower  jaw  is  pulled  directly  forward,  so  that  the 
lower  incisor  teeth  are  brought  in  front  of  the  level  of  the  upper. 

Temporo-maxillary  Fibro-cartilage.— The  function  of  the  inter- 
articular  fibro- cartilage  of  the  temporo-maxillary  joint  in  mastication 
may  be  here  mentioned.  (1)  As  an  elastic  pad,  it  serves  well  to  distrib- 
ute the  pressure  caused  by  the  exceedingly  powerful  action  of  the  masti- 
catory muscles.  (2)  It  also  serves  as  a  joint-surface  or  socket  for  the 
condyle  of  the  lower  jaw,  when  the  latter  has  been  partially  drawn  for- 
ward out  of  the  glenoid  cavity  of  the  temporal  bone  by  the  external  ptery- 
goid muscle,  some  of  the  fibres  of  the  latter  being  attached  to  its  front 
surface,  and  consequently  drawing  it  forward  with  the  condyle  which 
moves  on  it. 

Nerve-mechanism  of  Mastication. — As  in  the  case  of  so  many 
other  actions,  that  of  mastication  is  partly  voluntary  and  partly  reflex 
and  involuntary.  The  consideration  of  such  sensori-motor  actions  will 
come  hereafter  (see  Chapter  on  the  Nervous  System).  It  will  suffice  here 
to  state  that  the  nerves  chiefly  concerned  are  the  sensory  branches  of  the 
fifth  and  the  glosso-pharyngeal,  and  the  motor  branches  of  the  fifth  and 
the  ninth  (hypoglossal)  cerebral  nerves.  The  nerve-centre  through  which 
the  reflex  action  occurs,  and  by  which  the  movements  of  the  various 
muscles  are  harmonized,  is  situate  in  the  medulla  oblongata.  In  so  far 
as  mastication  is  voluntary  or  mentally  perceived,  it  becomes  so  under 
the  influence,  in  addition  to  the  medulla  oblongata,  of  the  cerebral  hemi- 
spheres. 

Insalivation. — The  act  of  mastication  is  much  assisted  by  the  saliva 
which  is  secreted  by  the  salivary  glands  in  largely  increased  amount 
during  the  process,  and  the  intimate  incorporation  of  which  with  the 
food,  as  it  is  being  chewed,  is  termed  insalivation. 

The  Salivaky  Glai^-ds. 

The  salivary  glands  are  the  parotid,  the  snl-maxillary ,  and  the  sub- 
lingual, and  numerous  smaller  bodies  of  similar  structure,  and  with  sep- 
arate ducts,  which  are  scattered  tliickly  beneath  the  mucous  membrane  of 
the  lips,  cheeks,  soft  palate,  and  root  of  the  tongue. 

Structure. — The  salivary  glands  are  usually  described  as  compound 
tubular  glands.  They  are  made  up  of  lobules.  Each  lobule  consists 
of  the  branchings  of  a  subdivision  of  the  main  duct  of  the  gland,  which 
are  generally  more  or  less  convoluted  toward  tlieir  extremities,  and  some- 
times, according  to  some  observers,  sacculated  or  pouched.  Tlie  convo- 
luted or  pouched  portions  form  the  alveoli,  or  proper  secreting  parts  of 
the  gland.  The  alveoli  arc  composed  of  a  basement  membrane  of  flattened 
(u^lls  joined  together  by  processes  to  produce  a  fenestrated  mombraue,  tlie 
spaces  of  whicli  are  occupied  by  a  homogeneous  ground-substance.  "With- 
in, upon  this  membrane,  whicli  forms  tlie  tube,  the  nucleated  salivary 


DIGESTION. 


227 


secreting  cells,  of  cubical  or  columnar  form,  are  arranged  parallel  to  one 
another  surrounding  a  middle  central  canal.  The  granular  appearance 
which  is  frequently  seen  in  the  salivary  cells  is  due  to  the  very  dense  net- 
work of  fibrils  which  they  contain.  When  isolated,  the  cells  not  unfre- 
quently  are  found  to  be  branched.  Connecting  the  alveoli  into  lobules  is 
a  considerable  amount  of  fibrous  connective  tissue,  which  contains  both 
flattened  and  granular  protoplasmic  cells,  lymph  corpuscles,  and  in  some 
cases  fat  cells.  The  lobules  are  connected  to  form  larger  lobules  (lobes), 
in  a  similar  manner.  The  alveoli  pass  into  the  intralobular  ducts  by  a 
narrowed  portion  (intercalary),  lined  with  flattened  epithelium  with  elon- 
gated nuclei.  The  intercalary  ducts  pass  into  the  intralobular  ducts  by 
a  narrowed  neck,  lined  with  cubical  cells  with  small  nuclei.  The  intra- 
lobular duct  is  larger  in  size,  and  is  lined  with  large  columnar  nucleated 


(K"Uilf  -^^^^"^^^^^^^^     submaxillary  gland  of  dog.   ShowlDg  gland-cells,  b,  and  a  duct,  a,  in  section. 

cells,  the  parts  of  which,  toward  the  lumen  of  the  tube,  presents  a  fine 
longitudinal  striation,  due  to  the  arrangement  of  the  cell  network.  It  is 
most  marked  in  the  submaxillary  gland.  The  intralobular  ducts  pass  into 
the  larger  ducts,  and  these  into  the  main  duct  of  the  gland.  As  tbese 
ducts  become  larger  they  acquire  an  outside  coating  of  connective  tissue, 
and  later  on  some  unstriped  muscular  fibres.  The  lining  of  the  larger 
ducts  consists  of  one  or  more  layers  of  columnar  epithelium,  containing 
an  intracellular  network  of  fibres  arranged  longitudinally. 

Varieties. — Certain  differences  in  the  structure  of  salivary  glands 
may  be  observed  according  as  the  glands  secrete  pure  saliva,  or  saliva 
mixed  with  mucus,  or  pure  mucus,  and  therefore  the  glands  have  been 
classified  as:  (1)  True  salivary  glands  (called  most  unfortunately  by  some 
serous  glands),  e.g.,  the  parotid  of  man  and  other  animals,  and  the  sub- 
maxillary of  the  rabbit  and  guinea-pig  (Fig.  167).  In  this  kind  the 
alveolar  lumen  is  small,  and  the  cells  lining  the  tubule  are  short,  granular 
columnar  cells,  with  nuclei  presenting  the  intranuclear  network.  During 
rest  the  cells  become  larger,  highly  granular,  with  obscured  nuclei,  and 
the  lumen  becomes  smaller.    During  activity,  and  after  stimulation  of 


228 


HAND-BOOK  OF  PHYSIOLOGY. 


the  sympathetic,  the  cells  become  smaller  and  their  contents  more  opaque; 
the  granules  first  of  all  disappearing  from  the  outer  part  of  the  cells,  and 
then  being  found  only  at  the  extreme  inner  part  and  contiguous  border  of 
the  cell.  The  nuclei  reappear,  as  does  also  the  lumen.  (2)  In  the  true 
mucus-secreting  glands,  as  the  sublingual  of  man  and  other  animals,  and 


Fig.  167. 


Fig.  168. 


Fig.  167.— From  a  section  through  a  true  salivary  gland,  a,  the  gland  alveoli,  lined  with  albu- 
minous "  salivary  cells;""  6,  intralobular  duct  cut  transversely.   (Klein  and  Noble  Smith.) 

Fig.  168.— From  a  section  through  a  mucous  gland  in  a  quiescent  state.  The  alveoU  are  Mned  with 
transparent  mucous  cells,  and  outside  these  are  the  demilunes  of  Heidenhain.  The  cells  should  have 
been  represented  as  more  or  less  granular.  (Heidenhain.) 


in  the  submaxillary  of  the  dog,  the  tubes  are  larger,  contain  a  larger 
lumen,  and  also  have  larger  cells  lining  them.  The  cells  are  of  two  kinds, 
{a)  mucous  or  central  cells,  which  are  transparent  columnar  cells  with 
nuclei  near  the  basement  membrane.    The  cell  substance  is  made  up  of  a 

fine  network,  which  in  the  resting  state 
contains  a  transparent  substance  called 
mucigen,  during  which  the  cell  does  not 
stain  well  with  logwood  (Fig.  1G8). 
When  the  gland  is  secreting,  mucigen 
is  converted  into  mucin,  and  the  cells 
swell  up,  appear  more  transparent,  and 
stain  deeply  in  logwood  (Fig.  169). 
During  rest,  the  cells  become  smaller 
and  more  granular  from  having  dis- 
charged their  contents,  and  the  nuclei 
appear  more  distinct,  {h)  Semilunes  of 
Ileidenliain  (Fig.  1G8),  which  are  cre- 
scentic  masses  of  granular  parietal  cells  found  here  and  there  between  the 
basement  membrane  and  the  central  cells.  These  cells  are  small,  and 
liave  a  very  dense  reticulum,  the  nuclei  are  spherical,  and  increase  in  size 
during  secretion.  In  the  mucous  gland  there  are  some  largo  tubes,  lined 
with  large  transparent  central  cells,  and  have  besides  a  fcAV  granular 
parietal  cells;  other  small  tubes  arc  lined  with  small  granular  parietal 


Fig.  169.— a  part  of  a  section  through  a 
mucous  gland  after  prolonged  electrical 
stimulation.  The  alveoli  are  lined  with  small 
granular  cells.  (Lavdovski.) 


DIGESTIOlSr. 


229 


cells  alone;  and  a  third  variety  are  lined  equally  with  each  kind  of  cell. 
(3)  In  the  muco-salivary  or  mixed  glands,  as  the  human  submaxillary 
gland,  part  of  the  gland  presents  the  structure  of  the  mucous  gland, 
whilst  the  remainder  has  that  of  the  salivary  glands  proper. 

Nerves  and  blood-vessels. — Nerves  of  large  size  are  found  in  the  sali- 
vary glands,  they  are  contained  in  the  connective  tissue  of  the  alveoli 
principally,  and  in  certain  glands,  especially  in  the  dog,  are  provided  with 
ganglia.  Some  nerves  have  special  endings  in  Pacinian  corpuscles,  some 
supply  the  blood-vessels,  and  others,  according  to  Pfiiiger,  penetrate  the 
basement  membrane  of  the  alveoli  and  enter  the  salivary  cells. 

The  blood-vessels  form  a  dense  capillary  network  around  the  ducts  of 
the  alveoli,  being  carried  in  by  the  fibrous  trabeculae  between  the  alveoli, 
in  which  also  begin  the  lymphatics  by  lacunar  spaces. 

Saliva. — Saliva,  as  it  commonly  flows  from  the  mouth,  is  mixed  with 
the  secretion  of  the  mucoas  glands,  and  often  with  air  bubbles,  which, 
being  retained  by  its  viscidity,  make  it  frothy.  Wlien  obtained  from  the 
parotid  ducts,  and  free  from  mucus,  saliva  is  a  transparent  watery  fluid, 
the  specific  gravity  of  which  varies  from  1004  to  1008,  and  in  which, 
when  examined  with  the  microscope,  are  found  floating  a  number  of  min- 
ute particles,  derived  from  the  secreting  ducts  and  vesicles  of  the  glands. 
In  the  impure  or  mixed  saliva  are  found,  besides  these  particles,  numer- 
ous epithelial  scales  separated  from  the  surface  of  the  mucous  membrane 
of  the  mouth  and  tongue,  and  the  so-called  salivary  corpuscles,  discharged 
probably  from  the  mucous  glands  of  the  mouth  and  the  tonsils,  which, 
when  the  saliva  is  collected  in  a  deep  vessel,  and  left  at  rest,  subside  in 
the  form  of  a  white  opaque  matter,  leaving  the  supernatant  salivary  fluid 
transparent  and  colorless,  or  with  a  pale  bluish-grey  tint.  In  reaction, 
the  saliva,  when  first  secreted,  appears  to  be  always  alkaline.  During  fast- 
ing, the  saliva,  although  secreted  alkaline,  shortly  becomes  neutral;  and 
it  does  so  especially  when  secreted  slowly  and  allowed  to  mix  with  the 
acid  mucus  of  the  mouth,  by  which  its  alkaline  reaction  is  neutralized. 

Chemical  Composition  of  Mixed  Saliva  (Frerichs). 
Water  ........ 

Solids  

Ptyalin  

Fat  

Epithelium  and  Proteids  (including  Serum-. 

bumin.  Globulin,  Mucin,  &c.)  . 
Salts — Potassium  Sulpho-Cyanate 

Sodium  Phosphate  .... 

Calcium  Phosphate  .... 

Magnesium  Phosphate 

Sodium  Chloride  .... 

Potassiam  Chloride  .... 


5-90 

1-41 
0.07 

2.13 
^  2-29 


5-90 


230  HAND-BOOK  OF  PHYSIOLOGY. 

The  presence  of  potassium  sulphocyanate  (or  tliiocyanate)  (0  N  K  S) 
in  saliva,  may  be  shown  by  the  blood-red  coloration  which  the  fluid  gives 
with  a  solution  of  ferric  chloride  (Fe^OlJ,  and  which  is  bleached  on 
the  addition  of  a  solution  of  mercuric  chloride  (HgClJ. 

Rate  of  Secretion  and  Quantity. — The  rate  at  which  saliva  is 
secreted  is  subject  to  considerable  variation.  When  the  tongue  and 
muscles  concerned  in  mastication  are  at  rest,  and  the  nerves  of  the  mouth 
are  subject  to  no  unusual  stimulus,  the  quantity  secreted  is  not  more  than 
sufficient,  with  the  mucus,  to  keep  the  mouth  moist.  During  actual 
secretion  the  flow  is  much  accelerated. 

The  quantity  secreted  in  twenty-four  hours  varies;  its  average  amount 
is  probably  from  1  to  3  pints  (1  to  2  litres). 

Uses  of  Saliva. — The  purposes  served  by  saliva  are  (1)  mechanical  and 
(2)  chemical.  I.  Mechanical. — (1)  It  keeps  the  mouth  in  a  due  condition 
of  moisture,  facilitating  the  movements  of  the  tongue  in  speaking,  and 
the  mastication  of  food.  (2)  It  serves  also  in  dissolving  sapid  substances, 
and  rendering  them  capable  of  exciting  the  nerves  of  taste.  But  the 
principal  mechanical  purpose  of  the  saliva  is,  (3)  that  by  mixing  with  the 
food  during  mastication,  it  makes  it  a  soft  pulpy  mass,  such  as  may  be 
easily  swallowed.  To  this  purpose  the  saliva  is  adapted  both  by  quantity 
and  quality.  For,  speaking  generally,  the  quantity  secreted  during  feed- 
ing is  in  direct  proportion  to  the  dryness  and  hardness  of  the  food.  The 
quality  of  saliva  is  equally  adapted  to  this  end.  It  is  easy  to  see  how 
much  more  readily  it  mixes  with  most  kinds  of  food  than  water  alone 
does;  and  the  saliva  from  the  parotid,  labial,  and  other  small  glands, 
being  more  aqueous  than  the  rest,  is  that  which  is  chiefly  braided  and 
mixed  with  the  food  in  mastication;  while  the  more  viscid  mucous  secre- 
tion of  the  submaxillary,  palatine,  and  tonsillitic  glands  is  spread  over 
the  surface  of  the  softened  mass,  to  enable  it  to  slide  more  easily  through 
the  fauces  and  oesophagus.  II.  Chemical. — Saliva  has  the  power  of  con- 
verting starch  into  glucose  or  grape-sugar.  When  saliva,  or  a  portion  of 
a  salivary  gland,  is  added  to  starch  paste  in  a  test-tube,  and  the  mixture 
kept  at  a  temperature  of  100°  F.  (37 '8°  C),  the  starch  is  very  rapidly 
transformed  into  grape-sugar.  There  is  an  intermediate  stage  in  which  a 
part  or  the  whole  of  the  starch  becomes  dextrin. 

Test  for  Glucose. — In  such  an  experiment  the  presence  of  sugar  is  at 
once  discovered  by  the  application  of  Ti'onimer's  tost,  which  consists  in 
tlie  addition  of  a  drop  or  two  of  a  solution  of  copper  su]})liate,  followed 
by  a  larger  qiuintity  of  caustic  potash.  When  the  liquid  is  boiled,  an 
orange-red  ])reci})itate  of  coi)])er  suboxide  indicates  the  presence  of  sugar; 
and  when  common  raw  starch  is  masticated  and  mingled  with  saliva,  and 
kept  with  it  at  a  temperature  of  00°  or  100°  F.  (30°— 37.8°  C),  the 
Ktar(;h-grains  are  crac^ked  or  eroded,  and  tlieir  contents  are  transformed 
in  the  Raiiu;  manner  as  the  starch-i)aste. 


DIGESTION. 


281 


Saliva  from  the  parotid  is  less  viscid,  less  alkaline,  clearer,  and  more 
watery  than  that  from  the  submaxillary.  It  has,  moreover,  a  less  power- 
ful action  on  starch.  Sublingual  saliva  is  the  most  viscid,  and  contains 
more  solids  than  either  of  the  other  two,  but  does  not  appear  to  be  so 
powerful  in  its  action. 

The  salivary  glands  of  children  do  not  become  functionally  active  till 
the  age  of  4  to  6  months,  and  hence  the  bad  effect  of  feeding  them  before 
this  age  on  starchy  food,  corn-flour,  etc.,  which  they  are  unable  to  render 
soluble  and  capable  of  absorption. 

Action  of  Saliva  on  Starch. — This  action  is  due  to  the  presence 
in  the  saliva  of  the  body  called  ptyalin.  It  is  a  nitrogenous  body,  and 
belongs  to  the  order  of  ferments,  which  are  bodies  whose  exact  chemical 
composition  is  unknown,  and  which  are  capable  of  producing  by  their 
presence  changes  in  other  bodies,  withoat  themselves  undergoing  change. 
Ptyalin  is  called  a  liydrolytic  ferment,  that  is  to  say,  it  acts  by  adding  a 
molecule  of  water  to  the  body  changed.  The  reaction  is  supposed  to  be 
as  follows: 

3  C,H,.0.  +  3  H,0  =  +  3  (C,H,.0.)  +  3  H,0  =  3  C.H.,0,. 

Starch      +  Water.       Glucose  Dextrin  Glucose 

But  it  is  not  unlikely  that  the  action  is  by  no  means  so  simple.  la 
the  first  place,  recent  observers  believe  that  a  molecule  of  starch  must  be 
represented  by  a  much  more  complex  formula;  next,  that  the  stages  in 
the  reaction  are  more  numerous  and  extensive;  and  thirdly,  that  the  pro- 
duct of  the  reaction  is  not  true  glucose,  but  maltose.  Maltose  is  a  sugar 
more  akin  to  cane  than  grape  sugar,  of  very  little  sweetening  power,  and 
with  less  reducing  power  over  copper  salts.    Its  formula  is  G^^^fi^^. 

The  action  of  saliva  on  starch  is  facilitated  by:  {a)  Moderate  heat, 
about  100°  F.  (37-8°  C).  {h)  A  slightly  alkaline  medium,  {c)  Kemoval 
of  the  changed  material  from  time  to  timiC.  Its  action  is  retarded  by:  {a) 
Cold;  a  temperature  of  32°  F.  (0°  C.)  stops  it  for  a  time,  but  does  not 
destroy  it,  whereas  a  high  temperature  above  140°  F.  (60°  C.)  destroys 
it.  (h)  Acids  or  strong  alkalies  either  delay  or  stop  the  action  altogether, 
(c)  Presence  of  too  much  of  the  changed  material.  Ptyalin,  in  that  it 
converts  starch  into  sugar,  is  an  amylolytic  ferment. 

Starch  appears  to  be  the  only  principle  of  food  upon  which  saliva  acts 
chemically:  it  has  no  apparent  influence  on  any  of  the  other  ternary  prin- 
ciples, such  as  sugar,  gum,  cellulose,  or  on  fat,  and  seems  to  be  equally 
destitute  of  power  over  albuminous  and  gelatinous  substances. 

Influence  of  the  Nervous  System. — The  secretion  of  saliva  is 
under  the  control  of  the  nervous  system.  It  is  a  reflex  action,  and  in 
ordinary  conditions  is  excited  by  the  stimulation  of  the  peripheral 
branches  of  two  nerves,  viz.,  the  gustatory  or  lingual  branch  of  the  in- 


232 


HAND-BOOK  OF  PHYSIOLOGY. 


f erior  maxillary  division  of  the  fifth  nerve,  and  the  glosso-pharyiigeal  part 
of  the  eighth  pair  of  nerves,  which  are  distributed  to  the  mucous  mem- 
brane of  the  tongue  and  pharynx.  The  stimulation  occurs  on  the  intro- 
duction of  sapid  substances  into  the  mouth,  and  the  secretion  is  brought 
about  in  the  following  way.  From  the  terminations  of  these  sensory 
nerves,  in  the  mucous  membrane  an  impression  is  conveyed  upward  (affer- 
ent) to  the  special  nerve  centre  situated  in  the  medulla,  which  controls 
the  process,  and  by  it  is  reflected  to  certain  nerves  sujoplied  to  the  salivary 
glands,  which  will  be  presently  indicated.  In  other  words,  the  centre, 
stimulated  to  action  by  the  sensory  impressions  carried  to  it,  sends  out 
impulses  alons^  efferent  or  secretory  nerves  supplied  to  the  salivary  glands, 
which  cause  the  saliva  to  be  secreted  by  and  discharged  from  the  gland 
cells.  Other  stimuli,  however,  besides  that  of  the  food,  and  other  sensory 
nerves  besides  those  mentioned,  may  produce  reflexly  the  same  effects. 
Saliva  may  be  caused  to  flow  by  irritation  of  the  mucous  membrane  of  the 
mouth  with  mechanical,  chemical,  electrical,  or  thermal  stimuli,  also  by 
the  irritation  of  the  mucous  membrane  of  the  stomach  in  some  way,  as  in 
nausea,  which  precedes  vomiting,  when  some  of  the  peripheral  fibres  of 
the  vagi  are  irritated.  Stimulation  of  the  olfactory  nerves  by  smell  of 
food,  of  the  optic  nerves  by  the  sight  of  it,  and  of  the  auditory  nerves 
by  the  sounds  which  are  known  by  experience  to  accompany  the  prejja- 
i^tion  of  a  meal,  may  also,  in  the  hungry,  stimulate  the  nerve  centre  to 
action.  In  addition  to  these,  as  a  secretion  of  saliva  follows  the  move- 
ment of  the  muscles  of  mastication,  it  may  be  assumed  that  this  move- 
ment stimulates  the  secreting  nerve  fibres  of  the  gland,  directly  or  re- 
flexly. From  the  fact  that  the  flow  of  saliva  may  be  increased  or  dimin- 
ished by  mental  emotions,  it  is  evident  that  impressions  from  the  cere- 
brum also  are  capable  of  stimulating  the  centre  to  action  or  of  inhibiting 
its  action. 

Secretion  may  be  excited  by  direct  stimulation  of  the  centre  in  the 
medulla. 

A.  On  the  Submaxillary  Gland. — The  submaxillary  gland  has  been 
the  gland  chiefly  employed  for  the  purpose  of  experimentally  demonstra- 
ting the  influence  of  the  nervous  system  upon  the  secretion  of  saliva,  be- 
cause of  the  comparative  facility  with  which,  with  its  blood-vessels  and 
nerves,  it  may  be  exposed  to  view  in  the  dog,  rabbit,  and  other  animals. 
The  chief  nerves  supplied  to  the  gland  are:  (1)  the  cliorda  tympani  (a 
branch  given  off*  from  facial  portio  dura  of  the  seventh  pair  of  nerves), 
in  the  canal  through  which  it  passes  in  the  temporal  bone,  in  its  passage 
from  the  interior  of  the  skull  to  the  face;  and  (2)  branches  of  the  sym- 
pathetic nerve  from  the  plexus  arouiul  the  facial  artery  jiiul  its  branches 
to  the  gland.  The  chorda  (Fig.  170,  ch.  /.),  after  quitting  the  temporal 
bone,  passes  downward  and  forwiird,  under  cover  of  the  extornnl  pterygoid 
muscle,  and  joins  at  an  acute  angle  the  lingual  or  gustatory  nerve,  pro- 


DIGESTION. 


233 


ceeds  with  it  for  a  short  distance,  and  then  passes  along  the  submaxillary 
gland  duct  (Fig.  170,  sm.  d.),  to  which  it  is  distributed,  giving  branches 
to  the  submaxillary  ganglion  (Fig.  170,  S7n.  gl.),  and  sending  others  to 
terminate  in  the  superficial  muscle  of  the  tongue.  If  this  nerve  be  exposed 
and  divided  anywhere  in  its  course  from  its  exit  from  the  skull  to  the 
gland,  the  secretion,  if  the  gland  be  in  action,  is  arrested,  and  no  stimu- 
lation either  of  the  lingual  or  of  the  glosso-pharyngeal  will  produce  a  flow 
of  saliva.  But  if  the  peripheral  end  of  the  divided  nerve  be  stimulated, 
an  abundant  secretion  of  saliva  ensues,  and  the  blood  supply  is  enormously 


Fig.  170. — Diagrammatic  representation  of  the  submaxillary  gland  of  the  dog  with  its  nerves  and 
blood-vessels.  (This  is  not  intended  to  illustrate  the  exact  anatomical  relations  of  the  several  struct- 
ures.) sm.  gld.,  the  submaxillary  gland  into  the  duct  (sm.  d.),  of  which  a  cannula  has  been  tied. 
The  subhngual  gland  and  duct  are  not  shown,  n.l.,  n.l'.,  the  lingual  or  gustatory  nerve ;  ch.  t.,  ch.  t'., 
the  chorda  tympani  proceeding  from  the  facial  nerve,  becoming  conjoined  with  the  lingual  at  n.  1'., 
and  afterward  diverging  and  passing  to  the  gland  along  the  duct;  snt.  gl..  submaxillary  ganglion 
with  its  roots;  n.  Z.,  the  hngual  nerve  proceeding  to  the  tongue;  a.  car..,  the  carotid  artery,  two 
branches  of  which,  a.  sm.  a.  and  r.  sm.  p.,  pass  to  the  anterior  and  posterior  parts  of  the  gland;  v. 
sm.,  the  anterior  and  posterior  veins  from  the  gland  ending  in  v.  j.,  the  jugular  vein;  v.  sym.,  the  con- 
joined vagus  and  sympathetic  trunks;  gl.  cer.  .s.,  the  superior-ceiwical  ganglion,  two  branches  of  which 
forming  a  plexus,  a.  /.,  over  the  facial  artery  are  distributed  (n.  sym.  sm.)  along  the  two  glandular 
arteries  to  the  anterior  and  posterior  portion  of  the  gland.  The  arrows  indicate  the  direction  taken 
by  the  nervous  impulses ;  during  reflex  stimulations  of  the  gland  they  ascend  to  the  brain  by  the  lin- 
gual and  descend  by  the  chorda  tympani.    (M.  Foster.) 


increased,  the  arteries  being  dilated.  The  veins  even  pulsate,  and  the 
blood  contained  within  them  is  more  arterial  than  venous  in  character. 

When,  on  the  other  hand,  the  stimulus  is  applied  to  the  sympathetic 
filaments  (mere  division  producing  no  apparent  effect),  the  arteries  con- 
tract, and  the  blood  stream  is  in  consequence  much  diminished;  and  from 
the  veins,  when  opened,  there  escapes  only  a  sluggish  stream  of  dark 
blood.  The  saliva,  instead  of  being  abundant  and  watery,  becomes  scanty 
and  tenacious.  If  both  chorda  tympani  and  sympathetic  branches  be  di- 
vided, the  gland,  released  from  nervous  control,  secretes  continuously  and 
abundantly  (paralytic)  secretion. 

The  abundant  secretion  of  saliva,  which  follows  stimulation  of  the 


234 


HAND-BOOK  OF  PHYSIOLOGY. 


chorda  tympani,  is  not  merely  the  result  of  a  filtration  of  fluid  from  the 
blood-vessels,  in  consequence  of  the  largely  increased  circulation  through 
them.  This  is  proved  by  the  fact  that,  when  the  main  duct  is  obstructed, 
the  pressure  within  may  considerably  exceed  the  blood-pressure  in  the 
arteries,  and  also  that  when  into  the  veins  of  the  animal  experimented 
upon  some  atropin  has  been  previously  injected,  stimulation  of  the 
peripheral  end  of  the  divided  chorda  produces  all  the  vascular  effects  as 
before,  without  any  secretion  of  saliva  accompanying  them.  Again,  if 
an  animal's  head  be  cut  off,  and  the  chorda  be  rapidly  exposed  and  stimu- 
lated with  an  interrupted  current,  a  secretion  of  saliva  ensues  for  a  short 
time,  although  the  blood  supply  is  necessarily  absent.  These  experiments 
serve  to  prove  that  the  chorda  contains  two  sets  of  nerve  fibres,  one  set 
{vaso-dilator')  which,  when  stimulated,  act  upon  a  local  vaso-motor  centre 
for  regulating  the  blood  supply,  inhibiting  its  action,  and  causing  the 
vessels  to  dilate,  and  so  producing  an  increased  supply  of  blood  to  the 
gland;  while  another  set,  which  are  paralyzed  by  injection  of  atropin, 
directly  stimulate  the  cells  themiselves  to  activity,  whereby  they  secrete 
and  discharge  the  constituents  of  the  saliva  which  they  produce.  These 
latter  fibres  very  possibly  terminate  in  the  salivary  cells  themselves.  If, 
on  the  other  hand,  the  sympathetic  fibres  be  divided,  stimulation  of  the 
tongue  by  sapid  substances,  or  of  the  trunk  of  the  lingual,  or  of  the  glosso- 
pharyngeal, continues  to  produce  a  flow  of  saliva.  From  these  experi- 
ments it  is  evident  that  the  chorda  tympani  nerve  is  the  principal  nerve 
through  which  efferent  impulses  proceed  from  the  centre  to  excite  the 
secretion  of  this  gland. 

The  sympathetic  fibres  appear  to  act  principally  as  a  vaso-constrictor 
nerve,  and  to  exalt  the  action  of  the  local  vaso-motor  centres.  The 
sympathetic  is  more  powerful  in  this  direction  than  the  chorda.  There 
is  not  sufficient  evidence  in  favor  of  the  belief  that  the  submaxillary  gan- 
glion is  ever  the  nerve  centre  which  controls  the  secretion  of  the  sub- 
maxillary gland. 

B.  On  the  Parotid  Gland. — The  nerves  which  influence  secretion  in 
the  parotid  gland  are  branches  of  the  facial  (lesser  superficial  petrosal)  and 
of  the  sympathetic.  The  former  nerve,  after  passing  through  the  otic 
ganglion,  joins  the  auriculo-temporal  branch  of  the  fiftli  cerebral  nerve, 
and,  with  it,  is  distributed  to  the  gland.  The  nerves  by  which  the  stimu- 
lus ordinarily  exciting  secretion  is  conveyed  to  tlie  medulla  oblongata,  are, 
as  in  the  case  of  the  submaxillary  gland,  the  fifth,  and  the  glossopharyn- 
geal, '^i'he  piu'iimogastric  nerves  convey  a  further  stimulus  to  the  secre- 
tion of  saliva,  wlien  food  has  entered  the  stomach;  the  nerve  centre  is  the 
same  as  in  the  case  of  the  submaxilbiry  gland. 

Changes  in  the  Gland  Cells. — The  method  by  which  the  salivary 
cells  produce  the  secretion  of  saliva  appears  to  be  divided  intt)  two  stages, 
whi(;li  dilTer  somewhat  according  to  the  class  to  which  the  gland  belongs, 


DIGESTION. 


235 


viz.,  (1)  the  true  salivary,  or  (2)  the  mucous  type.  In  the  former  case, 
it  has  been  noticed,  as  has  been  already  described  (p.  228),  that  during 
the  rest  which  follows  an  active  secretion  the  lumen  of  the  alveoli  be- 
comes smaller,  the  gland  cells  larger,  and  very  granular.  During  secre- 
tion the  alveoli  and  their  cells  become  smaller,  and  the  granular  appear- 
ance in  the  latter  to  a  considerable  extent  disappears,  and  at  the  end  of 
secretion,  the  granules  are  confined  to  the  inner  part  of  the  cell  nearest 
to  the  lumen,  which  is  now  quite  distinct  (Fig.  171). 

It  is  supposed  from  these  appearances  that  the  first  stage  in  the  act  of 
secretion  consists  in  the  protoplasm  of  the  salivary  cell  taking  up  from 
the  lymph  certain  materials  from  which  it  manufactures  the  elements  of 
its  own  secretion,  and  which  are  stored  up  in  the  form  of  granules  in  the 
cell  during  rest,  the  second  stage  consisting  of  the  actual  discharge  of 


Fig.  171.— Alveoli  of  true  salivary  gland.  A,  at  rest;  B,  in  the  first  stage  of  secretion;  C,  after 
prolonged  secretion.  (Langley.) 

these  granules,  with  or  without  previous  change.  The  granules  are  taken 
to  represent  the  chief  substance  of  the  salivary  secretion,  i.e.,  the  ferment 
ptyalin.  In  the  case  of  the  submaxillary  gland  of  the  dog,  at  any  rate, 
the  sympathetic  nerve-fibres  appear  to  have  to  do  with  the  first  stage  of 
the  process,  and  when  stimulated  the  protoplasm  is  extremely  active  in 
manufacturing  the  granules,  whereas  the  chorda  tympani  is  concerned  in 
the  production  of  the  second  act,  the  actual  discharge  of  the  materials  of 
secretion,  together  with  a  considerable  amount  of  fluid,  the  latter  being 
an  actual  secretion  by  the  protoplasm,  as  it  ceases  to  occur  when  atropin 
has  been  subcutaneously  injected. 

In  the  mucous-secreting  gland,  the  changes  in  the  cells  during  secre- 
tion have  been  already  spoken  of  (p.  228).  They  consist  in  the  gradual 
secretion  by  the  protoplasm  of  the  cell  of  a  substance  called  mucigeyiy 
which  is  converted  into  mucin,  and  discharged  on  secretion  into  the  canal 
of  the  alveoli.  The  mucigen  is,  for  the  most  part,  collected  into  the 
inner  part  of  the  cells  during  rest,  pressing  the  nucleus  and  the  small 
portion  of  the  protoplasm  which  remains,  against  the  limiting  membrane 
of  the  alveoli. 

The  process  of  secretion  in  the  salivary  glands  is  identical  with  that  of 
glands  in  general;  the  cells  which  line  the  ultimate  branches  of  the  ducts 
being  the  agents  by  which  the  special  constituents  of  the  saliva  are  formed. 


236 


HAND-BOOK  OF  PHYSIOLOGY. 


The  materials  which  they  have  incorporated  with  themselves  are  almost 
at  once  given  up  again ^  in  the  form  of  a  fluid  (secretion),  which  escapes 
from  the  ducts  of  the  gland;  and  the  cells,  themselves,  undergo  disinte- 
gration,— again  to  be  renewed,  in  the  intervals  of  the  active  exercise  of 
their  functions.  The  source  whence  the  cells  obtain  the  materials  of 
their  secretion,  is  the  blood,  or,  to  speak  more  accurately,  the  plasma, 
which  is  filtered  off  from  the  circulating  blood  into  the  interstices  of  the 
glands  as  of  all  living  textures. 

The  Pharynx. 

That  portion  of  the  alimentary  canal  which  intervenes  between  the 
mouth  and  the  oesophagus  is  termed  the  Pharynx  (Fig.  165).  It  will 
suffice  here  to  mention  that  it  is  constructed  of  a 
series  of  three  muscles  with  striated  fibres  {const rict- 
ors),  which  are  covered  by  a  thin  fascia  externally, 
and  are  lined  internally  by  a  strong  fascia  (pharyn- 
geal aponeurosis),  on  the  inner  aspect  of  which  is 
areolar  (submucous)  tissue  and  mucous  membrane, 
continuous  with  that  of  the  mouth,  and,  as  regards 
the  part  concerned  in  swallowing,  is  identical  with 
Fig.  172.— Lingual  foi-  general  structure.    The  epithelium  of  this  part 

tion''of''^ucoSs'mem-        the  pharynx,  like  that  of  the  mouth,  is  stratified 

brane  with  its  papillae;  r^-^A  onnommi? 
6,  lymphoid  tissue,  with  SquamOUS. 

t^tj^  ^^'^P^'"'*^  The  pharynx  is  well  supplied  with  mucous  glands 

(Fig.  174). 

The  Tonsils. — Between  the  anterior  and  posterior  arches  of  the  soft 
palate  are  situated  the  Tonsils,  one  on  each  side.  A  tonsil  consists  of  an 
elevation  of  the  mucous  membrane  presenting  12  to  15  orifices,  which  lead 
into  cryj)ts  or  recesses,  in  the  walls  of  Avhich  are  placed  nodules  of  adenoid 
or  lymphoid  tissue  (Fig.  173).  These  nodules  are  enveloped  in  a  less 
dense  adenoid  tissue  which  reaches  the  mucous  surface.  T]ie  surface  is 
covered  with  stratified  squamous  epithelium,  and  the  subepithelial  or 
mucous  membrane  proj^er  may  present  rudimentary  papilla^  formed  of 
adenoid  tissue.  The  tonsil  is  bounded  by  a  fibrous  capsule  (Fig.  173,  e). 
Into  the  crypts  open  a  number  of  ducts  of  mucous  glands. 

The  viscid  secretion  wliich  exudes  from  the  tonsils  serves  to  lubricate 
tlie  bolus  of  food  as  it  passes  them  in  the  second  part  of  the  act  of  degluti- 
tion. 

The  (Esophagus  or  Gullet. 

Tlie  (Esophagux  or  Gullet  (Fig.  1G5),  the  narrowest  portion  of  the 
alimentary  canal,  is  a  muscular  and  mucous  tube,  nine  or  ten  inclies  in 
louirtli,  which  extends  from  the  lower  end  of  the  pharvnx  to  tho  cardiac 
orilice  of  tlie  stomach. 


DIGESTION. 


237 


structure. — The  oesophagus  is  made  up  of  three  coats — viz.,  the  outer, 
muscular';  the  middle,  suhnucoiis;  and  the  inner,  mucous.  The  mus- 
cular coat  (Fig.  175,  g  and  i)  is  covered  externally  by  a  varying  amount 
of  loose  fibrous  tissue.  It  is  composed  of  two  layers  of  fibres,  the  outer 
being  arranged  longitudinally,  and  the  inner  circularly.  At  the  upper 
part  of  the  oesophagus  this  coat  is  made  up  principally  of  striated  muscle 
fibres,  as  they  are  continuous  with  the  constrictor  muscles  of  the  pharynx; 
but  lower  down  the  unstriated  fibres  become  more  and  more  numerous,  and 
toward  the  end  of  the  tube  form  the  entire  coat.  The  muscular  coat  is 
connected  with  the  mucous  coat  by  a  more  or  less  developed  layer  of 


Fig.  173.— Vertical  section  through  a  crypt  of  the  hiiman  tonsil,  a,  entrance  to  the  crypt,  -which 
is  divided  below  by  the  elevation  which  does  not  quite  reach  the  surface;  6,  stratified  epithehum;  c, 
masses  of  adenoid  tissue;  d,  mucous  glands  cut  across;  e,  fibrous  capsule.   (V.  D.  Harris.) 

areolar  tissue,  which  forms  the  submucous  coat  (Fig  175,/),  in  which  is 
contained  in  the  lower  half  or  third  of  the  tube  many  mucous  glands,  the 
ducts  of  which,  passing  through  the  mucous  membrane  (Fig.  175,  c)  open 
on  its  surface.  Separating  this  coat  from  the  mucous  membrane  proper 
is  a  well-developed  layer  of  longitudinal,  unstriated  muscle  (d),  called 
the  muscularis  miicosce.  The  mucous  membrane  is  composed  of  a  closely 
felted  meshwork  of  fine  connective  tissue,  which,  toward  the  surface,  is 
elevated  into  rudimentary  papillae.  It  is  covered  with  a  stratified  epithe- 
lium, of  which  the  most  superficial  layers  are  squamous.  The  epithelium 
is  arranged  upon  a  basement  membrane. 

In  newly-born  children  the  mucous  membrane  exhibits,  in  many  parts, 
the  structure  of  lymphoid  tissue  (Klein). 

Blood  and  lymph  vessels,  and  nerves,  are  distributed  in  the  walls  of 
the  oesophagus.  Between  the  outer  and  inner  layers  of  the  muscular  coat, 
nerve-ganglia  of  Auerbach  are  also  found. 


238 


HAIsD-BOOK  OF  PHYSIOLOGY. 


Deglutitiox  oe  Swallowing. 

When  properly  masticated,  the  food  is  transmitted  in  successive  por- 
tions to  the  stomach  by  the  act  of  deglutition  or  sicaUoicing.  This,  for 
the  purpose  of  description,  may  be  divided  into  tliree  acts.  In  the  first, 
particles  of  food  collected  to  a  morsel  are  made  to  glide  between  the  sur- 
face of  the  tongue  and  the  palatine  arch,  till  they  have  passed  the  anterior 
arch  of  the  fauces;   in  the  second,  the  morsel  is  carried  through  the 


Fig.  174.  -  Fig.  175. 


Fig.  174.— Section  of  a  mucous  gland  from  thetongrie.  A.  opening  of  the  duct  on  the  free  sur- 
face; C,  basement  membrane  with  nuclei;  B,  flattened  epithelial  cells  lining  duct.  The  duct  divides 
into  several  branches,  which  are  convoluted  and  end  blindly,  being  lined  throughout  by  colmnnar 
epitheUum.    D,  lumen  of  one  of  tlie  tubuli  of  the  gland,    x  iK).    (Klein  and  Noble  Smith.)" 

Fig.  17.5. — Longitudinal  section  of  oesophagus  of  a  dog  toward  the  lower  end.  n.  stratified  epithe- 
lium of  the  mucous  mend^rane;  h.  mucous  mend)rane  proper;  c,  iluct  of  nuicous  gland;  rf.  nuiscu- 
laris  mucosfe ;  c,  nuicous  glands;  /,  submucous  coat ;  circular  nmscular  layer;  /(.  intermuscular 
laj-er,  in  which  is  contained  the  ganglion  cells  of  Auerbach;  /,  longituilinal  nmscular  layer;  outside 
investment  of  fibrous  tissue.    X  100.  (.V.D.Harris.) 

pharynx;  and  in  the  third,  it  readies  tlie  stomach  tlirough  tlie  opsopha2:us. 
These  three  acts  follow  each  otlicr  rapidly.  (1.)  The  first  act  of  deghitition 
may  be  voluntary,  although  it  is  usually  performed  unconsciously;  tlie 
morsel  of  food,  wlien  sufficiently  masticated,  being  pressed  between  the 
tongue  and  palate,  by  the  agency  of  the  muscles  of  the  former,  in  such 
a  manner  as  to  force  it  back  to  the  entrance  of  tlie  pharynx,  {"l.)  The 
second  act  is  tlie  most  complicated,  because  the  food  must  pass  by  the 


I 


DIGESTION.  239 

posterior  orifice  of  the  nose  and  the  upper  opening  of  tlic  krynx  witliout 
touching  them.  When  it  has  been  brought,  by  the  first  act,  between  the 
anterior  arches  of  the  pahite,  it  is  moved  onward  by  the  movement  of 
the  tongue  backward,  and  by  the  muscles  of  the  anterior  arches  contract- 
ing on  it  and  then  behind  it.  The  root  of  the  tongue  being  retracted, 
and  the  larynx  being  raised  with  the  pharynx  and  carried  forward  under 
the  base  of  the  tongue,  the  epiglottis  is  pressed  over  the  upper  opening 
of  the  larynx,  and  the  morsel  glides  past  it;  the  closure  of  the  glottis 
being  additionally  secured  by  the  simultaneous  contraction  of  its  own  mus- 
cles: so  that,  even  when  the  epiglottis  is  destroyed,  there  is  little  danger 
of  food  or  drink  passing  into  the  larynx  so  long  as  its  muscles  can  act 
freely.  At  the  same  time,  the  raising  of  the  soft  palate,  so  that  its  pos- 
terior edge  touches  the  back  part  of  th.e  pharynx,  and  the  approximation 
of  the  sides  of  the  posterior  palatine  arch,  which  move  quickly  inward 
like  side  curtains,  close  the  passage  into  the  upper  part  of  the  pharynx  and 
the  posterior  nares,  and  form  an  inclined  plane,  along  the  under  surface 
of  which  the  morsel  descends;  then  the  pharynx,  raised  up  to  receive  it, 
in  its  turn  contracts,  and  forces  it  onward  into  the  oesophagus.  (3.)  In 
the  third  act,  in  which  the  food  passes  through  the  oesophagus,  every 
part  of  that  tube,  as  it  receives  the  morsel  and  is  dilated  by  it,  is  stimu- 
lated to  contract:  hence  an  undulatory  contraction  of  the  oesophagus, 
which  is  easily  observable  in  horses  while  drinking,  proceeds  rapidly  along 
the  tube.  It  is  only  when  the  morsels  swallowed  are  large,  or  taken  too 
quickly  in  succession,  that  the  progressive  contraction  of  the  oesophagus 
is  slow,  and  attended  with.  pain.  Division  of  both  pneumogastric  nerves 
paralyzes  the  contractile  power  of  the  oesophagus,  and  food  accordingly 
accumulates  in  the  tube.  The  second  and  third  parts  of  the  act  of  deglu- 
tition are  involuntary. 

Nerve  Mechanism. — The  nerves  engaged  in  the  reflex  act  of  deglu- 
tition are: — sensory,  branches  of  the  fiith  cerebral  supplying  the  soft 
palate;  glosso-pharyngeal,  supplying  the  tongue  and  pharynx;  the  supe- 
rior laryngeal  branch  of  the  vagus,  supplying  the  epiglottis  and  the  glot- 
tis; while  the  motor  fibres  concerned  are: — branches  of  the  fifth,  supply- 
ing part  of  the  digastric  and  mylo-hyoid  muscles,  and  the  muscles  of 
mastication;  the  facial,  supplying  the  levator  palati;  the  glosso-pharyn- 
geal, supplying  the  muscles  of  the  pharynx;  the  vagus,  supplying  the 
muscles  of  the  larynx  through  the  inferior  laryngeal  branch,  and  the 
hypoglossal,  the  muscles  of  the  tongue.  The  nerve-centre  by  which 
the  muscles  are  harmonized  in  their  action,  is  situate  in  the  medulla 
oblongata.  In  the  movements  of  the  oesophagus,  the  ganglia  contained 
in  its  walls,  with  the  pneumogastrics,  are  the  nerve-structures  chiefly 
concerned. 

It  is  important  to  note  that  the  swallowing  both  of  food  and  drink  is  a 
muscular  act,  and  can,  therefore,  take  place  in  opposition  to  the  force  of 


240 


HAND-BOOK  OF  PHYSIOLOGY. 


gravity.  Tlius,  horses  and  many  other  animals  habitually  drink  up-hill, 
and  the  same  feat  can  be  performed  by  jugglers. 

The  Stomach. 

In  man  and  those  Mammalia  which  are  provided  with  a  single  stomach, 
it  consists  of  a  dilatation  of  the  alimentary  canal  placed  between  and  con- 
tinuous with  the  oesophagus,  which  enters  its  larger  or  cardiac  end  on  the 
one  hand,  and  the  small  intestine,  which  commences  at  its  narrowed  end 
or  pylorus,  on  the  other.  It  varies  in  shape  and  size  according  to  its 
state  of  distension. 

The  Ruminants  (ox,  sheep,  deer,  etc.)  possess  very  complex  stomachs; 
in  most  of  them  four  distinct  cavi£ies  are  to  be  distinguished  (Fig  176). 

1.  The  Pauncli  or  Rumen,  a  very  large  cavity  which  occupies  the  car- 
diac end,  and  into  which  large  quantities  of  food  are  in  the  first  instance 
swallowed  Avitli  little  or  no  mastication.  2.  The  Reticulum,  or  Honey- 
coiiib  stomach,  so  called  from  the  fact  that  its  mucous  membrane  is  dis- 
posed in  a  number  of  folds  enclosing  hexagonal  cells.  3.  The  Psalteriumy 


Fig.  176.— Stomach  of  sheep,  ce,  oesophagus;  Ru,  rumen;  Ret,  reticulum;  Ps,  psalteriimi,  or 
manypUes;  A,  abomasum;  Du,  duodemun;  g,  groove  from  oesophagus  to  psalterium.  (Huxley.) 

or  ManypUes,  in  which  the  mucous  membrane  is  arranged  in  very  promi- 
nent longitudinal  folds.  4.  Aliomasum.,  Reed,  or  Rennet,  narrow  and 
elongated,  its  mucous  membrane  being  much  more  highly  vascular  than 
that  of  the  other  divisions.  In  the  process  of  rumination  small  portions 
of  the  contents  of  the  rumen  and  reticulum  are  successively  regurgitated 
into  the  mouth,  and  there  tlioroughly  masticated  and  insalivated  (chew- 
ing the  cud):  they  are  then  again  swallowed,  being  this  time  directed  by 
a  groove  (which  in  the  figure  is  seen  running  from  the  lower  end  of  the 
oesophagus)  into  the  manyplics,  and  thence  into  the  abomasum.  It  will 
thus  1)0  seen  that  the  first  two  stomachs  (paunch  and  reticulum)  have 
chiefly  the  mechanical  functions  of  storing  and  moistening  the  fodder:  the 
tliird  (manyplies)  probably  acts  as  a  strainer,  only  allowing  the  finely  , 
divided  portions  of  food  to  pass  on  into  the  fourth  stomach,  where  the 
gastric  juice  is  secreted  and  the  process  of  digestion  carried  on.  The 
mncous  membrane  of  the  first  three  stomachs  is  lowly  vascular,  while  that 
of  the  fonrth  is  pulpy,  ghmduhir,  aiul  highly  vascular. 

In  some  other  aniinaJs,  as  t  he  pig,  a  similar  distinction  obtains  between 
the  mucous  membrane  in  ditl'erent  parts  of  the  stomach. 


DIGESTION. 


241 


In  the  pig  the  glands  in  the  cardiac  end  are  few  and  small,  while 
toward  the  pylorus  they  arc  abundant  and  large. 

A  similar  division  of  the  stomach  into  a  cardiac  (receptive)  and  a 
pyloric  (digestive)  part,  foreshadowing  the  complex  stomach  of  rumi- 
nants, is  seen  in  the  common  rat,  in  which  these  two  divisions  of  the 
stomach  are  distinguished,  not  only  by  the  characters  of  their  lining 
membrane,  but  also  by  a  well-marked  constriction. 

In  birds  the  function  of  mastication  is  performed  by  the  stomach  (giz- 
zard) which  in  granivorous  orders,  e.g.  the  common  fowl,  possesses  very 
powerful  muscular  walls  and  a  dense  horny  epithelium. 

Structure. — The  stomach  is  composed  of  four  coats,  called  respec- 
tively— an  external  or  (1)  peritoneal,  (2)  muscular,  (3)  suhnucous,  and 
(4)  mucous  coat;  with  blood-vessels,  lymphatics,  and  nerves  distributed  in 
and  between  them. 

(1)  The  peritoneal  coat  has  the  structure  of  serous  membranes  in  gen- 
eral (p.  319).  (1)  The  muscular  coat  consists  of  three  separate  layers  or 
sets  of  fibres,  which,  according  to  their  several  directions,  are  named  the 
longitudinal,  circular,  and  oblique.  The  loiigitudinal  set  are  the  most 
superficial:  they  are  continuous  with  the  longitudinal  fibres  of  the  oesoph- 
agus, and  spread  out  in  a  diverging  manner  aver  the  cardiac  end  and 
sides  of  the  stomach.  They  extend  as  far  as  the  pylorus,  being  especially 
distinct  at  the  lesser  or  upper  curvature  of  the  stomach,  along  which 
they  pass  in  several  strong  bands.  The  next  set  are  the  circular  or  trans- 
verse fibres,  which  more  or  less  completely  encircle  all  parts  of  the 
stomach;  they  are  most  abundant  at  the  middle  and  in  the  pyloric  portion 
of  the  organ,  and  form  the  chief  part  of  the  thick  projecting  ring  of  the 
pylorus.  These  fibres  are  not  simple  circles,  but  form  double  or  figure- 
of-8  loops,  the  fibres  intersecting  very  obliquely.  The  next,  and  con- 
sequently deepest  set  of  fibres,  are  the  oblique,  continuous  with  the  cir- 
cular muscular  fibres  of  the  oesophagus,  and  having  the  same  double- 
looped  arrangement  that  prevails  in  the  preceding  layer:  they  are  com- 
paratively few  in  number,  and  are  placed  only  at  the  cardiac  orifice  and 
portion  of  the  stomach,  over  both  surfaces  of  which  they  are  spread,  some 
passing  obliquely  from  left  to  right,  others  from  right  to  left,  around  the 
cardiac  orifice,  to  which,  by  their  interlacing,  they  form  a  kind  of 
sphincter,  continuous  with  that  around  the  lower  end  of  the  oesophagus. 
Tlie  muscular  fibres  of  the  stomach  and  of  the  intestinal  canal  are  unstri- 
afed,  being  composed  of  elongated,  spindle-shaped  fibre -cells. 

(3)  and  (4)  The  mucous  memhrane  of  the  stomach,  which  rests  upon  a 
layer  of  loose  cellular  membrane,  or  suhnucous  tissue,  is  smooth,  level, 
soft,  and  velvety;  of  a  pale  pink  color  during  life,  and  in  the  contracted 
state  thrown  into  numerous,  chiefly  longitudinal,  folds  or  rugae,  which 
disappear  when  the  organ  is  distended. 

The  basis  of  the  mucous  membrane  is  a  fine  connective  tissue^  which 
approaches  closely  in  structure  to  adenoid  tissue;  this  tissue  Fupports  the 
Vol.  I.— 10. 


242 


HAND-BOOK  OF  PHYSIOLOGY. 


tubiilar  glands  of  which  the  superficial  and  chief  part  of  the  mucous 
membrane  is  composed,  and  passing  up  between  them  assists  in  binding 
them  together.  Here  and  there  are  to  be  found  in  this  coat,  immediately 
underneath  the  glands,  masses  of  adenoid  tissue  sufficiently  marked  to 
be  termed  by  some  lymphoid  follicles.  The  glands  are  separated  from 
the  rest  of  the  mucous  membrane  by  a  very  fi.ne  homogeneous  basement 
membrane. 

At  the  deepest  part  of  the  mucous  membrane  are  two  layers  (circular  and 
longitudinal)  of  unstriped  muscular  fibres,  called  the  muscularis  mucosce. 
which  separate  the  mucous  membrane  from  the  scanty  submucous  tissue. 

When  examined  with  a  lens,  the  internal  or  free  surface  of  the  stomach 
presents  a  peculiar  honeycomb  appearance,  produced  by  shallow  polygo- 
nal depressions,  the  diameter  of  which  varies  generally  from  -g-^-g-  tli  to 
-g^th  of  an  inch;  but  near  the  pylorus  is  as  much  as  y^th  of  an  inch. 
They  are  separated  by  slightly  elevated  ridges,  which  sometimes,  especially 
in  certain  morbid  states  of  the  stomach,  bear  minute,  narrow  vascular 
processes,  which  look  like  villi,  and  have  given  rise  to  the  erroneous  sup- 
position that  the  stomach  has  absorbing  villi,  like  those  of  the  small  in- 
testines. In  the  bottom  of  these  little  pits,  and  to  some  extent  between 
them,  minute  openings  are  visible,  which  are  the  orifices  of  the  ducts  of 
perpendicularly  arranged  tubular  glands  (Fig,  ITT),  imbedded  side  by 
side  in  sets  or  bundles,  on  the  surface  of  the  mucous  membrane,  and 
composing  nearly  the  whole  structure. 

Gastric  Glands. — Of  these  there  are  two  varieties,  {a)  Peptic,  {l) 
Pyloric  or  Mucous. 

{a)  Peptic  glands  are  found  throughout  the  whole  of  the  stomach  except 
at  the  pylorus.  They  are  arranged  in  groups  of  four  or  five,  which  are 
separated  by  a  fine  connective  tissue.  Two  or  three  tubes  often  open  into 
one  duct,  which  forms  about  a  third  of  the  whole  length  of  the  tube  and 
opens  on  the  surface.  The  ducts  are  lined  with  columnar  epithelium. 
Of  the  gland  tube  proper,  Z.^.,  the  part  of  the  gland  below  the  duct,  the 
upper  third  is  the  necl:  and  the  rest  the  hody.  The  neck  is  narrower 
than  the  body,  and  is  lined  with  granular  cubical  cells  which  are  continu- 
ous with  the  columnar  cells  of  the  duct.  Between  these  cells  and  the 
membrana  propria  of  the  tubes,  are  large  oval  or  spherical  cells,  opaque 
or  granular  in  appearance,  with  clear  oval  nuclei,  bulging  out  the  mem- 
brana propria;  these  cells  are  called  or  parietal  cells.  They  do  not 
form  a  continuous  layer.  The  body,  which  is  broader  than  the  neck  and 
terminates  in  a  blind  extremity  or  fundus  near  the  muscularis  mucosa?, 
is  lined  by  cells  continuous  with  the  cubical  or  central  '\41s  of  the  neck, 
but  longer,  more  columnar  and  more  transparent.  In  this  }nirt  are  a  few 
l)arietal  cells  of  tlie  same  kind  as  in  the  neck  (Pig.  ITT). 

As  tlie  i)yloru8  is  approaclied  tlie  gland  ducts  beconu^  longer,  and  the 
tube  pr(>])er  l)ecomes  shorter,  and  occasionally  branclied  at  the  fundus. 


DIGESTION. 


243 


(b)  Pyloric  Glands.— These  glands  (Fig.  179)  have  much  longer  ducts 
than  the  peptic  glands.  Into  each  duct  two  or  three  tubes  open  by  very 
short  and  narrow  necks,  and  the  body  of  each  tube  is  branched,  wavy, 
and  convoluted.  The  lumen  is  very  large.  The  ducts  are  lined  with 
columnar  epithelium,  and  the  neck  and  body  with  shorter  and  more  gran- 


FiG.  177.— From  a  vertical  section  through  the  mucous  membrane  of  the  cardiac  end  of  stomach. 
Two  peptic  glands  are  shown  with  a  duct  common  to  both,  one  gland  only  in  part,  a,  duct  with  col- 
immar  epithelium  becoming  shorter  as  the  cells  are  traced  downward;  n,  neck  of  gland  tubes,  with 
central  and  parietal  or  so-called  peptic  ceUs;  6,  fundus  with  curved  cwecal  extremity— the  parietal  ceUs 
are  not  so  numerous  here,    x  400.    (Klein  and  Noble  Smith.) 

Fig.  178.— Transverse  section  through  lower  part  of  peptic  glands  of  a  cat.  a,  peptic  cells;  b, 
smaU  spheroidal  or  cubical  cells;  c,  transverse  section  of  capillaries.  (Frey.) 

Fig.  179.— Section  showing  the  pyloric  glands,  s,  free  surface ;  d,  ducts  of  pyloric  glands ;  n,  neck 
of  same;  m,  the  gland  alveoU;  m  m,  muscularis  mucosae.   (Klein  and  Noble  Smith.) 


ular  cubical  cells,  which  correspond  with  the  central  cells  of  the  peptic 
glands.  During  secretion  the  cells  become,  as  in  the  case  of  the  peptic 
glands,  larger  and  the  granules  restricted  to  the  inner  zone  of  the  cell. 
As  they  approach  the  duodenum  the  pyloric  glands  become  larger,  more 


244  HAND-BOOK  OF  PHYSIOLOGY. 

convoluted  and  more  deeply  situated.  They  are  directly  continuous  with 
Brunner's  glands  in  the  duodenum.  (Watney.) 

Changes  in  the  gland  cells  during  secretion. — The  chief  or  cubical  cells 
of  the  peptic  glands^  and  the  corresponding  cells  of  the  pyloric  glands 
during  the  early  stage  of  digestion,  if  hardened  in  alcohol,  appear  swollen 
and  granular,  and  stain  readily.  At  a  later  stage  the  cells  become 
smaller,  but  more  granular  and  stain  even  more  readily.  The  parietal 
cells  swell  up,  but  are  otherwise  not  altered  during  digestion.  The  gran- 
ules, however,  in  the  alcohol-hardened  specimen,  are  believed  not  to  exist 
in  the  living  cells,  but  to  have  been  precipitated  by  the  hardening  re- 
agent; for  if  examined  during  life  they  appear  to  be  confined  to  the  inner 
zone  of  the  cells,  and  the  outer  zone  is  free  from  granules,  whereas  during 
rest  the  cell  is  granular  throughout.    These  granules  are  thought  to  be 


Fig.  180.— Plan  of  the  blood-vessels  of  the  stomach,  as  they  would  be  seen  in  a  vertical  section, 
a,  arteries,  passing  up  from  the  vessels  of  submucous  coat;  b,  capillaries  branching  between  and 
around  the  tubes;  c,  superficial  plexus  of  capillaries  occup3-ing  the  ridges  of  the  mucous  membrane; 
d,  vein  formed  by  the  union  of  veins  which,  having  collected  the  blood  of  the  superficial  capillary 
plexus,  are  seen  passing  down  between  the  tubes.  (Brinton.) 

pepsin,  or  the  substance  from  which  pepsin  is  formed,  pepsinogen,  which 
is  during  rest  stored  chiefly  in  the  inner  zone  of  the  cells  and  discharged 
into  the  lumen  of  the  tube  during  secretion.  (Langley.) 

Lymphatics. — Lymphatic  vessels  surround  the  gland  tubes  to  a  greater 
or  less  extent.  Toward  the  fundus  of  the  peptic  glands  are  found  masses 
of  lymphoid  tissue,  which  may  appear  as  distinct  follicles,  somewhat  like 
the  solitary  glands  of  the  small  intestine. 

Blood-vessels. — Tlie  blood-vessels  of  the  stomach,  which  first  break  up 
in  the  submucous  tissue,  send  branches  upward  between  the  closely 
packed  glandular  tubes,  anastomosing  around  them  by  means  of  a  fine 
capillary  network,  with  oblong  meshes.  Continuous  with  this  deeper 
plexus,  or  prolonged  u])ward  from  it,  so  to  s})eak,  is  a  more  superficial 
network  of  larger  cai)illaries,  which  branch  densely  around  the  orifices 


I 


DIGESTION. 


245 


of  the  tubes,  and  form  the  framework  on  which  are  moulded  the  small 
elevated  ridges  of  mucous  membrane  bounding  the  minute,  polygonal 
pits  before  referred  to.  From  this  superficial  network  the  veins  chiefly 
take  their  origin.  Thence  passing  down  between  the  tubes,  with  no  very 
free  connection  with  the  deeper  inter-tuhular  capillary  plexus,  they  open 
finally  into  the  venous  network  in  the  submucous  tissue. 

Nerves. — The  nerves  of  the  stomach  are  derived  from  the  pneumo- 
gastric  and  sympathetic,  and  form  a  plexus  in  the  submucous  and  mus- 
cular coats,  containing  many  ganglia  (Remak,  Meissner). 

Digestion"  iit  the  Stomach. 

Gastric  Juice. — The  functions  of  the  stomach  are  to  secrete  a  diges- 
tive fluid  (gastric  juice),  to  the  action  of  which  the  food  is  next  subjected 
after  it  has  entered  the  cavity  of  the  stomach  from  the  oesophagus;  to 
thoroughly  incorporate  the  fluid  with  the  food  by  means  of  its  muscular 
movements;  and  to  absorb  such  substances  as  are  capable  of  absorption. 
AVhile  the  stomach  contains  no  food,  and  is  inactive,  no  gastric  fluid  is 
secreted;  and  mucus,  which  is  either  neutral  or  slightly  alkaline,  covers 
its  surface.  But  immediately  on  the  introduction  of  food  or  other  sub- 
stance the  mucous  membrane,  previously  quite  pale,  becomes  slightly 
turgid  and  reddened  with  the  influx  of  a  larger  quantity  of  blood;  the 
gastric  glands  commence  secreting  actively,  and  an  acid  fluid  is  poured 
out  in  minute  drops,  which  gradually  run  together  and  flow  down  the 
walls  of  the  stomach,  or  soak  into  the  substances  within  it. 

Chemical  Composition  of  Gastric  Juice. — The  first  accurate 
analysis  of  gastric  juice  was  made  by  Prout:  but  it  does  not  appear  to 
have  been  collected  in  any  large  quantity,  or  pure  and  separate  from  food, 
until  the  time  when  Beaumont  was  enabled,  by  a  fortunate  circumstance, 
to  obtain  it  from  the  stomach  of  a  man  named  St.  Martin,  in  whom  there 
existed,  as  the  result  of  a  gunshot  wound,  an  opening  leading  directly 
into  the  stomach,  near  the  upper  extremity  of  the  great  curvature,  and 
three  inches  from  the  cardiac  orifice.  The  introduction  of  any  m.echanical 
irritant,  such  as  the  bulb  of  a  thermometer,  into  the  stomach,  excited  at 
once  the  secretion  of  gastric  fluid.  This  was  drawn  off,  and  was  often 
obtained  to  the  extent  of  nearly  an  ounce.  The  introduction  of  aliment- 
ary substances  caused  a  much  more  rapid  and  abundant  secretion  than 
did  other  mechanical  irritants.  Ko  increase  of  temperature  could  be 
detected  during  the  most  active  secretion;  the  thermometer  introducjed 
into  the  stomach  always  stood  at  100°  F.  (37*8°  C.)  except  during  muscu- 
lar exertion,  when  the  temperature  of  the  stomach,  like  that  of  other 
parts  of  the  body,  rose  one  or  two  degrees  higher. 

The  chemical  composition  of  human  gastric  juice  has  been  also  in- 
vestigated by  Schmidt.    The  fluid  in  this  case  was  obtained  by  means  of  an 


246 


HAND-BOOK  OF  PHYSIOLOGY. 


accidental  gastric  fistula,  which  existed  for  several  years  below  the  left 
manimar}^  region  of  a  patient  between  the  cartilages  of  the  ninth  and 
tenth  ribs.  The  mucous  membrane  was  excited  to  action  b}^  the  introduc- 
tion of  some  hard  matter,  such  as  dry  peas,  and  the  secretion  was  removed 
by  means  of  an  elastic  tube.  The  fluid  thus  obtained  was  found  to  be  acid, 
limpid,  odorless,  with  a  mawkish  taste — with  a  specific  gravity  of  1002, 
or  a  little  more.  It  contained  a  few  cells,  seen  with  the  microscope,  and 
some  fine  granular  matter.  The  analysis  of  the  fluid  obtained  in  this  is 
given  below.  The  gastric  juice  of  dogs  and  other  animals  obtained  by 
the  introduction  into  the  stomach  of  a  clean  sponge  through  an  artifi- 
cially made  gastric  fistula,  shows  a  decided  difference  in  composition,  but 
possibly  this  is  due,  at  least  in  part,  to  admixture  with  food. 


Chemical  CoMPOsmoi^"  of  Gastkic  Juice. 

Dogs.  Human. 

Water                                                           971-17  994*4 

Solids                                                             28-82  5-39 

Solids- 
Ferment— Pepsin        .       .       .       .  17*5  3-19 
Hydrochloric  acid  (free^       ....     2-7  -2 

Salts- 
Calcium,  sodium,  and  potassium,  chlorides;  and 
calcium,  magnesium,  and  iron,  phosphates    .    8*57  2*19 

The  quantity  of  gastric  juice  secreted  daily  has  been  variously  esti- 
mated; but  the  average  for  a  healthy  adult  may  be  assumed  to  range  from 
ten  to  twenty  pints  in  the  twenty-four  hours.  The  acidity  of  the  fluid  is 
due  to  free  liydrocliloric  acid,  although  other  acids,  e.g.,  lactic,  acetic, 
butyric,  are  not  unfrequently  to  be  found  therein  as  products  of  gastric 
digestion.  The  amount  of  hydrochloric  acid  varies  from  2  to  -2  per  1000 
parts.  In  healthy  gastric  juice  the  amount  of  free  acid  may  be  as  much 
as  -2  per  cent. 

As  regards  the  formation  of  pepsin  and  acid,  the  former  is  produced 
by  the  central  or  chief  cells  of  the  peptic  glands,  and  also  most  likely  by 
the  similar  cells  in  the  pyloric  glands;  the  acid  is  chiefly  found  at  the 
surface  of  the  mucous  membrane,  but  is  in  all  probability  formed  by  the 
secreting  action  of  the  parietal  cells  of  the  peptic  glands,  as  no  acid  is 
formed  by  the  pyloric  glands  in  wliich  this  variety  of  cell  is  absent. 

The  ferment  Pepsin  (p.  24())  can  be  procured  by  digesting  portions 
of  the  mucous  membrane  of  tlu^  stomacli  in  cold  water,  after  they  liave 
been  macerated  for  some  time  in  water  at  a  temperature  80° — lOO*-"*  F. 
(27-0 — 37 '8°  C).  The  warm  water  dissolves  various  substances  as  well 
as  some  of  the  pepsin,  but  the  cold  water  takes  up  little  else  than  pepsin, 
which  is  contained  in  a  greyish-brown  viscid  fluid,  on  eva])orating  the 


DIGESTION. 


cold  solution.  The  addition  of  alcohol  throws  down  the  pepsin  in  greyish- 
white  flocculi.  Glycerine  also  has  the  property  of  dissolving  out  the  fer- 
ment; and  if  the  mucous  membrane  be  finely  minced  and  the  moisture 
removed  by  absolute  alcohol,  a  powerful  extract  may  be  obtained  by 
throwing  into  glycerine. 

Functions. — The  digestive  power  of  the  gastric  juice  depends  on  the 
pepsin  and  acid  contained  in  it,  both  of  which  are,  under  ordinary  cir- 
cumstances, necessary  for  the  process. 

The  general  effect  of  digestion  in  the  stomach,  is  the  conversion  of 
the  food  into  cliyme,  a  substance  of  various  composition  according  to  the 
nature  of  the  food,  yet  always  presenting  a  characteristic  thick,  pultace- 
ous,  grumous  consistence,  with  the  undigested  portions  of  the  food  mixed 
in  a  more  fluid  substance,  and  a  strong,  disagreeable  acid  odor  and  taste. 

The  chief  function  of  the  gastric  juice  is  to  convert  ])Toteids  into  pep- 
tones. This  action  may  be  shown  by  adding  a  little  gastric  juice  (natural 
or  artificial)  to  some  diluted  egg-albumin,  and  keeping  the  mixture  at  a 
temperature  of  about  100°  F.  (37 '8°  C);  it  is  soon  found  that  the  albu- 
min cannot  be  precipitated  on  boiling,  but  that  if  the  solution  be  neutral- 
ized with  an  alkali,  a  precipitate  of  acid- albumin  is  thrown  down.  After 
a  while  the  proportion  of  acid-albumin  gradually  diminishes,  so  that  at 
last  scarcely  any  precipitate  results  on  neutralization,  and  finally  it  is 
found  that  all  the  albumin  has  been  changed  into  another  proteid  sub- 
stance which  is  not  precipitated  on  boiling  or  on  neutralization.  This  is 
called  peptone. 

Characteristics  of  Peptones. — Peptones  have  certain  characteristics 
which  distinguish  them  from  other  proteids.  1.  They  are  diffusihUj  i.e., 
they  possess  the  property  of  passing  through  animal  membranes.  2. 
They  cannot  be  precipitated  by  heat,  nitric,  or  acetic  acid,  or  potassium 
ferrocyanide  and  acetic  acid.  They  are,  however,  thrown  down  by  tannic 
acid,  by  mercuric  chloride  and  by  picric  acid.  3.  They  are  very  soluble 
in  water  and  in  neutral  saline  solutions. 

In  their  ditfusibility  peptones  differ  remarkably  from  egg-albumin, 
and  on  this  diffusibility  depends  one  of  their  chief  uses.  Egg-albumin  as 
such,  even  in  a  state  of  solution,  would  be  of  little  service  as  food,  inas- 
much as  its  indiffusibility  w^ould  effectually  prevent  its  passing  by  absorp- 
tion into  the  blood-vessels  of  the  stomach  and  intestinal  canal.  Changed, 
however,  by  the  action  of  the  gastric  juice  into  peptones,  albuminous 
matters  diffuse  readily,  and  are  thus  quickly  absorbed. 

After  entering  the  blood  the  peptones  are  very  soon  again  modified, 
so  as  to  re-assume  the  chemical  characters  of  albumin,  a  change  as  neces- 
sary for  preventing  their  diffusing  out  of  the  blood-vessels,  as  the  previous 
change  was  for  enabling  them  to  pass  in.  This  is  effected,  probably,  in 
great  part  by  the  agency  of  the  liver. 

Products  of  Gastric  Digestion. — The  chief  product  of  gastric 


248 


HAND-BOOK  OF  PHYSIOLOGY. 


t. 


digestion  is  undoubtedly  peptone.  We  have  seen^  however,  in  the  above 
experiment  that  there  is  a  by-product,  and  this  is  almost  identical  with 
syntonin  or  acid  albumin.  This  body  is  probably  not  exactly  identical, 
however,  with  syntonin,  and  its  old  name  of  parajjeptone  had  better  be 
retained.  The  conversion  of  native  albumin  into  acid  albumin  may  be 
effected  by  the  hydrochloric  acid  alone,  but  the  further  action  is  undoubt- 
edly due  to  the  ferment  and  the  acid  together,  as  although  under  high 
pressure  any  acid  solution  may,  it  is  said,  if  strong  enough,  produce  the 
entire  conversion  into  peptone,  under  the  condition  of  digestion  in  the 
stomach  this  would  be  quite  impossible;  and,  on  the  other  hand,  pepsin 
will  not  act  without  the  presence  of  acid.  The  production  of  two  forms 
of  peptone  is  usually  recognized,  called  respectively  anti-^e.^ionQ  and 
Aem^-peptone.  Their  differences  in  chemical  properties  have  not  yet  been 
made  out,  but  they  are  distinguished  by  this  remarkable  fact,  that  the 
pancreatic  juice,  while  possessing  no  action  over  the  former,  is  able  to 
convert  the  latter  into  leucin  and  ty rosin.  Pepsin  acts  the  part  of  a 
hydrolytic  ferment  (proteolytic),  and  appears  to  cause  hydration  of  albu- 
min, peptone  being  a  highly  hydrated  form  of  albumin. 

Circumstances  favoring  Gastric  Digestion. — 1.  A  temperature 
of  about  100°  F.  (37 '8°  C);  at  32°  F.  (0°  0.)  it  is  delayed,  and  by  boil- 
ing is  altogether  stopped.  2.  An  acid  medium  is  necessary.  Hydro- 
chloric is  the  best  acid  for  the  purpose.  Excess  of  acid  or  neutralization 
stops  the  process.  3.  The  removal  of  the  products  of  digestion.  Excess 
of  peptone  delays  the  action. 

Action  of  the  Gastric  Juice  on  Bodies  other  than  Proteids. 
— ^All  proteids  are  converted  by  the  gastric  juice  into  peptones,  and,  there- 
fore, whether  they  be  taken  into  the  body  in  meat,  eggs,  milk,  bread,  or 
other  foods,  the  resultant  still  is  peptone. 

Milh  is  curdled,  the  casein  being  precipitated,  and  then  dissolved. 
The  curdling  is  due  to  a  special  ferment  of  the  gastric  juice  (curdling 
ferment),  and  is  not  due  to  the  action  of  the  free  acid  only.  The  effect 
of  rennet,  which  is  a  decoction  of  the  fourth  stomach  of  a  calf  in  brine, 
has  long  been  known,  as  it  is  used  extensively  to  cause  precipitation  of 
casein  in  cheese  manufacture. 

The  ferment  which  produces  this  curdling  action  is  distinct  from 
pepsin. 

Gelatin  is  dissolved  and  changed  into  peptone,  as  are  also  cliondrin 
and  elastin;  but  tmiciu,  and  the  Jiorny  tissues,  keratin  generally  are  un- 
affected. 

On  the  amylaceotis  articles  of  food,  and  upon  pure  oleaginous  prin- 
ciples the  gastric  juice  has  no  action.  Tu  the  case  of  adipose  tissue,  its 
effo(;t  is  to  dissolve  the  aroohir  tissue,  {ilhiiniinous  cell-walls,  etc.,  wliich 
enter  into  its  comi)osition,  by  wliich  means  the  fat  is  able  to  mingle 
more  unifornily  with  the  other  constituents  of  the  chyme. 


DIGESTION. 


249 


The  gastric  fluid  acts  as  a  general  solvent  for  some  of  the  mime  con- 
stituents of  the  food,  as,  for  example,  particles  of  common  salt,  which 
may  happen  to  have  escaped  solution  in  the  saliva;  while  its  acid  may 
enable  it  to  dissolve  some  other  salts  which  are  insoluble  in  the  latter  or 
in  water*  It  also  dissolves  cane  sugar,  and  by  the  aid  of  its  mucus  causes 
its  conversion  in  part  into  grape  sugar. 

The  action  of  the  gastric  juice  in  preventing  and  checking  putrefac- 
tion has  been  often  directly  demonstrated.  Indeed,  that  the  secretions 
which  the  food  meets  with  in  the  alimentary  canal  are  antiseptic  in  their 
action,  is  what  might  be  anticipated,  not  only  from  the  proneness  to  de- 
composition of  organic  matters,  such  as  those  used  as  food,  especially 
under  the  influence  of  warmth  and  moisture,  but  also  from  the  well- 
known  fact  that  decomposing  flesh  (e.g.,  high  game)  may  be  eaten  with 
impunity,  while  it  would  certainly  cause  disease  were  it  allowed  to  enter 
the  blood  by  any  other  route  than  that  formed  by  the  organs  of  digestion. 

Time  occupied  in  Gastric  Digestion. — Under  ordinary  condi- 
tions, from  three  to  four  hours  may  be  taken  as  the  average  time  occupied 
by  the  digestion  of  a  meal  in  the  stomach.  But  many  circumstances  v/ill 
modify  the  rate  of  gastric  digestion.  The  chief  are:  the  nature  of  the 
food  taken  and  its  quantity  (the  stomach  should  be  fairly  filled — not  dis- 
tended); the  time  that  has  elapsed  since  the  last  meal,  which  should  be 
at  least  enough  for  the  stomach  to  be  quite  clear  of  food;  the  amount  of 
exercise  previous  and  subsequent  to  a  meal  (gentle  exercise  being  favor- 
able, over-exertion  injurious  to  digestion);  the  state  of  mind  (tranquillity 
of  temper  being  essential,  in  most  cases,  to  a  quick  and  due  digestion); 
the  bodily  health;  and  some  others. 

Movements  of  the  Stomach. — The  gastric  fluid  is  assisted  in 
accomplishing  its  share  in  digestion  by  the  movements  of  the  stomach. 
In  granivorous  birds,  for  example,  the  contraction  of  the  strong  muscular 
gizzard  affords  a  necessary  aid  to  digestion,  by  grinding  and  triturating 
the  hard  seeds  which  constitute  part  of  the  food.  But  in  the  stomachs  of 
man  and  other  Mammalia  the  motions  of  the  muscular  coat  are  too  feeble 
to  exercise  any  such  mechanical  force  on  the  food;  neither  are  they 
needed,  for  mastication  has  already  done  the  mechanical  work  of  a  giz- 
zard; and  experiments  have  demonstrated  that  substances  enclosed  in 
perforated  tubes,  and  consequently  protected  from  mechanical  .influence, 
are  yet  digested. 

The  normal  actions  of  the  muscular  fibres  of  the  human  stomach 
appear  to  have  a  threefold  purpose;  (1)  to  adapt  the  stomach  to  the 
quantity  of  food  in  it,  so  that  its  walls  may  be  in  contact  with  the  food 
on  all  sides,  and,  at  the  same  time,  may  exercise  a  certain  amount  of 
compression  upon  it;  (2)  to  keep  the  orifices  of  the- stomach  closed  until 
the  food  is  digested;  and  (3)  to  perform  certain  peristaltic  movements,  . 
Avhereby  the  food,  as  it  becomes  chymified,  is  gradually  propelled  toward. 


250 


HAND-BOOK  OF  PHYSIOLOGY. 


and  ultimately  through,  the  pylorus.  In  accomplishing  this  latter  end, 
the  movements  without  doubt  materially  contribute  toward  effecting  a 
thorough  intermingling  of  the  food  and  the  gastric  fluid. 

When  digestion  is  not  going  on,  the  stomach  is  uniformly  contracted, 
its  orifices  not  more  firmly  than  the  rest  of  its  walls;  but,  if  examined 
shortly  after  the  introduction  of  food,  it  is  found  closely  encircling  its 
contents,  and  its  orifices  are  firmly  closed  like  sphincters.  The  cardiac 
orifice,  every  time  food  is  swallowed,  opens  to  admit  its  passage  to  the 
stomach,  and  immediately  again  closes.  The  pyloric  orifice,  during  the 
first  part  of  gastric  digestion,  is  usually  so  completely  closed,  that  even 
when  the  stomach  is  separated  from  the  intestines,  none  of  its  contents 
escape.  But  toward  the  termination  of  the  digestive  process,  the  pylorus 
seems  to  offer  less  resistance  to  the  passage  of  substances  from  the 
stomach;  first  it  yields  to  allow  the  successively  digested  portions  to  go 
through  it;  and  then  it  allows  the  transit  of  even  undigested  substances. 
It  appears  that  food,  so  soon  as  it  enters  the  stomach,  is  subjected  to  a 
kind  of  peristaltic  action  oi  the  muscular  coat,  whereby  the  digested  por- 
tions are  gradually  moved  toward  the  pylorus.  The  movements  were 
observed  to  increase  in  rapidity  as  the  process  of  chymification  advanced, 
and  were  continued  until  it  was  completed. 

The  contraction  of  the  fibres  situated  toward  the  pyloric  end  of  the 
stomach  seems  to  be  more  energetic  and  more  decidedly  peristaltic  than 
those  of  the  cardiac  portion.  Thus,  it  was  found  in  the  case  of  St. 
Martin,  that  when  the  bulb  of  the  thermometer  was  placed  about  three 
inches  from  the  pylorus,  through  the  gastric  fistula,  it  was  tightly  em- 
braced from,  time  to  time,  and  drawn  toward  the  pyloric  orifice  for  a  dis- 
tance of  three  or  four  inches.  The  object  of  this  movement  appears  to 
be,  as  just  said,  to  carry  the  food  toward  the  pylorus  as  fast  as  it  is  formed 
into  chyme,  and  to  propel  the  chyme  into  the  duodenum;  the  undigested 
portions  of  food  being  kept  back  until  they  are  also  reduced  into  chyme, 
or  until  all  that  is  digestible  has  passed  out.  The  action  of  these  fibres 
is  often  seen  in  the  contracted  state  of  the  pyloric  portion  of  the  stomach 
after  death,  when  it  alone  is  contracted  and  firm,  while  the  cardiac  por- 
tion forms  a  dilated  sac.  Sometimes,  by  a  predominant  action  of  strong 
circular  fibres  placed  between  tlie  cardia  and  pjdorus,  the  two  portions, 
or  ends  ag  they  are  called,  of  the  stomach,  are  partially  separated  from 
each  other  by  a  kind  of  hour-glass  contraction.  By  means  of  the  peri- 
staltic action  of  tlie  muscular  coats  of  the  stonuxcli,  not  merely  is  chymitied 
food  gradually  propelled  through  the  pylorus,  but  a  kind  of  double  cur- 
rent is  continually  kept  up  among  the  contents  of  the  stomach,  the  cir- 
cumferential parts  of  the  mass  being  gradually  moved  ouAvard  toward  the 
pylorus  by  the  contraction  of  the  muscular  libres,  while  the  central  por- 
tions are  propelled  in  the  opposite  direction,  namely,  toward  the  cardiac 
orifice;  in  this  way  is  kept  up  a  constant  circulation  of  the  contents  of 


DIGESTION. 


251 


the  viscus,  highly  conducive  to  their  free  mixture  with  the  gastric  fluid 
{ind  to  their  ready  digestion. 

Vomiting. — The  expulsion  of  the  contents  of  the  stomach  in  vomit- 
ing, like  that  of  mucous  or  other  matter  from  the  lungs  in  coughing,  is 
preceded  by  an  inspiration;  the  glottis  is  then  closed,  and  immediately 
afterward  the  abdominal  muscles  strongly  act;  but  here  occurs  the  dif- 
ference in  the  two  actions.  Instead  of  the  vocal  cords  yielding  to  the 
action  of  the  abdominal  muscles,  they  remain  tightly  closed.  Thus  the 
diaphragm  being  unable  to  go  up,  forms  an  unyielding  surface  against 
which  the  stomach  can  be  pressed.  In  this  way,  as  well  as  by  its  own 
contraction,  it  infixed,  to  use  a  technical  phrase.  At  the  same  time  the 
cardiac  sphincter-muscle  being  relaxed,  and  the  orifice  which  it  naturally 
guards  being  actively  dilated,  while  the  pylorus  is  closed,  and  the  stomach 
itself  also  contracting,  the  action  of  the  abdominal  muscles,  by  these 
means  assisted,  expels  the  contents  of  the  organ  through  the  oesophagus, 
pharynx,  and  mouth.  The  reversed  peristaltic  action  of  the  oesophagus 
probably  increases  the  effect. 

It  has  been  frequently  stated  that  the  stomach  itself  is  quite  passive 
during  vomiting,  and  that  the  expulsion  of  its  contents  is  effected  solely 
by  the  pressure  exerted  upon  it  when  the  capacity  of.  the  abdomen  is 
diminished  by  the  contraction  of  the  diaphragm,  and  subsequently  of  the 
abdominal  muscles.  The  experiments  and  observations,  however,  which 
are  supposed  to  confirm  this  statement,  only  show  that  the  contraction  of 
the  abdominal  muscles  alone  is  sufficient  to  expel  matters  from  an  unre- 
sisting bag  through  the  'oesophagus;  and  that,  under  very  abnormal 
circumstances,  the  stomach,  by  itself,  cannot  expel  its  contents.  They  by 
no  means  show  that  in  ordinary  vomiting  the  stomach  is  passive;  and, 
on  the  other  hand,  there  are  good  reasons  for  believing  the  contrary. 

It  is  true  that  facts  are  wanting  to  demonstrate  with  certainty  this 
action  of  the  stomach  in  vomiting;  but  some  of  the  cases  of  fistulous  open- 
ing into  the  organ  appear  to  support  the  belief  that  it  does  take  place; 
and  the  analogy  of  the  case  of  the  stomach  with  that  of  the  other  hollow 
viscera,  as  the  rectum  and  bladder,  may  be  also  cited  in  confirmation. 

The  muscles  concerned  in  the  act  of  vomiting,  are  chiefly  and  pri- 
marily those  of  the  abdomen;  the  diaphragm  also  acts,  but  usually  not  as 
the  muscles  of  the  abdominal  walls  do.  They  contract  and  compress  the 
stomach  more  and  more  toward  the  diaphragm;  and  the  diaphragm 
(which  is  usually  drawn  down  in  the  deep  inspiration  that  precedes  each 
act  of  vomiting)  is  fixed,  and  presents  an  unyielding  surface  against 
which  the  stomach  may  be  pressed.  The  diaphragm  is,  therefore,  as  a 
rule,  passive  during  the  actual  expulsion  of  the  contents  of  the  stomach. 
But  there  are  grounds  for  believing  that  sometimes  this  muscle 
actively  contracts,  so  that  the  stomach  is,  so  to  speak,  squeezed  between 
the  descending  diaphragm  and  the  retracting  abdominal  walls. 


252 


HAND-BOOK  OF  PHYSIOLOGY. 


Some  persons  possess  the  power  of  vomiting  at  will,  without  applying 
any  undue  irritation  to  the  stomach,  but  simply  by  a  voluntary  effort. 
It  seems  also,  that  this  power  may  be  acquired  by  those  who  do  not 
naturally  possess  it,  and  by  continual  practice  may  become  a  habit.  There 
are  cases  also  of  rare  occurrence  in  which  persons  habitually  swallow  their 
food  hastily,  and  nearly  unmasticated,  and  then  at  their  leisure  regurgi- 
tate it,  piece  by  piece,  into  their  mouth,  remasticate,  and  again  swallow 
it,  like  members  of  the  ruminant  order  of  Mammalia. 

The  various  nerve- act  ions  concerned  in  vomiting  are  governed  by  a 
nerve-centre  situate  in  the  medulla  oblongata. 

The  sensory  nerves  are  the  fifth,  glosso-pharyngeal  and  vagus  princi- 
pally; but,  as  well,  vomiting  may  occur  from  stimulation  of  sensory 
nerves  from  many  organs,  e.g.,  kidney,  testicle,  etc.  The  centre  may  also 
be  stimulated  by  impressions  from  the  cerebrum  and  cerebellum,  so  called 
central  vomiting  occurring  in  disease  of  those  parts.  The  efferent  im- 
pulses are  carried  by  the  phrenics  and  the  spinal  nerves. 

Influence  of  the  Nervous  System  on  Gastric  Digestion. — Th( 
normal  movements  of  the  stomach  during  gastric  digestion  are  directlj 
connected  with  the  plexus  of  nerves  and  ganglia  contained  in  its  walls, 
the  presence  of  food  acting  as  a  stimulus  which  is  conveyed  to  the  gan- 
glia and  reflected  to  the  muscular  fibres.  The  stomach  is,  however,  also 
directly  connected  with  the  higher  nerve-centres  by  means  of  branches 
of  the  vagus  and  solar  plexus  of  the  sympathetic.  The  vaso-motor  fibres 
of  the  latter  are  derived,  probably,  from  tlie  splanchnic  nerves. 

The  exact  function  of  the  vagi  in  connection  with  the  movements  of 
the  stomach  is  not  certainly  known.  Irritation  of  the  vagi  produces  co]i- 
traction  of  the  stomach,  if  digestion  is  proceeding;  while,  on  the  other 
hand,  peristaltic  action  is  retarded  or  stopped,  when  these  nerves  are 
divided. 

Bernard,  watching  the  act  of  gastric  digestion  in  dogs  which  had  fis- 
tulous openings  into  their  stomachs,  saw  that  on  the  instant  of  dividing 
their  vagic  nerves,  the  process  of  digestion  was  stopped,  and  the  mucous 
membrane  of  the  stomach,  previously  turgid  with  blood,  became  pale, 
and  ceased  to  secrete.  These  facts  may  be  explained  by  the  theory  that 
the  vagi  are  the  media  by  which,  during  digestion,  an  inliiliforg  impulse 
is  conducted  to  the  vaso-motor  centre  in  the  medulla;  such  impulse  being 
reflected  along  the  splanchnic  nerves  to  the  blood-vessels  of  the  stomach, 
and  causing  their  dilatation  ( Rutherford).  From  other  experiments  it  ma^ 
be  gathered,  that  although  division  of  both  vagi  always  temporarily  sus- 
pends the  secretion  of  gastric  fluid,  and  so  arrests  the  process  of  digestion, 
being  occasionally  followed  by  death  from  inanition;  yet  the  digestive 
power5  of  the  stomach  may  be  completely  restored  after  the  operation, 
jind  the  formation  of  chyme  and  the  nutrition  of  the  animal  may  be 
can-iod  on  almost  as  perfectly  as  in  health.    This  Avould  indicate  the 


DIGESTION. 


253 


existence  of  a  special  local  nervous  mechanism  which  controls  the 
secretion. 

Bernard  found  that  galvanic  stimulus  of  these  nerves  excited  an  active 
secretion  of  the  fluid,  while  a  like  stimulus  applied  to  the  sympathetic 
nerves  issuing  from  the  semilunar  ganglia,  caused  a  diminution  and  even 
complete  arrest  of  the  secretion. 

The  influence  of  the  higher  nerve-centres  on  gastric  digestion,  as  in 
the  case  of  mental  emotion,  is  too  well  known  to  need  more  than  a  ref- 
erence. 

Digestion  of  the  Stomach  after  Death. — If  an  animal  die  dur- 
ing the  process  of  gastric  digestion,  and  when,  therefore,  a  quantity  of 
gastric  juice  is  present  in  the  interior  of  the  stomach,  the  walls  of  this 
organ  itself  are  frequently  themselves  acted  on  by  their  own  secretion, 
and  to  such  an  extent,  that  a  perforation  of  considerable  size  may  be  pro- 
duced, and  the  contents  of  the  stomach  may  in  part  escape  into  the 
cavity  of  the  abdomen.  This  phenomenon  is  not  unfreqiiently  observed 
in  post-mortem  examinations  of  the  human  body.  If  a  rabbit  be  killed 
during  a  period  of  digestion,  and  afterward  exposed  to  artificial  warmth 
to  prevent  its  temperature  from  falling,  not  only  the  stomach,  but  many 
of  the  surrounding  parts,  will  be  found  to  have  been  dissolved  (Pavy). 

From  these  facts,  it  becomes  an  interesting  question  why,  during  life, 
the  stomach  is  free  from  liability  to  injury  from  a  secretion  which,  after 
death,  is  capable  of  such  destructive  effects? 

It  is  only  necessary  to  refer  to  the  idea  of  Bernard,  that  the  living 
stomach  finds  protection  from  its  secretion  in  the  presence  of  epithelium 
and  mucus,  which  are  constantly  renewed  in  the  same  degree  that  they 
are  constantly  dissolved,  in  order  to  remark  that,  although  the  gastric 
mucus  is  probably  protective,  this  theory,  so  far  as  the  epithelium  is  con- 
cerned, has  been  disproved  by  experiments  of  Pavy\  in  which  the  mucous 
membrane  of  the  stomachs  of  dogs  was  dissected  off  for  a  small  space, 
and,  on  killing  the  animals  some  days  afterward,  no  sign  of  digestion  of 
the  stomach  was  visible.  ''Upon  one  occasion,  after  removing  the  mu- 
cous membrane,  and  exposing  the  muscular  fibres  over  a  space  of  about  an 
inch  and  a  half  in  diameter,  the  animal  was  allowed  to  live  for  ten  days. 
It  ate  food  every  day,  and  seemed  scarcely  affected  by  the  operation.  Life 
was  destroyed  whilst  digestion  was  being  carried  on,  and  the  lesion  in  the 
stomach  was  found  very  nearly  repaired:  new  matter  had  been  deposited 
in  the  place  of  what  had  been  removed,  and  the  denuded  spot  had  con- 
tracted to  much  less  than  its  original  dimensions. 

Pavy  believes  that  the  natural  alkalinity  of  the  blood,  which  circulates 
so  freely  during  life  in  the  walls  of  the  stomach,  is  sufficient  to  neutralize 
the  acidity  of  the  gastric  juice;  and  as  may  be  gathered  from  what  has 
been  previously  said,  the  neutralization  of  the  acidity  of  the  gastric  secre- 
tion is  quite  sufficient  to  destroy  its  digestive  powers;  but  the  experi- 


254  HAND-BOOK  OF  PHYSIOLOGY. 

ments  adduced  in  favor  of  this  theory  are  open  to  many  objections,  and 
afford  only  a  negative  support  to  the  conclusions  they  are  intended  to 
prove.    Again,  the  pancreatic  secretion  acts  best  on  proteids  in  an  alka.' 


Fig.  181.— Auerbach's  nerve-plexus  in  small  intestine.  The  plexus  consists  of  flbrillated  substance, 
and  is  made  up  of  trabeculae  of  various  thicknesses.  Nucleus-like  elements  and  gangUon-cells  are  im- 
bedded in  the  plexus,  the  whole  of  which  is  enclosed  in  a  nucleated  sheath.  (Kllein.) 

line  medium;  but  it  has  no  digestive  action  on  the  living  intestine.  It 
must  be  confessed  that  no  entirely  satisfactory  theory  has  been  yet  stated. 

The  Iktestines. 

The  Intestinal  Canal  is  divided  into  two  chief  portions,  named  from 
their  differences  in  diameter,  the  (I.)  small  and  (II.)  large  intestine  (Fig. 
165).  These  are  continuous  with  each  other,  and  communicate  by  means 
of  an  opening  guarded  by  a  valve,  the  ileo-ccecal  valve,  vrhich  allows  the 
passage  of  the  products  of  digestion  from  the  small  into  the  large  bowel, 
but  not,  under  ordinary  circumstances,  in  the  opposite  direction. 

/.  Tlie  Small  Intestine. — The  Small  Intestine,  the  average  length  of 
which  in  an  adult  is  about  twenty  feet,  has  been  divided,  for  convenience 
of  description,  into  three  portions,  viz.,  the  duodenum,  which  extends  for 
eight  or  ten  inches  beyond  the  pylorus;  the  jejunum,  which  forms  two- 
fifths,  and  the  ileum,  which  forms  three-fifths  of  the  rest  of  the  canal. 

Structure. — The  small  intestine,  like  the  stomach,  is  constructed  of 
four  principal  coats,  viz. ,  the  serous,  muscular,  submucous,  and  mucous. 

(1)  The  sei'ous  coat,  formed  by  the  visceral  layer  of  the  peritoneum, 
and  has  the  structure  of  serous  membranes  in  general. 

{%)  The  muscular-  coats  consist  of  an  internal  circular  and  an  external 
longitudinal  layei*:  the  former  is  usually  considerably  the  thicker.  Both 


DIGESTION. 


255 


alike  consist  of  bundles  of  unstriped  muscular  tissue  supported  by  con- 
nective tissue.  They  are  well  provided  with  lymphatic  vessels,  which 
form  a  set  distinct  from- those  of  the  mucous  membrane. 

Between  the  two  muscular  coats  is  a  nerve-plexus  (Auerbach^s  plexus, 
plexos  myentericus)  (Pig.  181)  similar  in  structure  to  Meissner's  (in  the 
submucous  tissue),  but  with  more  numerous  ganglia.  This  plexus  regu- 
lates the  peristaltic  movements  of  the  muscular  coats  of  the  intestines. 

(3)  Between  the  mucous  and  muscular  coats,  is  the  submucous  coat, 
which  consists  of  connective  tissue,  in  which  numerous  blood-vessels  and 
lymphatics  ramify.  A  fine  plexus,  consisting  mainly  of  non-medullated 
nerve-fibres,  "Meissner's  plexus,"  with  ganglion  cells  at  its  nodeS,  occurs 


Fig.  182. — Horizontal  section  of  a  small  fragment  of  the  mucous  membrane,  including  one  entire 
crypt  of  Lieberkuhn  and  parts  of  several  others:  a,  cavity  of  the  tubular  glands  or  crypts;  6,  one 
of  the  hning  epithelial  cells;  c.  the  lymphoid  or  retiform  spaces,  of  which  some  are  empty,  and  others 
occupied  by  lymph  cells,  as  at  d. 

in  the  submucous  tissue  from  the  stomach  to  the  anus.  From  the  posi- 
tion of  this  plexus  and  the  distribution  of  its  branches,  it  seems  highly 
probable  that  it  is  the  local  centre  for  regulating  the  calibre  of  the  blood- 
vessels supplying  the  intestinal  mucous  membrane,  and  presiding  over  the 
processes  of  secretion  and  absorption. 

(4)  The  mucous  membrane  is  the  most  important  coat  in  relation  to 
the  function  of  digestion.  The  following  structures,  Avhich  enter  into  its 
composition,  may  now  be  successively  described; — the  valvules  conniventes; 
the  villi;  and  the  glands.  The  general  structure  of  the  mucous  mem- 
brane of  the  intestines  resembles  that  of  the  stomach  (p.  241),  and,  like 
it,  is  lined  on  its  inner  surface  by  columnar  epithelium.  Adenoid  tissue 
(Fig.  182,  c  and  cl)  enters  largely  into  its  construction;  and  on  its  deep 
surface  is  the  muscularis  mucoscB  {m  m,  Fig.  183),  the  fibres  of  which  are 
arranged  in  two  layers:  the  outer  longitudinal  and  the  inner  circular. 

Valvulae  Conniventes. — The  valvulce  conniventes  (Fig.  184)  com- 
mence in  the  duodenum,  about  one  or  two  inches  beyond  the  pylorus,  and 
becoming  larger  and  more  numerous  immediately  beyond  the  entrance  of 
the  bile  duct,  continue  thickly  arranged  and  well  developed  throughout 


256 


HAND-BOOK  OF  PIIYSIOLOGY. 


the  jejunum;  then,  gradually  dimmishing  in  size  and  number,  they  cease 
near  the  middle  of  the  ileum.  They  are  formed  by  a  doubling  inward  of 
the  mucous  membrane;  the  crescentic,  nearly  circular,  folds  thus  formed 
being  arranged  transversely  to  the  axis  of  the  intestine,  and  each  indi- 
vidual fold  seldom  extending  around  more  than  J~  or  |  of  the  bowel's  cir- 
cumference. Unlike  the  rugae  in  the  oesophagus  and  stomach,  they  do 
not  disappear  on  distension  of  the  canal.  Only  an  imperfect  notion  of 
their  natural  position  and  function  can  be  obtained  by  looking  at  them 
after  the  intestine  has  been  laid  open  in  the  usual  manner.    To  under- 


Fig.  183.  Fig.  184. 


Fig.  183.— Vertical  section  through  portion  of  small  intestine  of  dog.  two  villi  showing  e,  epithe- 
lium; g,  goblet  cells.  The  free  surface  is  seen  to  be  formed  by  the  "striated  basilar  border,"  while 
inside  the  villus  the  adenoid  tissue  and  unstriped  muscle-cells  are  seen;  Z/,  Lieberkiihn's  folhcles:  ?>i 
m,  muscularis  mucosae,  sending  up  fibr-es  between  the  follicles  into  the  vilh;  sm,  submucous  tissue; 
containing  (gm),  ganglion  cells  of  Meissner's  plexus.  (Schofield.) 

Fig.  184.— Piece  of  small  intestine  (previously  distended  and  hardened  by  alcohol)  laid  open  to 
show  the  normal  position  of  the  valvulse  conniventes. 

stand  them  aright,  a  piece  of  gut  should  be  distended  either  Avith  air  or 
alcohol,  and  not  opened  until  the  tissues  have  become  hardened.  On 
then  making  a  section  it  will  be  seen  that,  instead  of  disappearing,  they 
stand  out  at  right  angles  to  the  general  surface  of  the  mucous  membrane 
(Fig.  184).  Their  functions  arc  probably  less — Besides  (1)  offering  a 
largely  increased  surface  for  secretion  and  absorption,  they  probably  (2) 
prevent  the  too  rapid  passage  of  the  very  liquid  products  of  gastric  diges- 
tion, immediately  after  their  escape  from  the  stomach,  and  (3),  by  their 
projection,  and  consequent  interference  with  a  uniform  and  untroubled 
current  of  the  intestinal  contents,  probably  assist  in  the  more  perfect 
mingling  of  the  latter  witli  the  secretions  })ourcd  out  to  act  on  thorn. 


DIGESTION. 


257 


Glands  of  the  Small  Intestine.— The  glands  are  of  three  princi- 
pal kinds: — viz.,  those  of  (1)  Lieberkiihn,  (2)  Brunner,  and  (3)  Peyer. 

(1.)  The  glands  or  crypts  of  Lieherkuhn  are  simple  tubular  depressions 
of  the  intestinal  mucous  membrane,  thickly  distributed  over  the  whole  sur- 
face both  of  the  large  and  small  intestines.  In  the  small  intestine  they 
are  visible  only  with  the  aid  of  a  lens;  and  their  orifices  appear  as  minute 
dots  scattered  between  the  villi.  They  are  larger  in  the  large  intestine, 
and  increase  in  size  the  nearer  they  approach  the  anal  end  of  the  intes- 
tinal tube;  and  in  the  rectum  their  orifices  may  be  visible  to  the  naked 
eye.  In  length  they  vary  from  3V  to  of  a  line.  Each  tubule  (Fig. 
186)  is  constructed  of  the  same  essential  parts  as  the  intestinal  mucous 
membrane,  viz.,  a  fine  membrana  propria,  or  basement  membrane,  a 


« 


Fig.  185.  Fig.  186. 

Fig.  185.— Transverse  section  through  four  crypts  of  Lieberkiihn  from  the  large  intestine  of  the 
pig.  They  are  hned  by  columnar  epithelial  cells,  the  nuclei  being  placed  in  the  outer  part  of  the 
cells.  The  divisions  between  the  cells  are  seen  as  lines  radiating  from  L,  the  lumen  of  the  crypt;  G, 
epithehal  cells,  which  have  become  transformed  into  goblet  cells.    X  350.   (IQein  and  Noble  Smith.) 

Fig.  186.— a  gland  of  Lieberkiihn  in  longitudinal  section.  (Brinton.) 

layer  of  cylindrical  epithelium  lining  it,  and  capillary  blood-vessels  cover- 
ing its  exterior,  the  free  surface  of  the  columnar  cells  -presenting  an 
appearance  precisely  similar  to  the  '^striated  basilar  border"  which  covers 
the  villi.  Their  contents  appear  to  vary,  even  in  health;  the  varieties 
being  dependent,  probably,  on  the  period  of  time  in  relation  to  digestion 
at  which  they  are  examined. 

Among  the  columnar  cells  of  Lieberkiihn's  follicles,  goblet-cells  fre- 
quently occur  (Fig.  185). 

(2.)  Brunner' s  glands  (Fig.  188)  are  confined  to  the  duodenum;  the}^ 
are  most  abundant  and  thickly  set  at  the  commencement  of  this  portion 
of  the  intestine,  diminishing  gradually  as  the  duodenum  advances.  They 
are  situated  beneath  the  mucous  membrane,  and  imbedded  in  the  submu- 
cous tissue,  each  gland  is  a  branched  and  convoluted  tube,  lined  with 
columnar  epithelium.  As  before  said,  in  structure  they  are  very  similar 
to  the  pyloric  glands  of  the  stomach,  and  their  epithelium  undergoes  a 
Vol.  I.— 17. 


258 


HAND-BOOK  OF  PHYSIOLOGY. 


similar  cluiiige  during  secretion;  but  they  are  more  branched  and  convo- 
hited  and  their  ducts  are  longer.  (AVatney.)  The  duct  of  each  gland 
passes  through  the  muscularis  mucosae,  and  opens  on  the  surface  of  the 
mucous  membrane. 

(3.)  The  glands  of  Peyer  occur  chiefly  but  not  exclusively  in  the  small 
intestine.    They  are  found  in  greatest  abundance  in  the  lower  part  of  the 


Fig.  187.  Fig.  188. 

Fig.  187.— Transverse  section  of  injected  Peyer''s  glands  (from  Kolliker).  The  drawing  was  taken 
from  a  preparation  made  byFrey:  it  represents  the  fine  capillary -looped  network  spreading  from 
the  surroimding  blood-vessels  into  the  interior  of  three  of  Peyser's  capsules  from  the  intestine  of  the 
rabbit. 

Fig.  188.— Vertical  section  of  duodenum,  sho^^'ing  a,  viUi;  &,  crypts  of  Lieberkiihn,  and  c,  Bi-uu- 
ner's  glands  in  the  submucosa  s,  with  ducts,  d:  muscularis  mucosae,  m\  and  circular  muscular  coat/. 
(Schofield.) 

ileum  near  to  the  ileo-cgecal  valve.  They  are  met  with  in  two  conditions, 
viz.,  either  scattered  singly,  in  which  case  they  are  termed  glandular  soli- 
taricB,  or  aggregated  in  groups  varying  from  one  to  three  inches  in  length 
and  about  half-an-inch  in  width,  chiefly  of  an  oval  form,  their  long  axis 
parallel  with  that  of  the  intestine.  In  this  state, they  are  named  glandulw 
agminatcB,  the  groups  being  commonly  called  Peyefs  patches  (Fig.  189), 
and  almost  always  placed  opposite  the  attachment  of  the  mesentery.  In 
structure,  and  in  function,  there  is  no  essential  difference  between  the 
solitary  glands  and  the  individual  bodies  of  which  each  §roup  or  patch  is 
made  up.    They  are  really  single  or  aggregated  masses  of  adenoid  tissue 


DIGESTION. 


25'J 


forming  lymph-follicles.  In  the  condition  in  which  they  have  been  most 
commonly  examined,  each  gland  appears  as  a  circular  opaque-white 
rounded  body,  from  to  -^^  i^^^  diameter,  according  to  the  degree  in 
which  it  is  developed.  They  are  principally  contained  in  the  submucous 
coat,  but  sometimes  project  through  the  musciilaris  mucosce  into  the 
mucous  membrane.  In  the  agminate  glands,  each  follicle  reaches  the 
free  surface  of  the  intestine,  and  is  covered  Avith  columnar  eioithelium. 
Each  gland  is  surrounded  by  the  openings  of  Lieberkuhn^s  follicles. 

The  adjacent  glands  of  a  Peyer  s  patch  are  connected  together  by  ade- 
noid tissue.  Sometimes  the  lymphoid  tissue  reaches  the  free  surface, 
replacing  the  epithelium,  as  is  also  the  case  with  some  of  the  lymphoid 
follicles  of  the  tonsil  (p.  236). 

Peyer^s  glands  are  surrounded  by  lymphatic  sinuses  which  do  not 
penetrate  into  their  interior;  the  interior  is,  however,  traversed  by  a  very 
rich  blood  capillary  plexus.  If  tlie  vermiform  appendix  of  a  rabbit,  which 
consists  largely  of  Peyer's  glands,  be  injected  with  blue,  by  pressing  the 


,            .     ■  ....V 

Fig.  189.— Agminate  follicles,  or  Peyer's  patch,  in  a  state  of  distension,    x  5.  (Boehm.) 

point  of  a  fine  syringe  into  one  of  the  lymphatic  sinuses,  the  Peyer's 
glands  will  appear  as  greyish  white  spaces  surrounded  by  blue;  if  now  the 
arteries  of  the  same  be  injected  with  red,  the  greyish  patches  will  change 
to  red,  thus  proving  that  they  are  surrounded  by  lymphatic  spaces,  but 
penetrated  by  blood-vessels.  The  lacteals  passing  out  of  the  villi  commu- 
nicate with  the  lymph  sinuses  round  Peyer^s  glands. 

It  is  to  be  noted  that  they  are  largest  and  most  prominent  in  children 
and  young  persons. 

Villi.— The  Villi  (Figs.  183,  188,  190,  and  191),  are  confined  exclu- 
sively to  the  mucous  membrane  of  the  small  intestine.  They  are  minute 
vascular  processes,  from  a  quarter  of  a  line  to  a  line  and  two-thirds  in 
length,  covering  the  surface  of  the  mucous  membrane,  and  giving  it  a 
peculiar  velvety,  fleecy  appearance.  Krause  estimates  them  at  fifty  to 
ninety  in  number  in  a  square  line,  at  the  upper  part  of  the  small  intes- 


260 


HAND-BOOK  OF  PHYSIOLOGY. 


tine,  and  at  forty  to  seventy  in  the  same  area  at  the  lower  part.  They 
vary  in  form  even  in  the  same  animal,  and  dilfer  according  as  the  lym- 
phatic vessels  they  contain  are  empty  or  fnll  of  chyle;  being  usually,  in 
the  former  case,  flat  and  pointed  at  their  summits,  in  the  latter  cylindri- 
cal or  cleavate. 

Each  villus  consists  of  a  small  projection  of  mucous  membrane,  and 
its  interior  is  therefore  supported  throughout  by  fine  adenoid  tissue,  which 
forms  the  framework  or  stroma  in  which  the  other  constituents  are  con- 
tained. 

The  surface  of  the  villus  is  clothed  by  columnar  epithelium,  which 
rests  on  a  fine  basement  membrane;  while  within  this  are  found,  reckon- 
ing from  without  inward,  blood-vessels,  fibres  of  the  muscularis  ^nucosce, 
and  a  single  lymphatic  or  lacteal  vessel  rarely  looped  or  branched  (Fig. 
192);  besides  granular  matter,  fat-globules,  etc. 


Fig.  190.  Fig.  191. 

Fig.  190.— Section  of  small  intestine  showing  villi,  Lieberkiihn's  glands  and  a  Peyer's  solitary 
gland,   m,  m,  muscularis  mucosa.   (Klein  and  Noble  Smith.) 

Fig.  1»91. — Vertical  section  of  a  viUus  of  the  small  intestine  of  a  cat.  a,  striated  basilar  border  of 
the  epithelium ;  h.  columnar  epithelium ;  c,  goblet  cells ;  ,  central  lymph-vessel ;  e,  smooth  muscular 
fibres;  /,  adenoid  stroma  of  the  villus  in  which  lymph  corpuscles  lie.  (Klein.) 

The  epithelium,  is  of  the  columnar  kind,  and  continuous  with  that 
lining  the  other  parts  of  the  mucous  membrane.  The  cells  are  arranged 
with  their  long  axis  radiating  from  the  surface  of  the  villus  (Fig.  191), 
and  their  smaller  ends  resting  on  the  basement  membrane.  The  free 
surface  of  the  epithelial  cells  of  the  villi,  like  that  of  the  cells  which  cover 
the  general  surface  of  the  mucous  membrane,  is  covered  by  a  fine  border 
which  exhibits  very  delicate  striations,  whence  it  derives  its  name,  ''stria- 
ted basilar  border." 

Beneath  the  basement  or  limiting  membrane  there  is  a  ricli  supply  of 
blood-vessels.  Two  or  more  minute  arteries  are  distributed  within  each 
villus;  and  from  their  capillaries,  which  form  a  dense  network,  proceed 
one  or  two  small  veins,  which  pass  out  at  the  base  of  the  villus. 

The  layer  of  the  muscularis  mucosm  in  the  villus  forms  a  kind  of  thin 
hollow  cone  immediately  around  the  central  lacteal,  and  is,  therefore, 


DIGESTION. 


261 


situate  beneath  the  blood-vessels.  It  is  without  doubt  instrumental  in 
the  propulsion  of  chyle  along  the  lacteal. 

The  lacteal  vessel  enters  the  base  of  each  villus,  and  passing  up  in  the 
middle  of  it,  extends  nearly  to  the  tip,  where  it  ends  commonly  by  a 
closed  and  somewhat  dilated  extremity.  In  the  larger  villi  there  may  be 
two  small  lacteal  vessels  which  end  by  a  loop  (Fig.  192),  or  the  lacteals 
may  form  a  kind  of  network  in  the  villus.  The  last  method  of  ending, 
however,  is  rarely  or  never  seen  in  the  human  subject,  although  common 
in  some  of  the  lower  animals  (a.  Fig.  192). 


Fig.  192.— a.  Villus  of  sheep.   B.  Villi  of  man.   (Slightly  altered  from  Teichmann.) 

The  office  of  the  villi  is  the  absorption  of  chyle  and  other  liquids  from 
the  intestine.  The  mode  in  which  they  affect  this  will  be  considered  in 
the  Chapter  on  Absorption. 

II.  The  Large  Intesitine. — The  Large  Intestine,  which  in  an  adult  is 
from  about  4  to  6  feet  long,  is  subdivided  for  descriptive  purposes  into 
three  portions  (Fig.  165),  viz. : — the  cmcum,  a  short  wide  pouch,  commu- 
nicating with  the  lower  end  of  the  small  intestine  through  an  opening, 
guarded  by  the  ileo-cmcal  valve;  the  colon,  continuous  with  the  caecum, 
which  forms  the  principal  part  of  the  large  intestine,  and  is  divided  into 
an  ascending,  transverse  and  descending  portion:  and  the  rectum,  Avhich, 
after  dilating  at  its  lower  part,  again  contracts,  and  immediately  afterward 


262 


HAND-BOOK  OF  PHYSIOLOGY. 


opens  externally  through  the  emus.  Attached  to  the  csecum  is  the  small 
appendix  vermiformis. 

Structure. — Like  tlie  swall  intestine,  the  large  is  constructed  of  four 
principal  coats,  viz.,  the  serous,  muscular,  submucous,  and  mucous.  The 
serous  coat  need  not  be  here  particularly  described.  Connected  with  it 
are  the  small  processes  of  peritoneum,  containing  fat,  called  ap)pendices 
epiploiccB.  The  fibres  of  tlie  muscular  coat,  like  those  of  the  small  in- 
testine, are  arranged  in  two  layers — the  outer  longitudinal,  the  inner  circu- 
lar. In  the  caecum  and  colon,  the  longitudinal  fibres,  besides  being,  as 
in  the  small  intestine,  thinly  disposed  in  all  parts  of  the  wall  of  the  bowel. 


Fig.  193.— Diagram  of  lacteal  vessels  in  small  intestine,  a,  lacteals  in  villi ;  p,  Payer's  glands;  b 
and  D,  superficial  and  deep  network  of  lacteals  in  submucous  tissue;  l,  Lieberkuhn's  glands ;  e,  small 
branch  of  lacteal  vessel  on  its  way  to  mesenteric  gland;  h  and  o,  muscular  fibres  of  intestine;  s,  peri- 
toneum. (Teichmann.) 


are  collected,  for  the  most  part,  into  three  strong  bands,  which  being 
shorter,  from  end  to  end,  than  the  other  coats  of  the  intestine,  hold  the 
canal  in  folds,  bounding  intermedia,te  sacculi.  On  the  division  of  these 
bands,  the  intestine  can  be  drawn  out  to  its  full  length,  and  it  then  ns- 
sumes,  of  course,  a  uniformly  cylindrical  form.  In  tlie  rectum,  the  fas- 
ci(;uli  of  these  longitudinal  bands  spread  out  and  mingle  with  the  other 
longitudinal  fibres,  forming  with  them  a  thicker  layer  of  libres  than  exists 
on  any  other  part  of  the  intestinal  canal.  The  circular  uniscular  fibres 
are  spread  over  the  whole  surface  of  tlie  bowel,  but  are  somewhat  more 


DIGESTION. 


marked  in  the  intervals  between  the  sacculi.  Toward  the  lower  end  of 
the  rectum  they  become  more  numerous,  and  at  the  anus  they  form  a 
strong  band  called  the  internal  sphincter  muscle. 

The  mucous  'membrane  of  the  large,  like  that  of  the  small  intestine,  is 
lined  throughout  by  columnar  epithelium,  but,  unlike  it,  is  quite  smooth 
and  destitute  of  villi,  and  is  not  projected  in  the  form  of  valvules  conni- 
ventes.  Its  general  microscopic  structure  resembles  that  of  the  small  in- 
testine: and  it  is  bounded  below  by  the  muscularis  mucosce. 

The  general  arrangement  of  ganglia  and  nerve-fibres  in  the  large  in- 
testine resembles  that  in  the  small  (p.  255). 

Glands  of  the  Large  Intestine. — The  glands  with  which  the 
large  intestine  is  provided  are  of  two  kinds,  (1)  the  tubular  and  (2)  the 
lymphoid. 


I 


a 

Fig.  194.— Horizontal  section  through  a  portion  of  the  mucous  membrane  of  the  large  intestine, 
showing  Lieberkiihn''s  glands  in  transverse  section,  a,  lumen  of  gland— Uning  of  columnar  cells 
with  c,  goblet  cells,  6,  supporting  connective  tissue.   Highly  magnified.   (V.  D.  Harris.) 

(1.)  The  tubular  glands,  or  glands  of  Lieberkiihn,  resemble  those  of 
the  small  intestine,  but  are  somewhat  larger  and  more  numerous.  They 
are  also  more  uniformly  distributed. 

(2.)  Follicles  of  adenoid  or  lymphoid  tissue  are  most  numerous  in  the 
caecum  and  vermiform  appendix.  They  resemble  in  shape  and  structure^ 
almost  exactly,  the  solitary  glands  of  the  small  intestine. 

Peyer^s  patches  are  not  found  in  the  large  intestine. 

Ileo-Caecal  Valve. — The  ileo-caecal  valve  is  situate  at  the  place  of 
junction  of  the  small  with  the  large  intestine,  and  guards  against  any  re- 
flex of  the  contents  of  the  latter  into  the  ileum.  It  is  composed  of  two 
semilunar  folds  of  mucous  membrane*  Each  fold  is  formed  by  a  doubling 
inward  of  the  mucous  membrane,  and  is  strengthened  on  the  outside  by 


264 


HAND-BOOK  OF  PHYSIOLOGY. 


some  of  the  circular  muscular  fibres  of  the  intestine,  which  are  contained 
between  the  cuter  surfaces  of  the  two  layers  of  which  each  fold  is  composed. 
While  the  circular  muscular  fibres,  however,  of  the  bowel  at  the  junction 
of  the  ileum  witli  the  csecum  are  contained  between  the  outer  opposed 
surfaces  of  the  folds  of  mucous  membrane  which  form  the  valve,  the 
longitudinal  muscular  fibres  and  the  peritoneum  of  the  small  and  large 
intestine  respectively  are  continuous  with  each  other,  without  dipping 
in  to  follow  the  circular  fibres  and  the  mucous  membrane.  In  this  man- 
ner, therefore,  the  folding  inward  of  these  two  last-named  structures  is 
preserved,  while,  on  the  other  hand,  by  dividing  the  longitudinal  muscu- 
lar fibres  and  the  peritoneum,  the  valve  can  be  made  to  disappear,  just 
as  the  constrictions  between  the  sacculi  of  the  large  intestine  can  be 
made  to  disappear  by  performing  a  similar  operation.  The  inner  surface 
of  the  folds  is  smooth;  the  mucous  membrane  of  the  ileum  being  con- 
tinuous with  that  of  the  caecum.  That  surface  of  each  fold  which  looks 
toward  the  small  intestine  is  covered  with  villi,  while  that  which  looks  to 
the  caecum  has  none.  "When  the  caecum  is  distended,  the  margin  of  the 
folds  are  stretched,  and  thus  are  brought  into  firm  apposition  one  with 
the  other. 

DlGESTIOl^"  11^"  THE  InTESTIHTES. 

After  the  food  has  been  duly  acted  upon  by  the  stomach,  such  as  has 
not  been  absorbed  passes  into  the  duodenum,  and  is  there  subjected  to 
the  action  of  the  secretions  of  the  pancreas  and  liver,  which  enter  that 
portion  of  the  small  intestine.  Before  considering  the  changes  which 
the  food  undergoes  in  consequence,  attention  should  be  directed  to  the 
structure  and  secretion  of  these  glands,  and  to  the  secretion  (succus  en- 
tericus)  w^iich  is  poured  out  into  the  intestines  from  the  glands  lining 
them. 

The  Pajtckeas,  akd  its  Secketion". 

The  Pancreas  is  situated  within  the  curve  formed  by  the  duodenum; 
and  its  main  duct  opens  into  that  part  of  the  small  intestine,  through  a 
small  opening,  or  through  a  duct  common  to  it  and  to  the  liver,  about 
two  and  a  half  inches  from  the  pylorus. 

Structure. — In  structure  the  pancreas  bears  some  resemblance  to  the 
salivary  glands.  Its  capsule  and  septa,  as  well  as  the  blood-vessels  and 
lymphatics,  are  similarly  distributed.  It  is,  however,  looser  and  softer, 
the  lobes  and  lobules  being  less  compactly  arranged.  The  main  duct 
divides  into  branches  (lobar  ducts),  one  for  each  lobe,  and  these  branches 
subdivide  into  intralobular  ducts,  and  these  again  by  their  division  and 
branching  form  the  gland  tissue  proper.    The  intralobular  ducts  corre- 


DIGESTION. 


265 


spond  to  a  lobule,  while  between  them  and  the  secreting  tubes  or  alveoli 
are  longer  or  shorter  intermediary  ducts.  The  larger  ducts  possess  a 
very  distinct  lumen  and  a  membrana  propria  lined  with  columnar  epi- 
thelium, the  cells  of  which  are  longitudinally  striated,  but  are  shorter 
than  those  found  in  the  ducts  of  the  salivary  glands.  In  the  intralobular 
ducts  the  epithelium  is  short  and  the  lumen  is  smaller.  The  intermediary 
ducts  opening  into  the  alveoli  possess  a  distinct  lumen,  with  a  membrana 
propria  lined  with  a  single  layer  of  flattened  elongated  cells.  The  alveoli 
are  branched  and  convoluted  tubes,  with  a  membrana  propria  lined  with 
a  single  layer  of  columnar  cells.  They  have  no  distinct  lumen,  its  place 
being  taken  by  fusiform  or  branched  cells.  Heidenhain  has  observed 
that  the  alveoli  cells  in  the  pancreas  of  a  fasting  dog  consist  of  two  zones, 
an  inner  or  central  zone,  which  is  finely  granular,  and  which  stains  feebly. 


Fig.  195. — Section  of  the  pancreas  of  a  dog  during  digestion,  a,  alveoli  lined  with  ceUs,  the  outer 
zone  of  which  is  well  stained  with  haematoxyUn ;  d,  intermediary  duct  lined  with  squamous  epithehum. 
X  350.   (Klein  and  Noble  Smith.) 

and  a  smaller  parietal  zone  of  finely  striated  protoplasm,  which  stains 
easily.  The  nucleus  is  partly  in  one,  partly  in  the  other  zone.  During 
digestion,  it  is  found  that  the  outer  zone  increases  in  size,  and  the  central 
zone  diminishes;  the  cell  itself  becoming  smaller  from  the  discharge  of 
the  secretion.  At  the  end  of  digestion  the  first  condition  again  appears, 
the  inner  zone  enlarging  at  the  expense  of  the  outer.  It  appears  that  the 
granules  are  formed  by  the  protoplasm  of  the  cells,  from  material  supplied 
to  it  by  the  blood.  The  granules  are  thought  to  be  not  the  ferment 
itself,  but  material  from  which,  under  certain  conditions,  the  ferments  of 
the  gland  are  made,  and  therefore  called  Zymogen. 

Pancreatic  Secretion. — The  secretion  of  the  pancreas  has  been  ob- 
tained for  purposes  of  experiment  from  the  lower  animals,  especially  the 
dog,  by  opening  the  abdomen  and  exposing  the  duct  of  the  gland,  which 
is  then  made  to  communicate  with  the  exterior.  A  pancreatic  fistula  is 
thus  established. 


266 


HAND-BOOK  OF  PHYSIOLOGY. 


An  extract  of  pancreas  made  from  the  gland,  which  has  been  removed 
from  an  animal  killed  during  digestion,  possesses  the  active  properties  of 
pancreatic  secretion;  It  is  made  by  first  dehj^drating  the  gland,  which 
has  been  cut  up  into  small  pieces,  by  keeping  it  for  some  days  in  absolute 
alcohol,  and  then,  after  the  entire  removal  of  the  alcohol,  placing  it  in 
strong  glycerin.  A  glycerin  extract  is  thus  obtained.  It  is  a  remarkable 
fact,  however,  that  the  amount  of  the  ferment  tri/psin  greatly  increases 
if  the  gland  be  exposed  to  the  air  for  twenty-four  hours  before  placing  in 
alcohol;  indeed,  a  glycerin  extract  made  from  the  gland  immediately 
upon  removal  from  the  body  often  appears  to  contain  none  of  that  fer- 
ment. This  seems  to  indicate  that  the  conversion  of  zymogen  in  the 
gland  into  the  ferment  only  takes  place  during  the  act  of  secretion,  and 
that  the  gland,  although  it  always  contains  in  its  cells  the  materials  (tryp- 
sinogen)  out  of  which  trypsin  is  formed,  yet  the  conversion  of  the  One 
into  the  other  only  takes  place  by  degrees.  Dilute  acid  appears  to  assist 
and  accelerate  the  conversion,  and  if  a  recent  pancreas  be  rubbed  up  with 
dilute  acid  before  dehydration,  a  glycerin  extract  made  afterward,  even 
though  the  gland  may  have  been  only  recently  removed  from  the  body,  is 
very  active. 

Properties. — Pancreatic  juice  is  colorless,  transparent,  and  slightly 
viscid,  alkaline  in  reaction.  It  varies  in  specific  gravity  from  1010  to 
1015,  according  to  whether 'it  is  obtained  from,  a  permanent  fistula — then 
more  watery — or  from  a  newly-opened  duct.  The  solids  vary  in  a  tempo- 
rary fistula  from  80  to  100  parts  per  thousand,  and  in  a  permanent  one 
from  16  to  50  per  thousand. 

Chemical  Composition  op  the  Pancreatic  Secretion. 


From  a  permanent  fistula.  (Bernstein.) 

Water   .975 

Solids — Ferments : 

Proteids,  including  Serum — Albumin,  Casein,  )  ^ 

Leucin  and  Tyrosin,  Fats  and  Soaps     .  ) 
Inorganic  residue,  especially  Sodium  Carbonate  .  8 

  25 

1000 

Funcfinnfi. — (1.)  It  converts  ^??*o?'^/V/.<?  info  peptones,  iho,  intermediate 
product  being  not  akin  to  syutonin  or  acid-albumin,  as  in  gastric  diges- 
tion, but  to  alkali-albumhi.  Kiihne  believes  that  the  intermediate  pro- 
ducts, both  in  the  pe})tic  and  pancreatic  digestion  of  proteids.  are  two, 
viz.,  antialbumose  and  hemialbumose,  and  tliat  the  peptones  formed  cor- 
respond to  these,  viz.,  antipeptone  and  hemipeptonc.  Tlie  hemipeptone 
is  capable  of  being  converted  by  the  action  of  the  pancreatic  ferment — 


DIGESTION. 


267 


trypsin — into  leucin  and  tyrosin,  but  is  not  so  changed  by  pepsin;  the 
antipeptone  cannot  be  further  split  up.  The  products  of  pancreatic 
digestion  are  sometimes  further  complicated  by  the  appearance  of  certain 
faecal  substances,  of  which  indol  and  naphthilamine  are  the  most  impor- 
tant.   (Kiihne. ) 

When  the  digestion  goes  on  for  a  long  time  the  indol  is  formed  in  con- 
siderable quantities,  and  emits  a  most  disagreeable  faecal  odor,  which  was 
attributed  to  putrefaction  till  Kiihne  showed  its  true  nature.  All  the  al- 
buminous or  proteid  substances  which  have  not  been  converted  into  pep- 
tone, and  absorbed  in  the  stomach,  and  the  partially  changed  substances, 
i.e.,  the  parapeptones,  are  converted  into  peptone  by  the  pancreatic  juice, 
and  then  in  part  into  leucin  and  tyrosin. 

(2.)  Nitrogenous  loclies  other  titan  proteids,  are  not  to  any  eo:tent 
altered.  Mucin  can,  however,  be  dissolved,  but  not  gelatin  or  horny  tis- 
sues. 

(3.)  Starch  is  converted  into  glucose  in  an  exactly  similar  manner  to 
that  which  hajopens  with  the  saliva.  As  mentioned  before,  it  seems  not 
unlikely  that  glucose  is  not  formed  at  once  from  starch,  but  that  certain 
dextrines  are  intermediate  products.  If  the  sugar  which  is  at  first  formed, 
as  is  stated  by  some  chemists,  be  not  glucose  but  maltose,  at  any  rate  the 
pancreatic  juice  after  a  time  completes  the  whole  change  of  starch  into 
glucose.  There  is  a  distinct  amylolytic  ferment  (Amylopsin)  in  the  pan- 
creatic juice  which  cannot  be  distingaished  from  ptyalin. 

(4.)  Oils  and  fats  are  both  emulsified  and  split  up  into  their  fatty 
acids  and  glycerin  ly  pancreatic  secretion.  Even  .f  part  of  this  action  is 
due  to  the  alkalinity  of  the  medium,  it  is  probable  that  there  is  a  third 
distinct  ferment  (Steapsin)  which  facilitates  the  change. 

Several  cases  have  been  recorded  in  which  the  pancreatic  duct  being 
obstructed,  so  that  its  secretion  could  not  be  discharged,  fatty  or  oily 
matter  was  abundantly  discharged  from  the  intestines.  In  nearly  all 
these  cases,  indeed,  the  liver  was  coincidently  diseased,  and  the  change 
or  absence  of  the  bile  might  appear  to  contribute  to  the  result;  yet  the 
frequency  of  extensive  disease  of  the  liver,  unaccompanied  by  fatty  dis- 
charges from  the  intestines,  favors  the  view  that,  in  these  cases,  it  is  to 
the  absence  of  the  pancreatic  fluid  from  the  intestines  that  the  excretion 
or  non-absorption  of  fatty  matter  should  be  ascribed. 

(5.)  It  possesses  the  property  of  curdling  niilh,  containing  a  special 
(rennet)  ferment  for  that  purpose.  The  ferment  is  distinct  from  tr}-psin, 
and  will  act  in  the  presence  of  an  acid  (W.  Roberts). 

Conditions  favorable  to  the  Action  of  the  Pancreatic  Juice.— 
These  are  similar  to  those  which  are  favorable  to  the  action  of  the  saliva, 
and  the  reverse  (p.  231). 


268 


HAND-BOOK  OF  PHYSIOLOGY. 


The  Liver. 

The  Liver,  tlie  largest  gland  in  the  body,  situated  in  the  abdomen, 

chiefly  on  the  right  side,  is  an  extremely  vascular  organ,  and  receives  its 
supply  of  blood  from  two  distinct  vessels,  the  portal  vein  and  hepatic  ar- 
tery, while  the  blood  is  returned  from  it  into  the  vena  cava  inferior  by 
the  hepatic  veins.  Its  secretion,  tlie  hiJe,  is  conveyed  from  it  by  the 
hepatic  duct,  either  directly  into  the  intestine,  or,  when  digestion  is  not 
going  on,  into  the  cystic  duct,  and  thence  into  the  gall-bladder,  where  it 


Fig.  196.— The  under  surface  of  the  hver.  g.  b.,  gall-bladder:  h.  d.,  common  bUe-duct;  h.  a., 
hepatic  artery;  v.  p..  portal  vein:  l.  q..  lobulus  quadratus:  l.  s..  lobulus  spigelii;  l.  c,  lobulus  cau- 
datus;  d.  v.,  ductus  venosus ;  u.  v.,  xunbilical  vein.   (Noble  Smith.) 

accumulates  until  required.  The  portal  vein,  hepatic  artery,  and  hepatic 
duct  branch  together  throughout  the  liver,  while  the  hepatic  veins  and 
their  tributaries  run  by  themselves. 

On  the  outside  the  liver  has  an  incomplete  covering  of  peritoneum, 
and  beneath  this  is  a  very  fine  coat  of  areolar  tissue,  continuous  over  the 
whole  surface  of  the  organ.  It  is  thickest  where  the  peritoneum  is  absent, 
and  is  continuous  on  the  general  surface  of  the  liver  with  the  fine  and, 
in  the  human  subject,  almost  imperceptible,  areolar  tissue  investing  the 
lobules.  At  the  transverse  fissure  it  is  merged  in  the  areolar  investment 
called  Glisson's  capsule,  Avhich,  surrounding  the  portal  vein,  hepatic  ar- 
tery, and  hepatic  dnct,  as  they  enter  at  this  part,  accompanies  them  in 
their  brancliins^s  throuorh  the  substance  of  the  liver. 

Structure. — The  liver  is  made  up  of  small  roundish  or  oval  portions 
called  lobules,  each  of  which  is  about  '^^^  \\\q\\  in  diameter,  and  com- 
posed of  the  minute  brandies  of  tlie  portal  vein,  liopatic  artery,  hepatic 
duct,  and  hepatic  vein;  while  the  interstices  of  these  vessels  are  lilled 
by  the  liver  cells.  The  hepatic  cells  (Fig.  197),  which  form  the  glandular 
or  secreting  part  of  the  liver,  are  of  a  spheroidal  form,  somewhat  polyg- 


DIGESTION. 


269 


onal  from  mutual  pressure  about  g  j-o  to  ^-^^-^  inch  in  diameter,  possess- 
ing one,  sometimes  two  nuclei.  The  cell-substance  contains  numerous 
fatty  molecules,  and  some  yellowish-brown  granules  of  bile-pigment.  The 
cells  sometimes  exhibit  slow  amoeboid  movements.  They  are  held  to- 
gether by  a  very  delicate  sustentacular  tissue,  continuous  with  the  inter- 
lobular connective  tissue. 

To  understand  the  distribution  of  the  blood-vessels  in  the  liver,  it 
will  be  well  to  trace,  first,  the  two  blood-vessels  and  the  duct  which  enter 
the  organ  on  the  under  surface  at  the  transverse  fissure,  viz.,  the  portal 
vein,  hepatic  artery,  and  hepatic  duct.  As  before  remarked,  all  three 
l-^n  in  company,  and  their  appearance  on  longitudinal  section  is  shown  in 


Fig.  197.  Fig.  198. 


Fig.  197. — A.  Liver-cells.   B,  Ditto,  containing  various  sized  particles  of  fat. 

Fig.  198.— Longitudinal  section  of  a  portal  canal,  containing  a  portal  vein,  hepatic  artery  and 
hepatic  duct,  from  the  pig.  p,  branch  of  vena  portse,  situate  in  a  portal  canal  formed  amongst  the 
lobules  of  the  Uver,  1 1,  and  giving  off  vaginal  branches;  there  are  also  seen  within  the  large  portal 
vein  numerous  orifices  of  the  smallest  interlobular  veins  arising  directly  from  it;  a,  hepatic  artery; 
d,  hepatic  duct.    X  5.  (Kiernan.) 

Fig.  198.  Eunning  together  through  the  substance  of  the  liver,  they  are 
contained  in  small  channels  called  portal  canals,  their  immediate  invest- 
ment being  a  sheath  of  areolar  tissue  (Glisson^s  capsule). 

To  take  the  distribution  of  the  portal  vein  first: — In  its  course  through 
the  liver  this  vessel  gives  off  small  branches  which  divide  and  subdivide 
between  the  lobules  surrounding  them  and  limiting  them,  and  from  this 
circumstance  called  inter-lohulsLY  veins.  From  these  small  vessels  a  dense 
capillary  network  is  prolonged  into  the  substance  of  the  lobule,  and  this 
network,  gradually  gathering  itself  up,  so  to  speak,  into  larger  vessels, 
converges  finally  to  a  single  small  vein,  occupying  the  centre  of  the  lobule, 
and  hence  called  intra-lobulsiY.  This  arrangement  is  well  seen  in  Fig. 
199,  which  represents  a  transverse  section  of  a  lobule. 


270 


HAND-BOOK  OF  PHYSIOLOGY. 


The  small  m^m-lobular  veins  discharge  their  contents  into  veins  called 
5W^-lobular  {Jilili,  Fig.  200);  while  these  again,  by  their  union,  form 


Fig.  199.— Cross-section  of  a  lobiole  of  the  human  hver,  in  which  the  capillary  network  between 
the  portal  and  hepatic  veins  has  been  fuUy  injected.  1,  section  of  the  nif  >-a-lobular  vein;  2,  its  smaller 
branches  collecting  blood  from  the  capillary  network;  3,  infe?--lobular  branches  of  the  vena  portae 
with  their  smaller  ramifications  passing  inward  toward  the  capillary  network  in  the  substance  of 
the  lobule,    x  60.  (Sappey.) 


Fia.  200.— Section  of  a  portion  of  liver  passing  longitudinally  through  a  considerable  hepatic  vein, 
from  the  pig.  h,  hepatic  venous  trunk,  jigaiiist  which  the  sides  of  the  lobules  (/)  are  applied:  h,  /i.  /i, 
sublobular  hepatic  veins,  ou  which  tlie  bases  of  the  lobules  rest,  and  through  the  coats  of  which  they 
are  seen  as  polygoual  figtuvs;  /,  mouth  of  the  intralobular  veins,  ojiening  into  the  sublobular  veins; 
i' ,  intralobular  veins  shown  passmg  up  the  centre  of  some  divideil  lobules;  /,  /,  cut  surface  of  the 
liver;  c,  c,  walls  of  the  hepatic  venous  canal,  formed  by  the  polygonal  bases  or  the  lobules.  X  5. 
(Kiernan.) 

tlie  main  branches  of  the  hepatic  veins,  which  leave  the  ])osterior  border 
of  the  liver  to  end  by  two  or  tlireo  principal  ti-imks  in  the  interior  vena 


DIGESTIOl^T. 


271 


cava,  just  before  its  passage  through  the  diaphragm.  The  sub-lohuVdr 
and  hepatic  veins,  unlike  the  portal  vein  and  its  companions,  have  little 
or  no  areolar  tissue  around  them,  and  their  coats  being  very  thin,  they 
form  little  more  than  mere  channels  in  the  liver  substance  which  closely 
surrounds  them. 

The  manner  in  which  the  lobules  are  connected  with  the  sul-lohular 
veins  by  means  of  the  small  intra-lobidar  veins  is  well  seen  in  the  diagram 
(Fig.  200  and  in  Fig.  201),  which  represent 
the  parts  as  seen  in  a  longitudinal  section. 
The  appearance  has  been  likened  to  a  twig 
having  leaves  without  footstalks — the  lobules 
representing  the  leaves,  and  the  sub-lobular 
vein  the  small  branch  from  which  it  springs. 
On  a  transverse  section,  the  appearance  of  the 
intra-lohular  veins  is  that  of  1,  Fig.  199, 
while  both  a  transverse  and  longitudinal  sec- 
tion are  exhibited  in  Fig.  176. 

The  hepatic  artery,  the  function  of  which 
is  to  distribute  blood  for  nutrition  to  Glisson^s 
capsule,  the  walls  of  the  ducts  and  blood- 
vessels, and  other  parts  of  the  liver,  is  distrib- 
uted in  a  very  similar  manner  to  the  portal 
vein,  its  blood  being  returned  by  small  branches  either  into  the  rami- 
fications of  the  portal  vein,  or  into  the  capillary  plexus  of  the  lobules 
which  connects  the  inter  and  intra  lobular  veins. 


Irobuiss 


£obul( 


Fig 


Diagram  showing  the 
manner  in  which  the  lobules  of  the 
liver  rest  on  the  sublobiilar  veins. 
(After  Kiernan.) 


Fig.  202.— Capillary  network  of  the  lobules  of  the  rabbit's  liver.  The  figure  is  taken  from  a  very- 
successful  injection  of  the  hepatic  veins,  made  by  Harting:  it  shows  nearly  the  whole  of  two  lobules, 
and  parts  of  three  others;  jo,  portal  branches  running  in  the  interlobular  spaces;  h,  hepatic  veins  pen- 
etrating and  radiating  from  the  centre  of  the  lobules.    X  45.  (Kolliker.) 


The  hepatic  duct  divides  and  subdivides  in  a  manner  very  like  that  of 
the  portal  vein  and  hepatic  artery,  the  larger  branches  being  lined  by 
cylindrical,  and  the  smaller  by  ^md,]].  polygonal  epithelium. 


272 


HAND-BOOK  OF  PHYSIOLOGY. 


The  bile-capillaries  commence  between  the  hepatic  cells,  and  are 
bounded  by  a  delicate  membranous  wall  of  their  own.  They  appear  to 
be  always  bounded  by  hepatic  cells  on  all  sides,  and  are  thus  separated 

from  the  nearest  blood-capillary  by  at  least  the 
breadth  of  one  cell  (Figs.  203  and  204). 

The  Gail-Bladder.— The  Gall-bladder  (g, 
B,  Fig.  196)  is  a  pyriform  bag,  attached  to  the 
under  surface  of  the  liver,  and  supported  also 
by  the  peritoneum,  which  passes  below  it.  The 
larger  end  or  fundus,  projects  beyond  the 
front  margin  of  the  liver;  while  the  smaller  end 
contracts  into  the  cystic  duct. 

Structure. — The  walls  of  the  gall-bladder 
are  constructed  of  three  principal  coats.  (1) 
Externally  (excepting  that  part  which  is  in 
contact  with  the  liver),  is  the  serous  coat, 
which  has  the  same  structure  as  the  peritoneum 
with  which  it  is  continuous.  Within  this  is 
(2)  the  fibrous  or  areolar  coat,  constructed  of 
tough  fibrous  and  elastic  tissue,  with  which  is 
mingled  a  considerable  number  of  plain  muscu- 
lar fibres,  both  longitudinal  and  circular.  (3)  .Internally  the  gall-bladder 
is  lined  by  mucous  membrane,  and  a  layer  of  columnar  epithelium.  The 
surface  of  the  mucous  membrane  presents  to  the  naked  eye  a  minutely 
honeycombed  appearance  from  a  number  of  tiny  polygonal  depressions 
with  intervening  ridges,  by  which  its  surface  is  mapped  out.    In  the  cystic 


Fig.  203.— Portion  of  a  lobule  of 
liyer.  o,  bile  capillaries  between 
liver-cells,  the  network  in  which 
is  weU  seen;  6,  blood  capillaries. 
X  350.   (Klein  and  Noble  Smith.) 


Fig.  204.— Hepatic  cells  and  bile  capillaries,  from  the  liver  of  a  child  three  months  old.  Both  fig- 
ures i-cjiresent  fraf^iuciits  of  a  section  carried  throufih  the  periphery  of  a  lobule.  The  red  corpuscles 
of  the  blood  aic  rcc-oKiii/.cd  by  their  circular  c-ontom-;  vp,  corresponds  to  an  interlobular  vein  in  im- 
mediate proximity  with  which  are  the  epithelial  cells  of  I  lie  biliary  ducts,  to  which,  at  the  lower  v>art 
of  the  figures,  the  nmch  larger  hepatic  cells  suddenly  succeed.    (,E.  Hering.) 

duct  the  mucous  membrane  is  raised  up  in  the  form  of  crescentic  folds, 
which  together  appear  like  a  spiral  valve,  and  which  minister  to  tho 
function  of  tho  gall-bladder  in  retaining  the  bile  during  the  intervals  of 
digestion. 


DIGESTION. 


273 


The  gall-bladder  and  all  the  main  biliary  ducts  are  provided "  with 
mucous  glands,  which  open  on  their  internal  surface. 

Functions  of  the  Liver. — The  functions  of  the  Liver  may  be 
classified  under  the  following  heads: — 1.  The  Secretion  of  Bile.  2.  The 
Elaboration  of  Blood;  under  this  head  may  be  included  the  Glycogenic 
Function. 

1.  The  Secretioj^"  of  Bile. 

Properties  of  the  Bile. — The  bile  is  a  somewhat  viscid  fluid,  of  a 
yellow  or  reddish-yellow  color,  a  strongly  bitter  taste,  and,  when  fresh, 
with  a  scarcely  perceptible  odor:  it  has  a  neutral  or  slightly  alkaline  reac- 
tion, and  its  specific  gravity  is  about  1020.  Its  color  and  degree  of  con- 
sistence vary  much,  apparently  independent  of  disease;  but,  as  a  rule,  it 
becomes  gradually  more  deeply  colored  and  thicker  as  it  advances  along 
its  ducts,  or  when  it  remains  long  in  the  gall-bladder,  wherein,  at  the 
same  time,  it  becomes  more  viscid  and  ropy,  of  a  darker  color,  and  more 
bitter  taste,  mainly  from  its  greater  degree  of  concentration,  on  account 
of  partial  absorption  of  its  water,  but  partly  also  from  being  mixed  with 
mucus. 


Chemical  Composition  of  Human  Bile.  (Frerichs.) 

Water   859-2 

Solids  140-8 

1000-0 

Bile  salts  or  Bilin  .91*5 

Fat  9-2 

Cholesterin  2.6 

Mucus  and  coloring  matters  29.8 

Salts  7-7 

140-8 

Bile  salts,  or  Bilin,  can  be  obtained  as  colorless,  exceedingly  deliques- 
cent crystals,  soluble  in  water,  alcohol,  and  alkaline  solutions,  giving  to 
the  watery  solution  the  taste  and  general  characters  of  bile.  They  consist 
of  sodium  salts  of  glycocholic  and  taurocholic  acids.  The  former  salt  is 
composed  of  cholic  acid  conjugated  with  glycin  (see  Appendix),  the  latter 
of  the  same  acid  conjugated  with  taurin.  The  proportion  of  these  two 
salts  in  the  bile  of  different  animals  varies,  e.g.,  in  ox  bile  the  glycocho- 
late  is  in  great  excess,  whereas  the  bile  of  the  dog,  cat,  bear,  and  other 
carnivora  contains  taurocholate  alone;  in  human  bile  both  are  present  in 
about  the  same  amount  (glycocholate  in  excess?). 

Preparation  of  Bile  Salt.— Bile  salts  may  be  prepared  in  the  fol- 
VoL.  I.— 18. 


274 


HAND-BOOK  OF  PHYSIOLOGY. 


lowing  manner:  mix  bile  which  has  been  evaporated  to  a  quarter  of  its 
bulk  with  animal  charcoal,  and  evaporate  to  perfect  drj-ness  in  a  water 
bath.  Next  extract  the  mass  whilst  still  warm  with  absolute  alcohol. 
Separate  the  alcoholic  extract  by  filtration,  and  to  it  add  perfectly  anhy- 
drous ether  as  long  as  a  precipitate  is  thrown  down.  The  solution  and 
precipitate  should  be  set  aside  in  a  closely  stoppered  bottle  for  some  days, 
when  crystals  of  the  bile  salts  or  bilin  will  have  separated  out.  The  giy- 
cocholate  may  be  separated  from  the  taurocholate  by  dissolving  bilin  in 
water,  and  adding  to  it  a  solution  of  neutral  lead  acetate,  and  then  a  little 
basic  lead  acetate,  when  lead  glycocholate  separates  out.  Filter  and  add 
to  the  filtrate  lead  acetate  and  ammonia,  a  precipitate  of  lead  taurocho- 
late will  be  formed,  which  may  be  filtered  off.  In  both  cases,  the  lead 
may  be  got  rid  of  by  suspending  or  dissolving  in  hot  alcohol,  adding 
hydrogen  sulphate,  filtering  and  allowing  the  acids  to  separate  out  by  the 
addition  of  water. 

The  test  for  bile  salts  is  known  as  Pettenkofer's.  If  to  an  aqueous 
solution  of  the  salts  strong  sulphuric  acid  be  added,  the  bile  acids  are  first 
of  all  precipitated,  but  on  the  further  addition  of  the  acid  are  re-dissolved. 
If  to  the  solution  a  drop  of  solution  of  cane  sugar  be  added,  a  fine  purple 
color  is  developed. 

The  re-action  will  also  occur  on  the  addition  of  grape  or  fruit  sugar 
instead  of  cane  sugar,  slowly  with  the  first,  quickly  with  the  last;  and  a 
color  similar  to  the  above  is  produced  by  the  action  of  sulphuric  acid  and 
sugar  on  albumen,  the  crystalline  lens,  nerve  tissue,  oleic  acid,  pure  ether, 
cholesterin,  morphia,  codeia  and  amylic  alcohol. 

The  spectrum  of  Pettenkofer's  reaction,  when  the  fluid  is  moderately 
diluted,  shows  four  bands — the  most  marked  and  largest  at  E,  and  a  little 
to  the  left;  another  at  F;  a  third  between  D  and  E,  nearer  to  D;  and 
the  fourth  near  D. 

The  yellow  coloring  matter  of  the  bile  of  man  and  the  Carnivora  is 
termed  BiliruMn  or  Bilifulvin  (CjgHjgj^^Og)  crystallizable  and  insoluble  in 
Avater,  soluble  in  chloroform  or  carbon  disulphate;  a  green  coloring  matter, 
Biliverdin  (Cj^h^qX^oJ,  which  always  exists  in  large  amount  in  the  bile  of 
Herbivora,  being  formed  from  bilirubin  on  exposure  to  the  air,  or  by  sub- 
jecting the  bile  to  any  other  oxidizing  agency,  as  by  adding  nitric  acid. 
When  the  bile  has  been  long  in  the  gall-bladder,  a  third  pigment,  Bih'jrra- 
sin,  may  be  also  found  in  small  amount. 

In  cases  of  biliary  obstruction,  the  coloring  matter  of  the  bile  is  re- 
absorbed, and  circulates  with  the  blood,  giving  to  the  tissues  the  yellow 
tint  characteristic  of  jaundice. 

'i'he  coloring  matters  of  human  bile  do  not  appear  to  give  characteristic 
absorption  spectra;  but  the  bile  of  the  guinea  pig,  rabbit,  mouse,  sheep, 
ox,  and  crow  do  so,  the  most  constant  of  which  appears  to  be  a  band  at 


DIGESTIOIT. 


275 


F.  The  bile  of  the  sheep  and  ox  give  three  bands  in  a  thick  layer,  and 
four  or  five  bands  with  a  thinner  layer,  one  on  each  side  of  D,  one  near 
E,  and  a  faint  line  at  F.  (McMunn.) 

There  seems  to  be  a  close  relationship  between  the  color-matter  of  the 
blood  and  of  the  bile,  and  it  may  be  added,  between  these  and  that  of  the 
urine  (urobilin),  and  of  the  faeces  (stercobilin)  also;  it  is  probable  they 
are,  all  of  them,  varieties  of  the  same  pigment,  or  derived  from  the  same 
source.  Indeed  it  is  maintained  that  UroUUn  is  identical  with  Hydro- 
UliruUn,  a  substance  which  is  obtained  from  bilirubin  by  the  action  of 
sodium  amalgam,  or  by  the  action  of  sodium  amalgam  on  alkaline  hsema- 
tin;  both  urobilin  and  hydrobilirubin  giving  a  characteristic  absorption 
band  between  b  and  F.  They  are  also  identical  with  stercobilin,  which 
is  formed  in  the  alimentary  canal  from  bile  pigments. 

A  common  test  (Gmelin's)  for  the  presence  of  bile-pigment  consists  of 
the  addition  of  a  small  quantity  of  nitric  acid,  yellow  with  nitrous  acid; 
if  bile  be  present,  a  play  of  colors  is  produced,  beginning  with  green  and 
passing  through  blue  and  violet  to  red,  and  lastly  to  yellow.  The  spec- 
trum of  Gmelin's  test  gives  a  black  ^5and 
extending  from  near  b  to  beyond  F. 

Fatty  substances  are  found  in  variable 
proportions  in  the  bile.  Besides  the  ordinary 
saponifiable  fats,  there  is  a  small  quantity 
of  Cholesterin,  a  so-called  non-saponifiable 
fat,  which,  with  the  other  free  fats,  is  prob- 
ably held  in  solution  by  the  bile  salts.  It 
is  a  body  belonging  to  the  class  of  mon- 
atomic  alcohols  (c^eH^^o),  and  crystallizes  in 
rhombic  plates  (Fig.  205).  It  is  insoluble  in 
water  and  cold  alcohol,  but  dissolves  easily  ^^^--^gSterin^ 
in  boiling  alcohol  or  ether.    It  gives  a  red 

color  with  strong  sulphuric  acid,  and  with  nitric  acid  and  ammonia;  also 
a  play  of  colors  beginning  with  blood  red  and  ending  with  green  on 
the  addition  of  sulphuric  acid  and  chloroform.  Lecitliin  (c^^HgoNPOj, 
a  phosphorus-containing  body  and  Neurin  (c^Hj^koJ,  are  also  found  in 
bile,  the  latter  probably  as  a  decomposition  product  of  the  former. 

The  Mucus  in  bile  is  derived  from  the  mucous  membrane  and  glands 
of  the  gall-bladder,  and  of  the  hepatic  ducts.  It  constitutes  the  residue 
after  bile  is  treated  with  alcohol.  The  epithelium  with  which  it  is  mixed 
may  be  detected  in  the  bile  with  the  microscope  in  the  form  of  cylindrical 
cells,  either  scattered  or  still  held  together  in  layers.  To  the  presence  of 
the  mucus  is  probably  to  be  ascribed  the  rapid  decomposition  undergone 
by  the  bilin;  for,  according  to  Berzelius,  if  the  mucus  be  separated,  bile 
w\\\  remain  unchanged  for  many  days. 

The  Saline  or  inorganic  constituents  of  the  bile  are  similar  to  those 


276 


HAND-BOOK  OF  PHYSIOLOGY. 


found  in  most  other  secreted  fluids.  It  is  possible  that  the  carbonate  and 
neutral  phosphate  of  sodium  and  potassium,  found  in  the  ashes  of  bile, 
are  formed  in  the  incineration,  and  do  not  exist  as  such  in  the  fluid. 
Oxide  of  iron  is  said  to  be  a  common  constituent  of  the  ashes  of  bile,  and 
copper  is  generally  found  in  healthy  bile,  and  constantly  in  biliary  calculi. 

Gas — A  certain  small  amount  of  carbonic  acid,  oxygen,  and  nitrogen, 
may  be  extracted  from  bile. 

Mode  of  Secretion  and  Discharge. — The  process  of  secreting  bile 
is  continually  going  on,  but  appears  to  be  retarded  during  fasting,  and 
accelerated  on  taking  food.  This  has  been  shown  by  tying  the  common 
bile-duct  of  a  dog,  and  establishing  a  fistulous  opening  between  the  skin 
and  gall-bladder,  whereby  all  the  bile  secreted  was  discharged  at  the  sur- 
face. It  was  noticed  that  when  the  animal  was  fasting,  sometimes  not  a 
drop  of  bile  was  discharged  for  several  hours;  but  that,  in  about  ten  min- 
utes after  the  introduction  of  food  into  the  stomach,  the  bile  began  to- 
flow  abundantly,  and  continued  to  do  so  during  the  whole  period  of  diges- 
tion.   (Blondlot,  Bidder  and  Schmidt.) 

The  bile  is  formed  in  the  hepatic  cells;  then,  being  discharged  into- 
the  minute  hepatic  ducts,  it  passes  into  the  larger  trunks,  and  from  the 
main  hepatic  duct  may  be  carried  at  once  into  the  duodenum.  But,  prob- 
ably, this  happens  only  while  digestion  is  going  on;  during  fasting,  it 
regurgitates  from  the  common  bile-duct  through  the  cystic  duct,  into  the 
gall-bladder,  where  it  accumulates  till,  in  the  next  period  of  digestion,  it 
is  discharged  into  the  intestine.  The  gall-bladder  thus  fulfils  what  ap- 
pears to  be  its  chief  or  only  office,  that  of  a  reservoir;  for  its  presence 
enables  bile  to  be  constantly  secreted,  yet  insures  its  employment  in  the 
service  of  digestion,  although  digestion  is  periodic,  and  the  secretion  of 
bile  constant. 

The  mechanism  by  which  the  bile  passes  into  the  gall-bladder  is  sim- 
ple. The  orifice  through  which  the  common  bile-duct  communicates 
with  the  duodenum  is  narrower  than  the  duct,  and  appears  to  be  closed, 
except  when  there  is  sufficient  pressure  behind  to  force  the  bile  through 
it.  The  pressure  exercised  upon  the  bile  secreted  during  the  intervals  of 
digestion  appears  insufficient  to  overcome  the  force  with  which  the  ori- 
fice of  the  duct  is  closed;  and  the  bile  in  the  common  duct,  finding  no 
exit  in  the  intestine,  traverses  the  cystic  duct,  and  so  passes  into  the  gall- 
bladder, being  probably  aided  in  this  retrograde  course  by  the  peristaltia 
action  of  the  ducts.  The  bile  is  discharged  from  the  gall-bladder  and 
enters  the  duodenum  on  the  introduction  of  food  into  the  small  intestine: 
being  pressed  on  by  the  contraction  of  the  coats  of  the  gall-bladder,  and 
of  the  common  bile-duct  also;  for  both  these  organs  contain  unstriped 
muscular  fibre-cells.  Their  contraction  is  excited  by  the  stimulus  of  the 
food  in  the  duodenum  acting  so  as  to  produce  a  reflex  movement,  the  force 
of  which  is  sufficient  to  open  the  orifice  of  the  common  bile-duct. 


DIGESTION. 


277 


Bile,  as  such,  is  not  pre-formed  in  the  blood.  As  just  observed,  it  is 
formed  by  the  hepatic  cells,  although  some  of  the  material  may  be  brought 
to  them  almost  in  the  condition  for  immediate  secretion.  When  it  is, 
however,  prevented  by  an  obstruction  of  some  kind,  from  escaping  into 
the  intestine  (as  by  the  passage  of  a  gall-stone  along  the  hepatic  duct)  it 
is  absorbed  in  great  excess  into  the  blood,  and,  circulating  with  it,  gives 
rise  to  the  well-known  phenomena  of  jaundice.  This  is  explained  by  the 
fact  that  the  pressure  of  secretion  in  the  ducts  is  normally  very  low,  and 
if  it  exceeds  f  inch  of  mercury  (16  mm.)  the  secretion  ceases  to  be  poured 
out,  and  if  the  opposing  force  be  increased,  the  bile  finds  its  way  into 
the  blood. 

Quantity. — Various  estimates  have  been  made  of  the  quantity  of  bile 
discharged  into  the  intestines  in  twenty-four  hours:  the  quantity  doubtless 
varying,  like  that  of  the  gastric  fluid,  in  proportion  to  the  amount  of 
food  taken.  A  fair  average  of  several  computations  would  give  20  to 
40  oz.  (600 — 900  cc.)  as  the  quantity  daily  secreted  by  man. 

Uses. — (1)  As  an  excrementitious  substance,  the  bile  may  serve 
especially  as  a  medium  for  the  separation  of  excess  of  carbon  and  hydrogen 
from  the  blood;  and  its  adaptation  to  this  purpose  is  well  illustrated  by 
the  peculiarities  attending  its  secretion  and  disposal  in  the  foetus.  During 
intra-uterine  life,  the  lungs  and  the  intestinal  canal  are  almost  inactive; 
there  is  no  respiration  of  open  air  or  digestion  of  food;  these  are  unneces- 
sary, on  account  of  the  supply  of  well  elaborated  nutriment  received  by 
the  vessels  of  the  foetus  at  the  placenta.  The  liver,  during  the  same  time, 
is  proportionately  larger  than  it  is  after  birth,  and  the  secretion  of  bile  is 
active,  although  there  is  no  food  in  the  intestinal  canal  upon  which  it 
can  exercise  any  digestive  property.  At  birth,  the  intestinal  canal  is  full 
of  thick  bile,  mixed  with  intestinal  secretion;  the  meconium,  or  fasces  of 
the  foetus,  containing  all  the  essential  principles  of  bile. 

Composition  of  Meconium  (Frerichs) : 

Biliary  resin  15.6 

Common  fat  and  cholesterin  .  .  .  ,15.4 
Epithelium,  mucus,  pigment,  and  salts   .  .69.0 

100.0 

In  the  foetus,  therefore,  the  main  purpose  of  the  secretion  of  bile  must  be 
the  purification  of  blood  by  direct  excretion,  i.e.,  by  separation  from  the 
blood,  and  ejection  from  the  body  without  further  change.  Probably  all 
the  bile  secreted  in  foetal  life  is  incorporated  in  the  meconium,  and  with 
it  discharged,  and  thus  the  liver  may  be  said  to  discharge  a  function  in 
some  sense  vicarious  of  that  of  the  lungs.  For,  in  the  foetus,  nearly  all 
the  blood  coming  from  the  placenta  passes  through  the  liver,  previous  to 
its  distribution  to  the  several  organs  of  the  body;  and  the  abstraction  of 


278 


HAND-BOOK  OF  PHYSIOLOGY. 


carbon,  hydrogen,  and  other  elements  of  bile  will  purify  it,  as  in  extra- 
uterine life  it  is  purified  by  the  separation  of  carbonic  acid  and  water  at 
the  Inngs. 

The  evident  disposal  of  the  foetal  bile  by  excretion,  makes  it  highly 
probable  that  the  bile  in  extra-uterine  life  is  also,  at  least  in  part,  destined 
to  be  discharged  as  excrementitious.  The  analysis  of  the  faeces  of  both 
children  and  adults  shows  that  (except  when  rapidly  discharged  in  pur- 
gation) they  contain  very  little  of  the  bile  secreted,  probably  not  more 
than  one-sixteenth  part  of  its  weight,  and  that  this  portion  includes 
chiefly  its  coloring,  and  some  of  its  fatty  matters,  and  to  only  a  very* 
sliglit  degree,  its  salts,  almost  all  of  which  have  been  re-absorbed  from 
the  intestines  into  the  blood. 

The  elementary  composition  of  bile  salts  shows,  however,  such  a  pre- 
ponderance of  carbon  and  hydrogen,  that  probably,  after  absorption,  it 
combines  with  oxygen,  and  is  excreted  in  the  form  of  carbonic  acid  and 
water.  The  change  after  birth,  from  the  direct  to  the  indirect  mode  of 
excretion  of  the  bile,  may,  with  much  probability,  be  connected  with  a 
purpose  in  relation  to  the  development  of  heat.  The  temperature  of  the 
foetus  is  maintained  by  that  of  the  parent,  and  needs  no  source  of  heat 
within  itself;  but,  in  extra-uterine  life,  there  is  (as  one  may  say)  a  waste 
of  material  for  heat  when  any  excretion  is  discharged  unoxidized;  the 
carbon  and  hydrogen  of  the  bilin,  therefore,  instead  of  being  ejected  in 
the  faeces,  are  re-absorbed,  in  order  that  they  may  be  combined  with 
oxygen,  and  that  in  the  combination  heat  may  be  generated. 

A  substance,  which  has  been  discovered  in  the  faeces,  and  named  ster- 
corin  is  closely  allied  to  cholesterin;  and  it  has  been  suggested  that  while 
one  great  function  of  the  liver  is  to  excrete  cholesterin  from  the  blood,  as 
the  kidney  excretes  urea,  the  stercorin  of  f^ces  is  the  modified  form  in 
which  cholesterin  finally  leaves  the  body.  Ten  grains  and  a  half  of  ster- 
corin are  excreted  daily  (A.  Flint). 

From  the  peculiar  manner  in  which  the  liver  is  supplied  with  much 
of  the  blood  that  flows  through  it,  it  is  probable  that  this  organ  is  excre- 
tory, not  only  for  such  hydro-carbonaceous  matters  as  may  need  expulsion 
from  any  portion  of  the  blood,  but  that  it  serves  for  the  direct  purification 
of  the  stream  which,  arriving  by  the  portal  vein,  has  just  gathered  up 
various  substances  in  its  course  through  the  digestive  organs — substances 
which  may  need  to  be  expelled,  almost  immediately  after  their  absorption. 
For  it  is.  easily  conceivable  that  many  things  may  be  taken  up  during 
digestion,  which  not  only  are  unfit  for  purposes  of  nutrition,  but  which 
would  be  positively  injurious  if  allowed  to  mingle  with  the  general  mass 
of  the  blood.  The  liver,  therefore,  may  be  supposed  placed  in  the  only 
road  by  which  such  matters  can  pass  unchanged  into  the  general  current, 
jealously  to  guard  against  their  further  i)rogress,  and  turn  them  back 
again  into  an  excretory  channel.    The  frequency  with  which  metallic 


DIGESTIOJS^. 


279 


poisons  are  either  excreted  by  the  liver,  or  intercepted  and  retained,  often 
for  a  considerable  time,  in  its  own  substance,  may  be  adduced  as  evidence 
for  the  probable  truth  of  this  supposition. 

(2).  As  a  digestive  fluid. — Though  one  chief  purpose  of  the  secretion 
of  bile  may  thus  appear  to  be  the  purification  of  the  blood  by  ultimate 
excretion,  yet  thgre  are  many  reasons  for  believing  that,  while  it  is  in  the 
intestines,  it  performs  an  important  part  in  the  process  of  digestion.  In 
nearly  all  animals,  for  example,  the  bile  is  discharged,  not  through  an 
excretory  duct  communicating  with  the  external  surface  or  with  a  simple 
reservoir,  as  most  excretions  are,  but  is  made  to  pass  into  the  intestinal 
canal,  so  as  to  be  mingled  with  the  chyme  directly  after  it  leaves  the 
stomach;  an  arrangement,  the  constancy  of  which  clearly  indicates  that 
the  bile  has  some  important  relations  to  the  food  with  which  it  is  thus 
mixed.  A  similar  indication  is  furnished  also  by  the  fact  that  the  secre- 
tion of  bile  is  most  active,  and  the  quantity  discharged  into  the  intestines 
much  greater,  during  digestion  than  at  any  other  time;  although,  with- 
out doubt,  this  activity  of  secretion  during  digestion  may,  however,  be 
in  part  ascribed  to  the  fact  that  a  greater  quantity  of  blood  is  sent  through 
the  portal  vein  to  the  liver  at  this  time,  and  that  this  blood  contains  some 
of  the  materials  of  the  food  absorbed  from  the  stomach  and  intestines, 
which  may  need  to  be  excreted,  either  temporarily  (to  be  afterward  reab- 
sorbed) or  permanently. 

Eespecting  the  functions  discharged  by  the  bile  in  digestion  there  is 
little  doubt  that  it,  (a.)  assists  in  emulsifying  the  fatty  portions  of  the 
food,  and  thus  rendering  them  capable  of  being  absorbed  by  the  lacteals. 
For  it  has  appeared  in  some  experiments  in  which  the  common  bile-duct 
was  tied,  that,  although  the  process  of  digestion  in  the  stomach  was  un- 
affected, chyle  was  no  longer  well  formed;  the  contents  of  the  lacteals 
consisting  of  clear,  colorless  fluid,  instead  of  being  opaque  and  white,  as 
they  ordinarily  are,  after  feeding. 

{b.)  It  is  probable,  also,  that  the  moistening  of  the  mucous  memhrane 
of  the  intestines  by  bile  facilitates  absorption  of  fatty  matters  through  it. 

{c.)  The  bile,  like  the  gastric  fluid,  has  a  considerable  antiseptic 
power,  and  may  serve  to  prevent  the  decomposition  of  food  during  the 
time  of  its  sojourn  in  the  intestines.  Experiments  show  that  the  con- 
tents of  the  intestines  are  much  more  foetid  after  the  common  bile-duct 
has  been  tied  than  at  other  times;  moreover,  it  is  found  that  the  mixture 
of  bile  with  a  fermenting  fluid  stops  or  spoils  the  process  of  fermentation. 

{d.)  The  bile  has  also  been  considered  to  act  as  a  natural  purgative, 
by  promoting  an  increased  secretion  of  the  intestinal  glands,  and  by 
stimulating  the  intestines  to  the  propulsion  of  their  contents.  This  view 
receives  support  from  the  constipation  which  ordinarily  exists  in  jaundice, 
from  the  diarrhoea  which  accompanies  excessive  secretion  of  bile,  and  from 
the  purgative  properties  of  ox-gall. 


280 


HAND-BOOK  OF  PHYSIOLOGY. 


(e.)  The  bile  appears  to  have  the  power  of  2^'>^ecipitating  the  gastric 
parapeptones  and  peptones,  together  ^uith  the  pepsin  which  is  mixed  up 
with  them,  as  soon  as  the  contents  of  the  stomach  meet  it  in  the  duo- 
denum. The  purpose  of  this  operation  is  probably  both  to  delay  any 
change  in  the  parapeptones  until  the  pancreatic  juice  can  act  upon  them, 
and  also  to  prevent  the  pepsin  from  exercising  its  solvent  action  on  the 
ferments  of  the  pancreatic  juice.  • 

Nothing  is  known  with  certainty  respecting  the  changes  which  the  re- 
absorbed portions  of  the  bile  undergo.  That  they  are  much  changed 
appears  from  the  impossibility  of  detecting  them  in  the  blood;  and  that 
part  of  this  change  is  effected  in  the  liver  is  probable  from  an  experiment 
of  Magendie,  who  found  that  when  he  injected  bile  into  the  portal  vein, 
a  dog  was  unharmed,  but  was  killed  when  he  injected  the  bile  into  one  of 
the  systemic  vessels. 

II.  The  Liter  as  a  BLOOD-ELABOKATiis-G  Gla^s"©. 

The  secretion  of  bile,  as  already  observed,  is  only  one  of  the  purposes 
fulfilled  by  the  liver.  Another  very  important  function  appears  to  be 
that  of  so  acting  upon  certain  constituents  of  the  blood  passing  through 
it,  as  to  render  some  of  them  capable  of  assimilation  with  the  blood  gen- 
erally, and  to  prepare  others  for  being  duly  eliminated  in  the  process  of 
respiration.  It  appears  that  the  peptones,  conveyed  from  the  alimentary 
canal  by  the  blood  of  the  portal  vein,  require  to  be  submitted  to  the  influ- 
ence of  the  liver  before  they  can  be  assimilated  by  the  blood;  for  if  such 
albumi]ious  matter  is  injected  into  the  jugular  vein,  it  speedily  appears  in 
the  urine;  but  if  introduced  into  the  portal  vein,  and  thus  allowed  to 
traverse  the  liver,  it  is  no  longer  ejected  as  a  foreign  substance,  but  is 
incorporated  with  the  albuminous  pai-t  of  the  blood.  Albuminous  mat- 
ters are  also  subject  to  decomposition  by  the  liver  in  another  way  to  be 
immediately  noticed  (p.  281).  The  formation  of  urea  by  the  liver  will  be 
again  referred  to  (p.  371). 

Glycogenic  Function. — One  of  the  chief  uses  of  the  liver  in  connec- 
tion with  elaboration  of  the  blood  is  comprised  in  what  is  known  as  its 
glycogenic  function.  The  important  fact  that  the  liver  normally  forms 
glucose  or  grape  sugar,  or  a  substance  readily  convertible  into  it,  was  dis- 
covered by  Claude  Bernard  in  the  course  of  some  experiments  which  he 
undertook  for  the  purpose  of  finding  out  in  what  part  of  the  circulatory 
system  the  saccharine  matter  disappeared,  which  was  absorbed  from  the 
alimentary  canal.  With  this  purpose  he  fed  a  dog  for  seven  days  with 
food  containing  a  large  quantity  of  sugar  and  starch;  and,  as  might  be 
expect  found  sugar  in  both  the  portal  and  hepatic  veins.  He  then 
fed  :i  (log  with  meat  only,  and,  to  his  surprise,  still  found  sugar  in  the 


DIGESTION. 


281 


hepatic  veins.  Eepeated  experiments  gave  invariably  the  same  result;  no 
sugar  being  found,  under  a  meat  diet,  in  the  portal  vein,  if  care  were 
taken,  by  applying  a  ligature  on  it  at  the  transverse  fissure,  to  prevent 
reflux  of  blood  from  the  hepatic  venous  system.  Bernard  found  sugar 
also  in  the  substance  of  the  liver.  It  thus  seemed  certain  that  the  liver 
formed  sugar,  even  when,  from  the  absence  of  saccharine  and  amyloid 
matters  in  the  food,  none  could  be  brought  directly  to  it  from  the  stomach 
or  intestines. 

Excepting  cases  in  which  large  quantities  of  starch  and  sugar  were 
taken  as  food,  no  sugar  was  found  in  the  blood  after  it  had  passed  through 
the  lungs;  the  sugar  formed  by  the  liver,  having  presumably  disa^^peared 
by  combustion,  in  the  course  of  the  pulmonary  circulation. 

Bernard  found,  subsequently  to  the  before-mentioned  experiments, 
that  a  liver,  removed  from  the  body,  and  from  which  all  sugar  had  been 
completely  washed  away  by  injecting  a  stream  of  water  through  its  blood- 
vessels, will  be  found,  after  the  lapse  of  a  few  hours,  to  contain  sugar  in 
abundance.  This  post-mortem  production  of  sugar  was  a  fact  which  could 
only  be  explained  in  the  supposition  that  the  liver  contained  a  substance, 
readily  convertible  into  sugar  in  the  course  merely  of  post-mortem  decom- 
position; and  this  theory  was  proved  correct  by  the  discovery  of  a  sub- 
stance in  the  liver  allied  to  starch,  and  now  generally  termed  glycogen. 
We  may  believe,  therefore,  that  the  liver  does  not  form  sugar  directly 
from  the  materials  brought  to  it  by  the  blood,  but  that  glycogen  is  first 
formed  and  stored  in  its  substance;  and  that  the  sugar,  when  present,  is 
the  result  of  the  transformation  of  the  latter. 

Quantity  of  Glycogen  formed. — Although,  as  before  mentioned,  glyco- 
gen is  produced  by  the  liver  when  neither  starch  nor  sugar  is  present  in 
the  food,  its  amount  is  much  less  under  such  a  diet. 

Average  amount  of  Glycogen  in  the  Liver  of  Dogs  tinder  various  Diets. 

(Pavy.) 

Diet.  .  Amount  of  Glycogen  in  Liver. 

Animal  food  7*19  per  cent. 

Animal  food  with  sugar  (about  \  lb.  of  sugar  daily)  14*5 
Vegetable  diet  (potatoes,  with  bread  or  barley-meal)  17-23 

The  dependence  of  the  formation  of  glycogen  on  the  food  taken  is  also 
well  shown  by  the  following  results,  obtained  by  the  same  experimenter: 

Average  quantity  of  Glycogen  found  in  the  Liver  of  RaMits  after  Fasting 
and  after  a  diet  of  Starch  and  Sugar  respectively. 

Average  amount  of  Glycogen  in  Liver. 
After  fasting  for  three  days       ....  Practically  absent. 
"    diet  of  starch  and  grape-sugar  .       .       .15*4  per  cent. 
"       "      cane-sugar  16-9  " 


282 


HAND-BOOK  OF  PHYSIOLOGY. 


Regardiug  these  facts  there  is  no  dispute.  .  All  are  agreed  that  glyco- 
gen is  formed,  and  laid  up  in  store,  temporarily,  by  the  liver-cells;  and 
that  it  is  not  formed  exclusively  from  saccharine  and  amylaceous  foods, 
but  from  albuminous  substances  also;  the  albumen,  in  the  latter  case, 
being  probably  split  up  into  glycogen,  which  is  temporarily  stored  in  the 
liver,  and  urea,  which  is  excreted  by  the  kidneys. 

Destination  of  Glycogen. — There  are  two  chief  theories  on  the  sub- 
ject of  the  destination  of  glycogen.  (1.)  That  the  conversion  of  glycogen 
into  sugar  takes  place  rapidly  during  life  by  the  agency  of  a  ferment  also 
formed  in  the  liver:  and  the  sugar  is  conveyed  away  by  the  blood  of  the 
hepatic  veins,  and  soon  undergoes  combustion.  (2.)  That  the  conver- 
sion into  sugar  only  occurs  after  death,  and  that  during  life  no  sugar 
exists  in  healthy  livers;  glycogen  not  undergoing  this  transformation. 
The  chief  arguments  advanced  in  support  of  this  view  are,  (a)  that 
scarcely  a  trace  of  sugar  is  found  in  blood  drawn  during  life  from  the 
right  ventricle,  or  in  blood  collected  from  the  right  side  of  the  heart  im- 
7necliateJy  after  an  animal  has  been  killed;  while  if  the  examination  be 
delayed  for  a  very  short  time  after  death,  sugar  in  abundance  may  be 
found  in  such  blood;  (&),  that  the  liver,  like  the  venous  blood  in  the 
heart,  is,  at  the  moment  of  death,  completely  free  from  sugar,  although 
afterward  its  tissue  speedily  becomes  saccharine,  unless  the  formation  of 
sugar  be  prevented  by  freezing,  boiling,  or  other  means  calculated  to  in- 
terfere with  the  action  of  a  ferment  on  the  amyloid  substance  of  the 
organ.  Instead  of  adopting  Bernard^s  view,  that  normally,  during  life, 
glycogen  passes  as  sugar  into  the  hepatic  venous  blood,  and  thereby  is 
conveyed  to  the  lungs  to  be  further  disposed  of,  Pavy  inclines  to  the 
belief  that  it  may  represent  an  intermediate  stage  in  the  formation  of  fat 
from  materials  absorbed  from  the  alimentary  canal. 

Liver-sugar  and  Glycogen. — To  demonstrate  the  presence  of  sugar 
in  the  liver,  a  portion  of  this  organ,  after  being  cut  into  small  pieces,  is 
bruised  in  a  mortar  to  a  pulp  with  a  small  quantity  of  water,  and  the 
pulp  is  boiled  with  sodium-sulphate  in  order  to  precipitate  albuminous 
and  coloring  matters.  The  decoction  is  then  filtered  and  may  be  tested 
for  glucose  (p.  230). 

Glycogen  (CgHj^o.)  is  an  amorphous,  starch-like  substance,  odorless  and 
tasteless,  soluble  in  water,  insoluble  in  alcohol.  It  is  converted  into  glu- 
cose by  boiling  with  dilute  acids,  or  by  contact  with  any  animal  ferment. 
It  may  be  obtained  by  taking  a  portion  of  liver  from  a  recently  killed 
rabbit,  and,  after  cutting  it  into  small  pieces,  placing  it  for  a  short  time 
in  boiling  water.  It  is  then  bruised  in  a  mortar,  until  it  forms  a  pulpy 
mass,  and  subsequently  boiled  in  distilled  water  for  about  a  quarter  of  an 
hour.  The  glycogen  is  precipitated  from  the  filtered  decoction  by  the 
addition  of  alcohol.  Glycogen  has  been  found  in  many  other  structures 
than  the  liver.    (See  Ai)pendix.) 


DIGESTION. 


283 


Glycosuria. — The  facility  with  which  the  glycogen  of  the  liver  is 
transformed  into  sugar  would  lead  to  the  expectation  that  this  chemical 
change,  under  many  circumstances,  would  occur  to  such  an  extent  that 
sugar  would  be  present  not  only  in  the  hepatic  veins,  but  in  the  blood 
generally.  Such  is  frequently  the  case;  the  sugar  when  in  excess  in  the 
blood  being  secreted  by  the  kidneys,  and  thus  appearing  in  variable  quan- 
tities in  the  urine  (Glycosuria). 

Influence  of  the  Nervous  System  in  producing  Glycosuria. — 
Glycosuria  may  be  experimentally  produced  by  puncture  of  the  medulla 
oblongata  in  the  region  of  the  vaso-motor  centre.  The  better  fed  the 
animal  the  larger  is  the  amount  of  sugar  found  in  the  urine;  whereas  in 
the  case  of  a  starving  animal  no  sugar  appears.  It  is,  therefore,  highly 
probable  that  the  sugar  comes  from  the  hepatic  glycogen,  since  in  the  one 
case  glycogen  is  in  excess,  and  in  the  other  it  is  almost  absent.  The 
nature  of  the  influence  is  uncertain.  It  may  be  exercised  in  dilating  the 
hepatic  vessels,  or  possibly  on  the  liver  cells  themselves.  The  whole 
course  of  the  nervous  stimulus  cannot  be  traced  to  the  liver,  but  at  first 
it  passes  from  the  medulla  down  the  spinal  cord  as  far  as — in  rabbits — 
the  fourth  dorsal  vertebra,  and  thence  to  the  first  thoracic  ganglion. 

Many  other  circumstances  will  cause  glycosuria.  It  has  been  observed 
after  the  administration  of  various  drugs,  after  the  injection  of  urari, 
poisoning  with  carbonic  oxide  gas,  the  inhalation  of  ether,  chloroform, 
etc.,  the  injection  of  oxygenated  blood  into  the  portal  venous  system.  It 
has  been  observed  in  man  after  injuries  to  the  head,  and  in  the  course  of 
various  diseases. 

The  well-known  disease,  tUahetus  melUtus,  in  which  a  large  quantity 
of  sugar  is  persistently  secreted  daily  with  the  urine,  has,  doubtless,  some 
close  relation  to  the  normal  glycogenic  function  of  the  li\^er;  but  the 
nature  of  the  relationship  is  at  present  quite  unknown. 

The  Intestinal  Secretion,  or  Succus  Entericus. — On  account  of 
the  difiiculty  in  isolating  the  secretion  of  the  glands  in  the  wall  of  the 
intestine  (Brunner^s  and  Lieberkiihn's)  from  other  secretions  poured  into 
the  canal  (gastric  juice,  bile,  and  pancreatic  secretion),  but  little  is  known 
regarding  the  composition  of  the  former  fluid  (intestinal  juice,  succus  en- 
tericus). 

It  is  said  to  be  a  yellowish .  alkaline  fluid  with  a  specific  gravity  of 
1011,  and  to  contain  about  2*5  per  cent,  of  solid  matters  (Thiry). 

Functions. — The  secretion  of  Brunner's  glands  is  said  to  be  able  to 
convert  proteids  into  peptones,  and  that  of  Lieberkiihn^s  is  believed  to 
convert  starch  into  sugar.  To  these  functions  of  the  succus  entericus  the 
powers  of  converting  cane  into  grape  sugar,  and  of  turning  cane  sugar 
into  lactic,  and  afterward  into  butyric  acid,  are  added  by  some 
physiologists.  It  also  probably  contains  a  milk-curdling  ferment  (W. 
Roberts). 


284 


HAND-BOOK  OF  PHYSIOLOGY. 


The  reaction  which  represents  tlie  conversion  of  cane  sugar  into  grape 
sugar  may  be  represented  thus: — 

8C„H„0„   +  2H,0   =   C„H„0.,  +   C„  H,,  0„ 

Saccharose  Water  Dextrose  Laevulose 

The  conversion  is  probably  effected  by  means  of  a  hydrolytic  ferment. 
(Inversive  ferment,  Bernard.) 

The  length  and  complexity  of  the  digestive  tract  seem  to  be  closely 
connected  with  the  character  of  the  food  on  which  an  animal  lives.  Thus, 
in  all  carnivorous  animals,  such  as  the  cat  and  dog,  and  pre-eminently  in 
carnivorous  birds,  as  hawks  and  herons,  it  is  exceedingly  short.  The 
seals,  which,  though  carnivorous,  possess  a  very  long  intestine,  appear  to 
furnish  an  exception;  but  this  is  doubtless  to  be  explained  as  an  adaptation 
to  their  aquatic  habits:  their  constant  exposure  to  cold  requiring  that 
they  should  absorb  as  much  as  possible  from  their  intestines. 

Herbivorous  animals,  on  the  other  hand,  and  the  ruminants  especially, 
have  very  long  intestines  (in  the  sheep  30  times  the  length  of  the  body) 
wiiich  is  no  doubt  to  be  connected  with  their  lowly  nutritious  diet.  In 
others,  such  as  the  rabbit,  though  the  intestines  are  not  excessively  long, 
this  is  compensated  by  the  great  length  and  capacity  of  the  caecum.  In 
man,  the  length  of  the  intestines  is  intermediate  between  the  extremes 
of  the  carnivora  and  herbivora,  and  his  diet  also  is  intermediate. 

Summary  of  the  Digestive  Changes  in  the  Small  Intestine. 

In  order  to  understand  the  changes  in  the  food  which  occur  during 
its  passage  through  the  small  intestine,  it  will  be  well  to  refer  briefly  to 
the  state  in  which  it  leaves  the  stomach  through  the  pylorus.  It  has 
been  said  before,  that  the  chief  office  of  the  stomach  is  not  only  to  mix 
into  a  uniform  mass  all  the  varieties  of  food  that  reach  it  through  the 
oesophagus,  but  especially  to  dissolve  the  nitrogenous  portion  by  means 
of  the  gastric  juice.  The  fatty  matters,  during  their  sojourn  in  the 
stomach,  become  more  thoroughly  mingled  with  the  other  constituents 
of  the  food  taken,  but  are  not  yet  in  a  state  fit  for  absorption.  The  con- 
version of  starch  into  sugar,  which  began  in  the  mouth,  has  been  inter- 
fered with,  if  not  altogether  stopped.  The  soluble  matters — both  those 
which  were  so  from  the  first,  as  sugar  and  saline  matter,  and  the  gastric 
peptones — have  begun  to  disappear  by  absorption  into  the  blood-vessels, 
and  the  same  thing  has  befallen  such  fluids  as  may  have  been  swallowed, 
— wine,  water,  etc. 

The  thin  pultaceous  chyme,  therefore,  which  during  the  whole  period 
of  gastric  digestion,  is  being  constantly  squeezed  or  strained  through  the 
pyloric  orifice  into  the  duodenum,  consists  of  albuminous  matter,  broken 
down,  dissolving  and  half  dissolved;  fatty  matter  broken  down  and 
molted,  but  not  dissolved  at  all;  starch  very  slowly  in  process  of  conversion 
into  sugar,  and  as  it  becomes  sugar,  also  dissolving  in  the  fluids  with  which 


DIGESTION. 


285 


it  IS  mixed;  while,  with  these  are  mingled  gastric  fluid,  and  fluid  that  has 
been  swallowed,  together  with  such  portions  of  the  food  as  are  not  digest- 
ible, and  will  be  finally  expelled  as  part  of  the  faeces. 

On  the  entrance  of  the  chyme  into  the  duodenum,  it  is  subjected  to 
the  influence  of  the  bile  and  pancreatic  juice,  which  are  then  poured  out, 
and  also  to  that  of  the  succus  entericus.  All  these  secretions  have  a  more 
or  less  alkaline  reaction,  and  by  their  admixture  with  the  gastric  chyme 
its  acidity  becomes  less  and  less  until  at  length,  at  about  the  middle  of 
the  small  intestine,  the  reaction  becomes  alkaline  and  continues  so  as  far 
as  the  ileo-csecal  valve. 

The  special  digestive  functions  of  the  small  intestine  may  be  taken  in 
the  following  order: — 

(1.)  One  important  duty  of  the  small  intestine  is  the  alteration  of  the 
fat  in  such  a  manner  as  to  make  it  fit  for  absorption;  and  there  is  no 
doubt  that  this  change  is  chiefly  effected  in  the  upper  part  of  the  small 
intestine.  What  is  the  exact  share  of  the  process,  however,  allotted  re- 
spectively to  the  bile,  to  the  pancreatic  secretion,  and  to  the  intestinal 
juice,  is  still  uncertain, — probably  the  pancreatic  juice  is  the  most  impor- 
tant. The  fat  is  changed  in  two  ways.  {a).  To  a  slight  extent  it  is 
chemically  decomposed  by  the  alkaline  secretions  with  which  it  is  mingled, 
and  a  soap  is  the  result,  {l).  It  is  emulsionized,  i.e.,  its  particles  are 
minutely  subdivided  and  diffused,  so  that  the  mixture  assumes  the  condi- 
tion of  a  milky  fluid,  or  emulsion.  As  will  be  seen  in  the  next  Chapter, 
most  of  the  fat  is  absorbed  by  the  lacteals  of  the  intestine,  but  a  small 
part,  which  is  saponified,  is  also  absorbed  by  the  blood-vessels. 

(2.)  ThQ  albuminous  substances  which  have  been  partly  dissolved  in 
the  stomach,  and  have  not  been  absorbed,  are  subjected  to  the  action  of 
the  pancreatic  and  intestinal  secretions.  The  pepsin  is  rendered  inert 
by  being  precipitated  together  with  the  gastric  peptones  and  parapeptones, 
as  soon  as  the  chyme  meets  with  bile.  By  these  means  the  pancreatic  fer- 
ment trypsin  is  enabled  to  proceed  with  the  further  conversion  of  the 
parapeptones  into  peptones,  and  of  part  of  the  peptones  (hemipeptone, 
Kiihne)  into  leucin  and  tyrosin.  Albuminous  substances,  which  are 
chemically  altered  in  the  process  of  digestion  (peptones),  and  gelatinous 
matters  similarly  changed,  are  absorbed  by  both  the  blood-vessels  and 
lymphatics  of  the  intestinal  mucous  membrane.  Albuminous  matters, 
in  a  state  of  solution,  which  have  not  undergone  the  peptonic  change,  are 
probably,  from  the  difficulty  with  which  they  diffuse,  absorbed,  if  at  all, 
almost  solely  by  the  lymphatics. 

(3.)  The  starchy,  or  amyloid  portions  of  the  food,  the  conversion  of 
which  into  dextrin  and  sugar  was  more  or  less  interrupted  during  its  stay 
in  the  stomach,  is  now  acted  on  briskly  by  the  pancreatic  juice  and  the 
succus  entericus;  and  the  sugar,  as  it  is  formed,  is  dissolved  in  the  intes- 
tinal fluids,  and  is  absorbed  chiefly  by  the  blood-vessels. 


286 


HAND-BOOK  OF  PHYSIOLOGY. 


(4.)  Saline  and  saccharine  matters,  as  common  salt,  or  cane  sugar, 
if  not  in  a  state  of  solution  beforehand  in  the  saliva  or  other  fluids  which 
ma}^  have  been  swallowed  with  them,  are  at  once  dissolved  in  the  stomach, 
and  if  not  here  absorbed,  are  soon  taken  up  in  the  small  intestine;  the 
blood-vessels,  as  in  the  last  case,  being  chiefly  concerned  in  the  absorp- 
tion. Cane  sugar  is  in  part  or  wholly  converted  into  grape-sugar  before 
its  absorption.  This  is  accomplished  partially  in  the  stomach,  but  also 
by  a  ferment  in  the  succus  entericus. 

(5.)  The  liquids,  including  in  this  term  the  ordinary  drinks,  as  water, 
wine,  ale,  tea,  etc.,  which  may  have  escaped  absorption  in  the  stomach, 
are  absorbed  probably  very  soon  after  their  entrance  into  the  intestine; 
the  fluidity  of  the  contents  of  the  latter  being  preserved  more  by  the  con- 
stant secretion  of  fluid  by  the  intestinal  glands,  pancreas,  and  liver,  than 
by  any  given  portion  of  fluid,  whether  swallowed  or  secreted,  remaining 
long  unabsorbed.  From  this  fact,  therefore,  it  may  be  gathered  that 
there  is  a  kind  of  circulation  constantly  proceeding  from  the  intestines 
into  the  blood,  and  from  the  blood  into  the  intestines  again;  for  as  all  the 
fluid — a  very  large  amount — secreted  by  the  intestinal  glands,  must  come 
from  the  blood,  the  latter  would  be  too  much  drained,  were  it  not  that 
the  same  fluid  after  secretion  is  again  re-absorbed  into  the  current  of  blood 
— going  into  the  blood  charged  with  nutrient  products  of  digestion — com- 
ing out  again  by  secretion  through  the  glands  in  a  comparatively  un- 
charged condition. 

At  the  lower  end  of  the  small  intestine,  the  chyme,  still  thin  and  pul- 
taceous,  is  of  a  light  yellow  color,  and  has -a  distinctly  faecal  odor.  This 
odor  depends  upon  the  formation  of  indol.  In  this  state  it  passes  through 
the  ileo-csecal  opening  into  the  large  intestine. 

SUMMAKY  OF  THE  DIGESTIVE  CHANGES  11^"  THE  LaKGE  IkTESTII^E. 

The  changes  which  take  place  in  the  chyme  in  the  large  intestine  are 
probably  only  the  continuation  of  the  same  changes  that  occur  in  the 
course  of  the  food's  passage  through  the  upper  part  of  the  intestinal  canal. 
From  the  absence  of  villi,  however,  we  may  conclude  that  absorption, 
especially  of  fatty  matter,  is  in  great  part  completed  in  the  small  intes- 
tine; while,  from  the  still  half -liquid,  pultaceous  consistence  of  the  chyme 
when  it  first  enters  the  caecum,  there  can  be  no  doubt  that  the  absorption 
of  liquid  is  not  by  any  means  concluded.  The  peculiar  odor,  moreover, 
which  is  acquired  after  a  short  time  by  the  contents  of  the  large  bowel, 
would  seem  to  indicate  a  further  chemical  change  in  the  alimentary  mat- 
ters or  in  the  digestive  fluids,  or  both.  The  acid  reaction,  which  had  dis- 
appeared in  tlie  small  bowel,  again  becomes  very  manifest  in  the  caecum 
— probably  from  acid  fermentation-processes  in  some  of  the  materials  of 
the  food. 


DIGESTION. 


287 


There  seems  no  reason  to  conclude  that  any  special  "secondary  diges- 
tive" process  occurs  in  the  caecum  or  in  any  other  part  of  the  large  intestine. 
Probably  any  constituent  of  the  food  which  has  escaped  digestion  and 
absorption  in  the  small  bowel  may  be  digested  in  the  large  intestine;  and 
the  power  of  this  part  of  the  intestinal  canal  to  digest  fatty,  albuminous, 
or  other  matters,  may  be  gathered  from  the  good  effects  of  nutrient  ene- 
mata,  so  frequently  given  when  from  any  cause  there  is  difficulty  in  intro- 
ducing food  into  the  stomach.  In  ordinary  healthy  digestion,  however, 
the  changes  which  ensue  in  the  chyme  after  its  passage  into  the  large  in- 
testine, are  mainly  the  absorption  of  the  more  liquid  parts,  and  the  com- 
pletion of  the  changes  which  were  proceeding  in  the  small  intestine,^ — the 
process  being  assisted  by  the  secretion  of  the  numerous  tubular  glands 
therein  present. 

Faeces. — By  these  means  the  contents  of  the  large  intestine,  as  they 
proceed  toward  the  rectum,  become  more  and  more  solid,  and  losing  their 
more  liquid  and  nutrient  parts,  gradually  acquire  the  odor  and  consist- 
ence characteristic  of  fceces.  After  a  sojourn  of  uncertain  duration  in 
the  sigmoid  flexure  of  the  colon,  or  in  the  rectum,  they  are  finally  ex- 
pelled by  the  act  of  def ascation. 

The  average  quantity  of  solid  faecal  matter  evacuated  by  the  human 
adult  in  twenty-four  hours  is  about  six  or  eight  ounces. 

Composition  of  F^ces. 

Water   733-00 

Solids   267-00 

Special  excrementitious  constituents: — Excretin,  ^ 
excretoleic  acid  (Marcet),  and  stercorin  (Aus- 
tin Flint). 

Salts: — Chiefly  phosphate  of  magnesium  and  phos- 
phate of  calcium,  with  small  quantities  of  iron, 
soda,  lime,  and  silica. 

Insoluble  residue  of  the  food  (chiefly  starch  grains, 

woody  tissue,  particles  of  cartilage  and  fibrous  )■  267-00 
tissue,  undigested  muscular  fibres  or  fat,  and 
the  like,  with  insoluble  substances  accidentally 
introduced  with  the  food). 

Mucus,  epithelium,  altered  coloring  matter  of  bile, 
fatty  acids,  etc. 

Varying  quantities  of  other  constituents  of  bile, 
and  derivatives  from  them. 

Length  of  Intestinal  Digestive  Period. — The  time  occupied  by 
the  journey  of  a  given  portion  of  food  from  the  stomach  to  the  anus, 
varies  considerably  even  in  health,  and  on  this  account,  probably,  it  is 
that  such  different  opinions  have  been  expressed  in  regard  to  the  subject. 
About  twelve  hours  are  occupied  by  the  journey  of  an  ordinary  meal 


288 


HAND-BOOK  OF  PHYSIOLOGY. 


through  the  small  intestine,  and  twenty-four  to  thirty-six  hours  by  the 
passage  through  the  large  bowel.  (Brinton.) 

Defaecation. — Immediately  before  the  act  of  voluntary  expulsion  of 
faeces  {clef cecat ion)  there  is  usually,  first  an  inspiration,  as  in  the  case  of 
coughing,  sneezing,  and  vomiting;  the  glottis  is  then  closed,  and  the 
diaphragm  fixed.  The  abdominal  muscles  are  contracted  as  in  expira- 
tion; but  as  the  glottis  is  closed,  the  whole  of  their  pressure  is  exercised 
on  the  abdominal  contents.  The  sphincter  of  the  rectum  being  relaxed, 
the  evacuation  of  its  contents  takes  place  accordingly;  the  effect  being, 
of  course,  increased  by  the  peristaltic  action  of  the  intestine.  As  in  the 
other  actions  just  referred  to,  there  is  as  much  tendency  to  the  escape  of 
the  contents  of  the  lungs  or  stomach  as  of  the  rectum;  but  the  pressure 
is  relieved  only  at  the  orifice,  the  sphincter  of  which  instinctively  or  in- 
voluntarily yields  (see  Fig.  144). 

Nervous  Mechanism  of  Defaecation. — The  anal  sphincter  muscle 
is  normally  in  a  state  of  tonic  contraction.  The  nervous  centre  which 
governs  this  contraction  is  probably  situated  in  the  lumbar  region  of  the 
spinal  cord,  inasmuch  as  in  cases  of  division  of  the  cord  above  this  region 
the  sphincter  regains,  after  a  time,  to  some  extent  the  tonicity  which  is 
lost  immediately  after  the  operation.  By  an  effort  of  the  will,  acting 
through  the  centre,  the  contraction  may  be  relaxed  or  increased.  In  ordi- 
nary cases  the  apparatus  is  set  in  action  by  the  gradual  accumulation  of 
faeces  in  the  sigmoid  flexure  and  rectum  pressing  against  the  sphincter 
and  causing  its  relaxation;  this  sensory  impulse  acting  through  the  brain 
and  reflexly  through  the  spinal  centre.  Peristaltic  action,  especially  of  the 
sigmoid  flexure  in  pressing  onward  the  faeces  against  the  sphincter,  is  a 
very  important  part  of  the  act. 

The  Gases  contained  in  the  Stomach  and  Intestines. — Under 
ordinary  circumstances,  the  alimentary  canal  contains  a  considerable 
quantity  of  gaseous  matter.  Any  one  who  has  had  occasion,  in  a  post- 
mortem examination,  either  to  lay  open  the  intestines,  or  to  let  out  the 
gas  which  they  contain,  must  have  been  struck  by  the  small  space  after- 
ward occupied  by  the  bowels,  and  by  the  large  degree,  therefore,  in  which 
the  gas,  which  naturally  distends  them,  contributes  to  fill  the  cavity  of 
the  abdomen.  Indeed,  the  presence  of  air  in  the  intestines  is  so  constant, 
and,  within  certain  limits,  the  amount  in  health  so  uniform,  that  there 
can  be  no  doubt  that  its  existence  here  is  not  a  mere  accident,  but  in- 
tended to  serve  a  definite  and  important  purpose,  although,  probably,  a 
mechanical  one. 

Sources. — The  sources  of  the  gas  contained  in  the  stomach  and 
bowels  may  be  thus  enumerated: — 

1.  Air  introduced  in  the  act  of  swallowing  either  food  or  saliva;  2. 
Gases  developed  by  the  decomposition  of  alimentary  nuittcr  or  of  the 


DIGESTION. 


289 


secretions  and  excretions  mingled  with  it  in  the  stomach  and  intestines; 
3.  It  is  probable  that  a  certain  mutual  interchange  occurs  between  the 
gases  contained  in  the  alimentary  canal,  and  those  present  in  the  blood 
of  these  gastric  and  intestinal  blood-vessels;  but  the  conditions  of  the 
exchange  are  not  known,  and  it  is  very  doubtful  whether  anything  like  a 
true  and  definite  secretion  of  gas  from  the  blood  into  the  intestines  or 
stomach  ever  takes  place.  There  can  be  no  doubt,  however,  that  the  in- 
testines may  be  the  proper  excretory  organs  for  many  odorous  and  other 
substances,  either  absorbed  from  the  air  taken  into  the  lungs  in  inspira- 
tion, or  absorbed  in  the  upper  part  of  the  alimentary  canal,  again  to  be 
excreted  at  a  portion  of  the  same  tract  lower  down — in  either  case  as- 
suming rapidly  a  gaseous  form  after  their  excretion,  and  in  this  way, 
perhaps,  obtaining  a  more  ready  egress  from  the  body.  It  is  probable 
that,  under  ordinary  circumstances,  the  gases  of  the  stomach  and  intes- 
tines are  derived  chiefly  from  the  second  of  the  sources  which  have  been 
enumerated  (Brinton). 


Composition  of  Gases  coktaiited  ix  the  Alimentary  Canal. 


(tabulated  from  various  authorities  by  brinton.) 


Whence  obtained. 

Composition  by  Volume. 

Oxygen. 

Nitrog. 

Carbon. 
Acid. 

Hydrog. 

Carburet. 
Hydrogen. 

Sulphuret. 
Hydrogen. 

11 

71 

14 

4 

Small  Intestines  .    .  . 

32 

30 

38 

1  " 

66 

12 

8  • 

13 

35 

57 

6 

8 

j>  trace 

46 

43 

11 

J 

Expelled  ])er  anum  .  . 

22 

41 

19 

19 

2 

Movements  of  the  Intestines. — It  remains  only  to  consider  the 
manner  in  which  the  food  and  the  several  secretions  mingled  with  it  are 
moved  through  the  intestinal  canal,  so  as  to  be  slowly  subjected  to  the 
influence  of  fresh  portions  of  intestinal  secretion,  and  as  slowly  exposed 
to  the  absorbent  power  of  aU  the  villi  and  blood-vessels  of  the  mucous 
membrane.  The  movement  of  the  intestines  is  peristaltic  or  vermicular, 
and  is  effected  by  the  alternate  contractions  and  dilatations  of  successive 
portions  of  the  intestinal  coats.  The  contractions,  which  may  commence^ 
at  any  point  of  the  intestine,  extend  in  a  wave-like  manner  along  the  tube. 
In  any  given  portion,  the  longitudinal  muscular  fibres  contract  first,  or 
more  than  the  circular;  they  draw  a  portion  of  the  intestine  upward,  or, 
as  it  were,  backward,  over  the  substance  to  be  propelled,  and  then  the^ 
circular  fibres  of  the  same  portion  contracting  in  succession  from  abovo 
downward,  or,  as  it  were,  from  behind  forward,  press  on  the  substance 
into  the  portion  next  below,  in  which  at  once  the  same  succession  of  action 
next  ensues.  These  movements  take  place  slowly,  and,  in  health,  are  com- 
VoL.  I.— 19. 


290 


HAND-BOOK  OF  PHYSIOLOGY. 


monly  unperceived  by  the  mind;  but  they  are  perceptible  when  they  are 
accelerated  under  the  influence  of  any  irritant. 

The  movements  of  the  intestines  are  sometimes  retrograde;  and  there 
is  no  hindrance  to  the  backward  movement  of  the  contents  of  the  small 
intestine.  But  almost  complete  security  is  afforded  against  the  passage 
of  the  contents  of  the  large  into  the  small  intestine  by  the  ileo-caecal 
valve.  Besides, — the  orifice  of  communication  between  the  ileum  and 
caecum  (at  the  borders  of  which  orifice  are  the  folds  of  mucous  membrane 
which  form  the  valve)  is  encircled  with  muscular  fibres^  the  contraction 
of  which  prevents  the  undue  dilatation  of  the  orifice. 

Proceeding  from  above  downward,  the  muscular  fibres  of  the  large 
intestine  become,  on  the  whole,  stronger  in  direct  proportion  to  the  greater 
strength  required  for  the  onward  moving  of  the  faeces,  which  are  gradually 
becoming  firmer.  The  greatest  strength  is  in  the  rectum,  at  the  termi- 
nation of  which  the  circular  unstriped  muscular  fibres  form  a  strong  band 
called  the  internal  sphincter;  while  an  external  sphincter  muscle  with 
striped  fibres  is  placed  rather  lower  down,  and  more  externally,  and  as 
we  have  seen  above,  holds  the  orifice  close  by  a  constant  slight  tonic  con- 
traction. 

Experimental  irritation  of  the  brain  or  cord  produces  no  evident  or  con- 
stant effect  on  the  movements  of  the  intestines  during  life;  yet  in  conse- 
quence of  certain  conditions  of  the  mind  the  movements  are  accelerated  or 
retarded;  and  in  paraplegia  the  intestines  appear  after  a  time  much  weak- 
ened in  their  power,  and  costiveness,  with  a  tympanitic  condition,  ensues. 
Immediately  after  death,  irritation  of  both  the  symjDathetic  and  pneumo- 
gastric  nerves,  if  not  too  strong,  induces  genuine  peristaltic  movements  of 
the  intestines.  Violent  irritation  stops  the  movements.  These  stimuli  act, 
no  doubt,  not  directly  on  the  muscular  tissue  of  the  intestine,  but  on  the 
ganglionic  plexus  before  referred  to. 

Influence  of  the  Nervous  System  on  Intestinal  Digestion. — 
As  in  the  case  of  the  oesophagus  and  stomach,  the  peristaltic  movements  of 
the  intestines  are  directly  due  to  reflex  action  through  the  ganglia  and  nerve 
fibres  distributed  so  abundantly  in  their  walls  (p.  255);  the  presence  of 
chyme  acting  as  the  stimulus,  and  few  or  no  movements  occurring  when 
the  intestines  are  empty.  The  intestines  are,  moreover,  connected  with 
the  higher  nerve-centres  by  the  splanchnic  nerves,  as  well  as  other 
branches  of  the  sympathetic  which  come  to  them  from  the  caliac  and 
other  abdominal  plexuses. 

The  splanchnic  nerves  are  in  relation  to  the  intestinal  movements, 
inhibitory — these  movements  being  retarded  or  stopped  wlien  the  splancli- 
nics  are  irritated.  As  the  vaso-motor  nerves  of  the  intestines,  the  splanch- 
nics  are  also  much  concerned  in  intestinal  digestion. 


CHAPTER  IX. 


ABSORPTION. 

The  process  of  Absorption  has,  for  one  of  its  objects,  the  introduction 
into  the  blood  of  fresh  materials  from  the  food  and  air,  and  of  whatever 
comes  into  contact  with  the  external  or  internal  surfaces  of  the  body; 
and,  for  another,  the  gradual  removal  of  parts  of  the  body  itself,  when 
they  need  to  be  renewed.  In  both  these  offices,  i.e.,  in  both  absorption 
from  without  and  absorption  from  within,  the  process  manifests  some 
variety,  and  a  very  wide  rai^ge  of  action;  and  in  both  two  sets  of  vessels 
are,  or  may  be,  concerned,  namely,  the  Blood-vessels,  and  the  Lymph- 
vessels  or  Lymphatics  to  which  the  term  Absorbents  has  been  also  applied. 

The  Lymphatic  Vessels  akd  Glai^ds. 

Distribution. — The  principal  vessels  of  the  lymphatic  system  are,  in 
structure  and  general  appearance,  like  very  small  and  thin-walled  veins, 
and  like  them  are  provided  with  valves.  By  one  extremity  they  com- 
mence by  fine  microscopic  branches,  the  lymphatic  capillaries  or  lymph- 
capillaries,  in  the  organs  and  tissues  of  the  body,  and  by  their  other  ex- 
tremities they  end  directly  or  indirectly  in  two  trunks  which  open  into  the 
large  veins  near  the  heart  (Fig.  206).  Their  contents,  the  lymph  and 
chyle,  unlike  the  blood,  pass  only  in  one  direction,  namely,  from  the  fine 
branches  to  the  trunk  and  so  to  the  large  veins,  on  entering  which  they 
are  mingled  with  the  stream  of  blood,  and  form  part  of  its  constituents. 
Remembering  the  course  of  the  fluid  in  the  lymphatic  vessels,  viz.,  its 
passage  in  the  direction  only  toimrd  the  large  veins  in  the  neighborhood 
of  the  heart,  it  will  readily  be  seen  from  Fig.  206  that  the  greater  part  of 
the  contents  of  the  lymphatic  system  of  vessels  passes  through  a  com- 
paratively large  trunk  called  the  thoracic  duct,  which  finally  empties  its 
contents  into  the  blood-stream,  at  the  junction  of  the  internal  jugular 
and  subclavian  veins  of  the  left  side.  There  is  a  smaller  duct  on  the 
right  side.  The  lymphatic  vessels  of  the  intestinal  canal  are  called  lacteals; 
because,  during  digestion,  the  fluid  contained  in  them  resembles  milk  in 
appearance;  and  the  lymph  in  the  lacteals  during  the  period  of  digestion 
is  called  chyle.    There  is  no  essential  distinction,  however,  between  lac- 


292 


HAND-BOOK  OF  PHYSIOLOGY. 


teals  and  lymphatics.  In  some  parts  of  their  course  all  lymphatic  vessels 
pass  through  certain  bodies  called  lymphatic  glands. 

Lymphatic  vessels  are  distributed  in  nearly  all  parts  of  the  body. 
Their  existence,  however,  has  not  yet  been  determined  in  the  placenta,  the 
umbilical  cord,  the  membranes  of  the  ovum,  or  in  any  of  the  non- vascular 
parts,  as  the  nails,  cuticle,  hair  and  the  like. 


Lymphatics  of  head  and 
neck,  right. 

Right  internal  jugular  vein. 
Right  subclavian  vein  


Lymphatics  of  right  arm. 


Receptaculum  chyli. 


Lymphatics  of  lower  ex- 
tremities. 


Lymphatics  of  head  and 
neck,  left. 

Thoracic  duct. 

Left  subclavian  vein. 


Thoracic  duct. 


LacteaJs. 


Lymphatics  of  lower  ex- 
tremities. 


Fig.  206.— Diagram  of  the  principal  groups  of  lymphatic  vessels  (from  Quain). 


Origin  of  Lymph  Capillaries. — The  lymphatic  capiUaries  com- 
mence most  commonly  either  in  closely-meshed  networks,  or  in  irregular 
lacunar  spaces  between  the  various  structures  of  which  the  different 
organs  are  composed.  Such  irregular  spaces,  forming  what  is  now 
termed  the  lymph-can alicidar  system,  have  been  shown  to  exist  in  many 
tissues.  In  serous  membranes,  such  as  the  omentum  and  mesentery,  they 
occur  as  a  connected  system  of  very  irregular  branched  spaces  partly  occu- 
pied by  connective-tissue  corpuscles,  and  both  in  tliese  and  in  many  other 
tissues  are  found  to  communicate  freely  with  reguhir  lymphatic  vessels. 
In  many  cases,  though  they  are  formed  mostly  by  the  chinks  and  crannies 
between  the  blood-vessels,  secreting  ducts,  and  other  parts  which  may 


ABSORPTION. 


293 


happen  to  form  the  framework  of  the  organ  in  which  they  exist,  they 
are  lined  by  a  distinct  layer  of  endothelium. 

The  lacteals  offer  an  illustration  of  another  mode  of  origin,  namely, 
in  blind  dilated  extremities  (Figs.  192  and  193);  but  there  is  no  essen- 
tial difference  in  structure  between  these  and  the  lymphatic  capillaries  of 
other  parts. 

Structure  of  Lymph  Capillaries.— The  structure  of  lymphatic 
capillaries  is  very  similar  to  that  of  blood-capillaries:  their  walls  consist 
of  a  single  layer  of  endothelial  cells  of  an  elongated  form  and  sinuous 
outline,  which  cohere  along  their  edges  to  form  a  delicate  membrane. 


Fig.  207.— Lymphatics  of  central  tendon  of  rabbit's  diaphragm,  stained  with  silver  nitrate.  The 
ground  substance  has  been  shaded  diagrammatically  to  bring  out  the  lymphatics  clearly.  I.  Lym- 
phatics hned  by  long  narrow  endothelial  cells,  and  showing  v.  valves  at  frequent  intervals  (Schofield). 

They  differ  from  blood  capillaries  mainly  in  their  larger  and  very  varia- 
ble calibre,  and  in  their  numerous  communications  with  the  spaces  of 
the  lymph-canalicular  system. 

Communications  of  the  Lymphatics. — The  fluid  part  of  the  blood 
constantly  exudes  or  is  strained  through  the  walls  of  the  blood-capillaries, 
so  as  to  moisten  all  the  surrounding  tissues,  and  occupies  the  interspaces 
which  exist  among  their  different  elements.  These  same  interspaces  have 
been  shown,  as  just  stated,  to  form  the  beginnings  of  the  lymph-capilla- 
ries; and  the  latter,  therefore,  are  the  means  of  collecting  the  exuded 
blood-plasma,  and  returning  that  part  which  is  not  directly  absorbed  by 
the  tissues  into  the  blood-stream.  For  many  years,  the  notion  of  the 
existence  of  any  such  channels  between  the  blood-vessels  and  lymph-ves- 
sels as  would  admit  blood-corpuscles,  has  been  given  up;  observations 
having  proved  that,  for  the  passage  of  such  corpuscles,  it  is  not  necessary 


294 


HAND-BOOK  OF  PHYSIOLOGY. 


to  assume  the  presence  of  any  special  channels  at  all,  inasmuch  as  blood- 
corpuscles  can  pass  bodily,  without  much  difficulty,  through  the  walls  of 
the  blood-capillaries  and  small  veins  (p.  159),  and  could  pass  with  still 
less  trouble,  probably,  through  the  comparatively  ill-defined  walls  of  the 
capillaries  which  contain  lymph. 


Fig.  208.— Lymphatic  vessels  of  the  head  and  neck  and  the  upper  part  of  the  trunk  (Mascagni). 
1-6.—  The  chest  and  pericardium  have  been  opened  on  the  left  side,  and  the  left  mamma  detached  and 
thrown  outward  over  the  left  arm,  so  as  to  expose  a  great  part  of  its  deep  surface.  The  principal 
lymphatic  vessels  and  glands  are  shown  on  the  side  of  the  head  and  face,  and  in  the  neck,  axilla,  and 
mediastinum.  Between  the  left  internal  jugular  vein  and  the  common  carotid  artery,  the  upper  as- 
cending part  of  the  thoracic  dvict  marked  1,  and  above  this,  and  descending  to  2,  the  arch  and  last 
part  of  the  duct.  The  termination  of  the  upper  lymjihatics  of  the  diaphragm  in  the  mediastinal 
glands,  as  well  as  the  cardiac  and  the  deep  mammary  lymphatics,  is  also  shoAra. 

It  is  worthy  of  note  that,  in  many  animals,  both  arteries  and  veins, 
especially  the  latter,  are  often  found  to  be  more  or  less  completely  en- 
sheathed  in  large  lymphatic  channels.  In  turtles,  crocodiles,  and  many 
other  animals,  the  abdominal  aorta  is  enclosed  in  a  large  lymphatic  vessel. 

Stomata, — In  certain  parts  of  the  body  openings  exist  by  which 
lymphatic  capillaries  directly  communicate  with  parts  hitherto  supposed 
to  be  closed  cavities.  If  the  peritoneal  cavity  be  injected  with  milk,  an 
injection  is  obtained  of  the  plexus  of  lymphatic  vessels  of  the  central 
tendon  of  the  diaphragm  (Fig.  207);  and  on  removing  a  small  portion  of 
the  central  tendon,  with  its  peritoneal  surface  uninjured,  and  examining 


ABSORPTION. 


295 


the  process  of  absorption  under  the  microscope,  the  milk-globules  run 
toward  small  natural  openings  or  stomata  between  the  epithelial  cells,  and 
disappear  by  passing  vortex-like  through  them.  The  stomata,  which 
have  a  roundish  outline,  are  only  wide  enough  to  admit  two  or  three  milk- 
globules  abreast,  and  never  exceed  the  size  of  an  epithelial  cell. 


Fig.  209.  Fig.  210. 


Fig.  209.— Superficial  lymphatics  of  the  forearm  and  palm  of  the  hand,  1-5.  5.  Two  small  glands 
at  the  bend  of  the  arm.  6.  Radial  lymphatic  vessels.  7.  IJlnar  lymphatic  vessels.  8,  8.  Palmar  arch 
of  lymphatics.  9,  9.  Outer  and  inner  sets  of  vessels,  b.  Cephalic  vein.  d.  Radial  vein.  e.  Median 
vein.  /.  Ulnar  vein.   The  lymphatics  are  represented  as  lying  on  the  deep  fascia.  (Mascagni.) 

Fig.  210.— Superficial  lymphatics  of  right  groin  and  upper  part  of  thigh,  1-6.  1,  upper  inguinal 
glands.  2.  2',  Lower  inguinal  or  femoral  glands.  3,  3'.  Plexus  of  lymphatics  in  the  course  of  the 
long  sai^henous  vein.  (Mascagni.) 

Pseudostomata. — When  absorption  into  the  lymphatic  system  takes 
place  in  membranes  covered  by  epithelium  or  endothelium  through  the 
interstitial  or  intercellular  cement-substance,  it  is  said  to  take  place 
through  pseudostomata. 


29G 


HAND-BOOK  OF  PHYSIOLOGY. 


Demonstration  of  Lymphatics  of  Diaphragyn. — The  stomata  on  the 
peritoneal  surface  of  the  diaphragm  are  the  openings  of  short  vertical 
canals  which  lead  up  into  the  lymphatics,  and  are  lined  by  cells  like  those 
of  germinating  endothelium  (p.  23).  By  introducing  a  solution  of  Berlin 
blue  into  the  peritoneal  cavity  of  an  animal  shortly  after  death,  and  sus- 
pending it,  head  downward,  an  injection  of  the  lymphatic  vessels  of  the 
diaphragm,  through  the  stomata  on  its  peritoneal  surface,  may  readily  be 
obtained,  if  artificial  respiration  be  carried  on  for  about  half  an  hour.  In 
this  way  it  has  been  found  that  in  the  rabbit  the  lymphatics  are  arranged 
between  the  tendon  bundles  of  the  centrum  tendineuai;  and  they  are 
heiice  termed  interfascicular.  The  centrum  tendineum  is  coated  by 
endothelium  on  its  pleural  and  peritoneal  surfaces,  and  its  substance  con- 
sists of  tendon  bundles  arranged  in  concentric  rings  toward  the  pleural 
side  and  in  radiating  bundles  toward  the  peritoneal  side. 


Fig.  211.— Peritoneal  surface  of  septum  cisternae  lymphaticae  magmse  of  frog.  The  stomata,  some 
of  which  are  open,  some  coUapsed,  are  surrounded  by  germinating  endotheUum.    x  160.  (Klein.) 

The  lymphatics  of  the  anterior  half  of  the  diaphragm  open  into  those 
of  the  anterior  mediastinum,  while  those  of  the  posterior  half  pass  into  a 
lymphatic  vessel  in  the  posterior  mediastinum,  which  soon  enters  the  tho- 
racic duct.  Both  these  sets  of  vessels,  and  the  glands  into  which  they 
pass,  are  readily  injected  by  the  method  above  described;  and  there  can 
be  little  doubt  that  during  life  the  flow  of  lymph  along  these  channels  is 
chiefly  caused  by  the  action  of  the  diaphragm  during  respiration.  As 
it  descends  in  inspiration,  the  spaces  between  the  radiating  tendon  bun- 
dles dilate,  and  lymph  is  sucked  from  the  peritoneal  cavity,  through  the 
widely  open  stomata,  into  the  interfascicular  lymphatics.  During  expira- 
tion, the  spaces  betAveen  the  concentric  tendon  bundles  dilate,  and  the 
lymph  is  squeezed  into  the  lymphatics  toward  the  pleural  surface.  (Klein. ) 
It  thus  appears  probable  that  during  health  there  is  a  continued  sucking 
in  of  lymph  from  the  .peritoneum  into  the  lymphatics  by  the  "pumping'' 
action  of  the  diaphragm;  and  there  is  doubtless  an  equally  continuous 
exudation  of  fluid  from  the  genei-al  serous  surface  of  the  })eritoneum. 
When  this  balance  of  transudation  and  absorption  is  disturbed,  either  by 
increased  transudation  or  some  impediment  to  absorption,  an  accumula- 
tion of  fluid  necessarily  takes  place  (ascites). 

Stomata  have  been  found  in  the  pleura;  and  as  they  may  be  presumed 
to  exist  in  other  serous  membranes,  it  would  seem  as  if  the  serous  cavities, 


ABSOEPTION. 


297 


hitherto  supposed  closed,  form  but  a  large  lymph-sinus,  or  widening  out, 
so  to  speak,  of  the  lymph-capillary  system  with  which  they  directly  com- 
municate. 

Structure  of  Lymphatic  Vessels.— The  larger  vessels  are  very  like 
veins,  having  an  external  coat  of  fibro-cellular  tissue,  with  elastic  fila- 
ments; within  this,  a  thin  layer  of  fibro-cellular  tissue,  with  plain  mus- 
cular fibres,  which  have,  principally,  a  circular  direction,  and  are  much 
more  abundant  in  the  small  than  in  the  larger  vessels;  and  again,  within 
this,  an  inner  elastic  layer  of  longitudinal  fibres,  and  a  lining  of  epithe- 
lium; and  numerous  valves.  The  valves,  constructed  like  those  of  veins, 
and  with  the  free  edges  turned  toward  the  heart,  are  usually  arranged  in 
pairs,  and,  in  the  small  vessels,  are  so  closely  placed,  that  when  the  vessels 
are  full,  the  valves  constricting  them  where  their  edges  are  attached,  give 
them  a  peculiar  beaded  or  knotted  appearance. 

Current  of  the  Lymph. — With  the  help  of  the  valvular  mechanism 
(1)  all  occasional  pressure  on  the  exterior  of  the  lymphatic  and  lacteal 
vessels  propels  the  lymph  toward  the  heart:  thus  muscular  and  other 
external  pressure  accelerates  th6  flow  of  the  lymph  as  it  does  that  of  the 
blood  in  the  veins.  The  actions  of  (2)  the  muscular  fibres  of  the  small 
intestine,  and  probably  the  layer  of  organic  muscle  present  in  each  intes- 
tinal villus,  seem  to  assist  in  propelling  the  chyle:  for,  in  the  small  intes- 
tine of  a  mouse,  the  chyle  has  been  seen  moving  with  intermittent  pro- 
pulsions that  appeared  to  correspond  with  the  peristaltic  movements  of 
the  intestine.  But  for  the  general  propulsion  of  the  lymph  and  chyle,  it 
is  probable  that,  together  with  (3)  the  vis  a  tergo  resulting  from  absorp- 
tion (as  in  the  ascent  of  sap  in  a  tree),  and  from  external  pressure,  some 
of  the  force  may  be  derived  (4)  from  the  contractility  of  the  vessels  own 
walls.  The  respiratory  movements,  also,  (5)  favor  the  current  of  lymph 
through  the  thoracic  duct  as  they  do  the  current  of  blood  in  the  thoracic 
veins  (p.  20G). 

Lymphatic  Glands  are  small  round  or  oval  compact  bodies  varying 
in  size  from  a  hempseed  to  a  bean,  interposed  in  the  course  of  the  lym- 
phatic vessels,  and  through  which  the  chief  part  of  the  lymph  passes  in 
*ts  course  to  be  discharged  into  the  blood-vessels.    They  are  found  in 
<reat  numbers  in  the  mesentery,  and  along  the  great  vessels  of  the  abdo- 
len,  thorax,  and  neck;  in  the  axilla  and  groin;  a  few  in  the  popliteal 
pace,  but  not  further  down  the  leg,  and  in  the  arm  as  far  as  the  elbow. 
Some  lymphatics  do  not,  however,  pass  through  glands  before  entering 
he  thoracic  duct. 

Structure. — A  lymphatic  gland  is  covered  externally  by  a  capsule  of 
connective  tissue,  generally  containing  some  unstriped  muscle.  At  the 
inner  side  of  the  gland,  which  is  somewhat  concave  (Jiihis)  (Fig.  212,  a), 
the  capsule  sends  processes  inward  in  which  the  blood-vessels  are  con- 
tained, and  these  join  with  other  processes  called  traheculce  (Fig.  215,  i.r.) 


298 


HAND-BOOK  OF  PHYSIOLOGY. 


prolonged  from  the  inner  surface  of  the  part  of  the  capsule  covering  the 
convex  or  outer  part  of  the  gland;  they  have  a  structure  similar  to  that 
of  the  capsule,  and  entering  the  gland  from  all  sides,  and  freely  commu- 
nicating, form  a  fibrous  supporting  stroma.  The  interior  of  the  gland 
is  seen  on  section,  even  when  examined  with  the  naked  eye,  to  be  made 
up  of  two  parts,  an  outer  or  cortical  (Fig.  212,  c,  c),  which  is  light- 
colored,  and  an  inner  of  redder  appearance,  the  medullary  portion  (Fig. 
212).  In  the  outer  or  cortical  part  of  the  gland  (Fig.  215,  c)  the  inter- 
vals between  the  trabeculse  are  comparatively  large  and  more  or  less  trian- 


FlG.  212. 


Fig.  213. 


Fig.  212.— Section  of  a  mesenteric  gland  from  the  ox,  slightly  magnified,  o,  Hilus ;  6  (in  the  cen- 
tral part  of  the  figure),  medullary  substance;  c,  cortical  substance  with  indistinct  alveoh;  d,  capsule 
(KciUiker.) 

Fig.  213.— From  a  vertical  section  through  the  capsule,  cortical  sinus  and  peripheral  portion  of 
follicle  of  a  human  compound  lymphatic  gland.  The  section  had  been  shaken,  so  as  to  get  rid  of  most 
of  the  lymph  corpuscles.  A.  Outer  stratum  of  capsule,  consisting  of  bundles  of  fibrous  Tissue  cut  at 
various  angles.  B.  Inner  stratum,  showing  fibres  of  connective  tissue  with  nuclei  of  flattened  con- 
nective-tissue-corpuscles. Beneath  this  (between  B  and  C)  is  the  lymph-sinus  or  lymph-patli.  contain- 
ing a  reticulum  coated  by  flat  nucleated  endothehal  cells.  C.  Fine  uucleatetl  endothelial  membrane, 
marking  boundary  of  the  lymph-follicle.  The  rest  of  the  section  from  C  to  E  is  the  adenoitl  tissue  of 
the  lymph-follicle,  which  consists  of  a  fine  reticulum,  E,  with  niunerous  Ij-mph-corpuscles.  D.  They 
are  so  closely  packed  that  the  adenoid  reticulum  is  invisible  till  the  section  has  been  shaken  so  as  to 
dislodge  a  number  of  the  lymph-corpuscles,    x  350.   (Klein  and  Noble  Smith.) 


gular,  the  intercommunicating  spaces  being  termed  alveoli;  whilst  in  the 
more  central  or  medullary  part  a  finer  meshwork  is  formed  by  the  more 
free  anastomosis  of  the  trabecular  processes.  In  the  alveoli  of  the  cortex 
and  ill  the  meshwork  formed  by  the  trabecule^  in  the  medulla,  is  contained 
the  proper  gland  structure.  In  the  former  it  is  arranged  as  follows  (Fig. 
215):  occupying  the  central  and  chief  part  of  each  alveolus,  is  a  more  or 
less  wedge-shaped  mass  {l.h.)  of  adenoid  tissue,  densely  packed  with  lymph 
corpuscles;  but  at  the  perijiliery  surrounding  the  central  portion  and  im- 
mediately next  the  capsule  and'  trabeculae,  is  a  more  open  meshwork  of 
adenoid  tissue  constituting  the  lymph  siiius  or  clia)niel  (Ls.),  and  contain- 


ABSORPTION. 


299 


ing  fewer  lymph  corpuscles.  The  central  mass  is  enclosed  in  endothelium, 
the  cells  of  which  join  by  their  processes,  the  processes  of  the  adenoid 
framework  of  the  lymph  sinus.  The  trabeculae  are  also  covered  with 
endothelium.    The  lining  of  the  central  mass  does  not  prevent  the  passage 


Fig.  214. — Section  of  meduEary  substance  of  an  inguinal  gland  of  an  ox:  a,  a,  glandular  substance 
or  pulp  forming  rounded  cords  joining  in  a  continuous  net  (dark  in  the  figure):  c,  c,  trabfeculse;  the 
space,  6,  &,  between  these  and  the  glandular  substance  is  the  lymph-sinus,  washed  clear  of  corpuscles 
and  traversed  by  filaments  of  retiform  connective-tissue,    x  90.  (Kolliker.) 


Fig.  21,5.— Diagrammatic  section  of  Lymphatic  gland,  a.  L,  Afferent;  e.  I.,  efferent  lymphatics; 
C,  cortical  substance;  I.  h.,  reticulating  cords  of  medvillary  substance:  I.  s.,  lymph-sinus;  c,  fibrous 
coat  sending  in  trabeculae;  f.  r.,  into  the  substance  of  the  gland.  (Sharpey.) 

of  fluids  and  even  of  corpuscles  into  the  lymph  sinus.  The  framework  of 
the  adenoid  tissue  of  the  lymph  sinus  is  nucleated,  that  of  the  central 
mass  is  non-nucleated.    At  the  inner  part  of  the  alveolus,  the  wedge- 


300 


HAND-BOOK  OF  PHYSIOLOGY. 


shixped  central  mass  bifurcates  (Fig.  215)  or  divides  into  two  or  more 
smaller  rounded  or  cord-like  masses,  and  here  joining  with  those  from  the 
other  alveoli,  form  a  much  closer  arrangement  of  the  gland  tissue  (Fig. 
214,  a)  than  in  the  cortex;  spaces  (Fig.  214,  h)  are  left  within  those 
anastomosing  cords,  in  Avhich  are  found  portions  of  the  trabecular  mesh- 
work  and  the  continuation  of  the  lymph  sinus  {b,  c). 

The  essential  structure  of  lymphatic-gland  substance  resembles  that 
which  was  described  as  existing,  in  a  simple  form,  in  the  interior  of  the 
solitary  and  agminated  intestinal  follicles. 

The  lymph  enters  the  gland  by  several  afferent  vessels  (Fig.  215,  a.l.) 
which  open  beneath  the  capsule  into  the  lymph -channel  or  lymph-path; 


Fig.  216.— a  small  portion  of  medullary  substance  from  a  mesenteric  gland  of  the  ox.  d,  d.  tra- 
beculae;  a,  part  of  a  cord  of  glandular  substances  from  which  all  but  a  few  of  the  lymph-corpuscles 
have  been  washed  out  to  show  its  supporting  mesh  work  of  retif  orm  tissue  and  its  capillar3-  blood-ves- 
sels (which  have  been  injected,  and  ai-e  dark  in  the  figm-e);  b,  b,  Ij'mph-sinus,  of  which  the  retiform 
tissue  is  represented  only  at  c,  c.    x  300.  (Kolliker.) 

at  the  same  time  they  lay  aside  all  their  coats  except  the  endothelial 
lining,  which  i^^  continuous  with  the  lining  of  the  lymph-path.  The 
efferent  vessels  (Fig.  215,  e.I.)  begin  in  the  medullary  part  of  the  gland, 
and  are  continuous  with  the  lymph-path  here  as  the  afferent  vessels  were 
with  the  cortical  portion;  the  endotlielium  of  one  is  continuous  with  that 
of  the  other. 

The  efferent  vessels  leave  the  gland  at  tlie  In'Iu,'^,  tlie  more  or  less  con- 
cave inner  side  of  tlio  gland,  and  generally  either  at  once  or  very  soon 
after  join  togetlier  to  form  a  single  vessel. 

Blood-vessels  which  enter  and  leave  the  ghmd  at  the  hihis  are  freely 
distributed  to  the  trabecuhir  tissue  and  to  tlie  glaiid-})ulp  (Fig.  21G). 


ABSORPTIOTT. 


301 


The  tonsils,  in  part,  and  Peyer^s  glands  of  the  intestine,  are  really 
lymphatic  glands,  and  doubtless  discharge  similar  functions. 

The  Lymph  and  Chyle. 

The  lymph,  contained  in  the  lymphatic  vessels,  is,  under  ordinary  cir- 
cumstances, a  clear,  transparent,  and  yellowish  fluid.  It  is  devoid  of 
smell,  is  slightly  alkaline,  and  has  a  saline  taste.  As  seen  with  the 
microscope  in  the  small  transparent  vessels  of  the  tail  of  the  tadpole,  it 
usually  contains  no  corpuscles  or  particles  of  any  kind;  and  it  is  only  in 
the  larger  trunks  in  which  any  corpuscles  are  to  be  found.  These  corpus- 
cles are  similar  to  colorless  blood-corpuscles.  The  fluid  in  which  the  cor- 
puscles float  is  albuminous,  and  contains  no  fatty  particles  or  molecular  base; 
but  is  liable  to  variations  according  to  the  general  state  of  the  blood,  and 
to  that  of  the  organ  from  which  the  lymph  is  derived.  As  it  advances 
toward  the  thoracic  duct,  and  after  passing  through  the  lymphatic  glands, 
it  becomes  spontaneously  coagulable  and  the  number  of  corpuscles  is  much 
increased.  The  fluid  contained  in  the  lacteals  is  clear  and  transparent 
during  fasting,  and  differs  in  no  respect  from  ordinary  lymph;  but,  during 
digestion,  it  becomes  milky,  and  is  termed  chyle. 

Chyle  is  an  opaque,  whitish,  milky  fluid,  neutral  or  slightly  alkaline 
in  reaction.  Its  whiteness  and  opacity  are  due  to  the  presence  of  innu- 
merable particles  of  oily  or  fatty  matter,  of  exceedingly  minute  though 
nearly  uniform  size,  measuring  on  the  average  about  -g-o^-gr  inch. 
These  constitute  what  is  termed  the  molecular  hase  of  chyle.  Their 
number,  and  consequently  the  opacity  of  the  chyle,  are  dependent  upon 
the  quantity  of  fatty  matter  contained  in  the  food.  The  fatty  nature  of 
the  molecules  is  made  manifest  by  their  solubility  in  ether,  and,  when 
the  ether  evaporates,  by  their  being  deposited  in  various-sized  drops  of 
oil.  Each  molecule  probably  consists  of  oil  coated  over  with  albumen,  in 
the  manner  in  which  oil  always  becomes  covered  when  set  free  in  minute 
drops  in  an  albuminous  solution.  This  is  proved  when  water  or  dilute 
acetic  acid  is  added  to  chyle,  many  of  the  molecules  are  lost  sight  of,  and 
oil-drops  appear  in  their  place,  as  the  investments  of  the  molecules  have 
been  dissolved,  and  their  oily  contents  have  run  together. 

Except  these  molecules,  the  chyle  taken  from  the  villi  or  from  lacteals 
near  them,  contains  no  other  solid  or  organized  bodies.  The  fluid  in 
which  the  molecules  float  is  albuminous,  and  does  not  spontaneously 
coagulate.  But  as  the  chyle  passes  on  toward  the  thoracic  duct,  and 
especially  while  it  traverses  one  or  more  of  the  mesenteric  glands,  it  is 
elaborated.  The  quantity  of  molecules  and  oily  particles  gradually  dimin- 
ishes; cells,  to  which  the  name  of  chyle-corpuscles  is  given,  are  devel- 
oped in  it;  and  it  acquires  the  property  of  coagulating  spontaneously. 
The  higher  in  the  thoracic  duct  the  chyle  advances,  the  more  is  it,  in  all 


302 


HAND-BOOK  OF  PHYSIOLOGY. 


these  respects,  developed;  the  greater  is  the  number  of  chyle-corpuscles, 
and  the  larger  and  firmer  is  the  clot  which  forms  in  it  when  withdrawn 
and  left  at  rest.  Such  a  clot  is  like  one  of  blood  without  the  red  cor- 
puscles, having  the  chyle  corpuscles  entangled  in  it,  and  the  fatty  matter 
forming  a  white  creamy  film  on  the  surface  of  the  serum.  But  the  clot 
of  chyle  is  softer  and  moister  than  that  of  blood.  Like  blood,  also,  the 
chyle  often  remains  for  a  long  time  in  its  vessels  without  coagulating,  but 
coagulates  rapidly  on  being  removed  from  them.  The  existence  of  the 
materials  which,  by  their  union,  form  fibrin,  is,  therefore,  certain;  and 
their  increase  appears  to  be  commensurate  with  that  of  the  corpuscles. 

The  structure  of  the  chyle -corpuscles  was  described  when  speaking  of 
the  white  corpuscles  of  the  blood,  with  which  they  are  identical. 

Chemical  Composition  of  Lymph  and  Chyle. — From  what  has 
been  said,  it  will  appear  that  perfect  chyle  and  lymph  are,  in  essential 
characters,  nearly  similar,  and  scarcely  differ,  except  in  the  preponder- 
ance of  fatty  and  proteid  matter  in  the  chyle. 


Chemical  Composition  of  Lymph  and  Chyle.    (Owen  Eees.) 

I,  II.  III. 

Lymph  Chyle     Mixed  Lymph  & 

(Donkey).  (Donkey).    Chyle  (Human). 

Water       .       .       .       .    96-536  90-237  90-48 

Solids        ....     3-454  9-763  9-52 


Solids— 

Proteids,  including  Serum-  ) 

Albumin,   Fibrin,    and  [  1-320         3*886  7*08 

Globulin     .       .       .  ) 
Extractives,  including  in  (i 

and  i)  Sugar,  Urea,  Leu- 

cin  and  Cholesterin 
Fatty  matter  . 
Salts  .... 


•1.559 

1-565 

•108 

a  trace 

3-601 

•92 

-585 

•711 

•44 

From  the  above  analyses  of  lymph  and  chyle,  it  appears  that  they  con- 
tain essentially  the  same  constituents  that  are  found  in  the  blood.  Their 
composition,  indeed,  differs  from  that  of  the  blood  in  degree  rather  than 
in  kind.  They  do  not,  however,  unless  by  accident,  contain  colored  cor- 
puscles. 

Quantity. — The  quantity  which  would  pass  into  a  cat's  blood  in 
twenty-four  hours  has  been  estimated  to  be  equal  to  about  one-sixtli  of 
the  weight  of  the  whole  body.  And,  since  tlie  estimated  weight  of  the 
blood  in  cats  is  to  the  weight  of  their  bodies  as  1  -7,  the  quantity  of  lymph 
daily  traversing  the  thoracic  duct  would  appear  to  be  about  equal  to  tlie 
quantity  of  blood  at  any  time  contained  in  the  animals.    By  another  series 


ABSORPTION. 


303 


of  experiments,  the  quantity  of  lymph  traversing  the  thoracic  duct  of  a 
dog  in  twenty-four  hours  was  found  to  be  about  equal  to  two-thirds  of 
the  blood  in  the  body.    (Bidder  and  Schmidt.) 

Absorption  by  the  Lacteals. — During  the  passage  of  the  chyme 
along  the  whole  tract  of  the  intestinal  canal,  its  completely  digested  parts 
are  absorbed  by  the  blood-vessels  and  lacteals  distributed  in  the  mucous 
membrane.  The  blood-vessels  appear  to  absorb  chiefly  the  dissolved  por- 
tions of  the  food,  and  these,  including  especially  the  albuminous  and  sac- 
charine, they  imbibe  without  choice;  whatever  can  mix  with  the  blood 
passes  into  the  vessels,  as  will  be  presently  described.  But  the  lacteals 
appear  to  absorb  only  certain  constituents  of  the  food,  including  par- 
ticularly the  fatty  portions.  The  absorption  by  both  sets  of  vessels  is 
carried  on  most  actively  but  not  exclusively,  in  the  villi  of  the  small  in- 
testine; for  in  these  minute  processes,  both  the  capillary  blood-vessels  and 
the  lacteals  are  brought  almost  into  contact  with  the  intestinal  contents. 
There  seems  to  be  no  doubt  that  absorption  of  fatty  matters  during  diges- 
tion, from  the  contents  of  the  intestines,  is  effected  chiefly  between  the 
epifchelial  cells  which  line  the  intestinal  tract  (Watney),  and  especially 
those  which  clothe  the  surface  of  the  villi.  Thence,  the  fatty  particles 
are  passed  on  into  the  interior  of  the  lacteal  vessels  (Fig.  216,  a),  but 
how  they  pass,  and  what  laws  govern  their  so  doing,  are  not  at  present 
exactly  known. 

The  process  of  absorption  is  assisted  by  the  pressure  exercised  on  the 
contents  of  the  intestines  by  their  contractile  walls;  and  the  absorption  of 
fatty  particles  is  also  facilitated  by  the  presence  of  the  bile,  and  the  pan- 
creatic and  intestinal  secretions,  which  moisten  the  absorbing  surface. 
Tor  it  has  been  found  by  experiment,  that  the  passage  of  oil  through  an 
animal  membrane  is  made  much  easier  when  the  latter  is  impregnated 
with  an  alkaline  fluid. 

Absorption  by  the  Lymphatics. — The  real  source  of  the  lymph, 
and  the  mode  in  which  its  absorption  is  effected  by  the  lymphatic  vessels, 
were  long  matters  of  discussion.  But  the  problem  has  been  much  sim- 
plified by  more  accurate  knowledge  of  the  anatomical  relations  of  the 
lymphatic  capillaries.  The  lymph  is,  without  doubt,  identical  in  great 
part  with  the  liquor  sanguMs,  which,  as  before  remarked,  is  always 
exuding  from  the  blood-capillaries  into  the  interstices  of  the  tissues  in 
♦which  they  lie;  and  as  these  interstices  form  in  most  parts  of  the  body 
the  beginnings  of  the  lymphatics,  the  source  of  the  lymph  is  sufficiently 
obvious.  In  connection  with  this  may  be  mentioned  the  fact  that  changes 
in  the  character  of  the  lymph  correspond  very  closely  with  changes  in  the 
character  of  either  the  whole  mass  of  blood,  or  of  that  in  the  vessels  of 
the  part  from  which  the  lymph  is  exuded.  Thus  it  appears  that  the 
coagulability  of  the  lymph  is  directly  proportionate  to  that  of  the  blood; 
and  that  when  fluids  are  injected  into  the  blood-vessels  in  sufficient  quan- 


304 


HAND-BOOK  OF  PHYSIOLOGY. 


tity  to  distend  them,  the  injected  substance  may  be  almost  directly 
afterward  found  in  the  lymphatics. 

Some  other  matters  than  those  originally  contained  in  the  exuded 
liquor  sanguinis  may,  however,  find  their  way  with  it  into  the  lymphatic 
vessels.  Parts  which  having  entered  into  the  composition  of  a  tissue, 
and,  having  fulfilled  their  purpose,  require  to  be  removed,  may  not  be 
altogether  excrementitious,  but  may  admit  of  being  reorganized  and 
adapted  again  for  nutrition;  and  these  may  be  absorbed  by  the  lym- 
phatics, and  elaborated  with  the  other  contents  of  the  lymph  in  passing 
through  the  glands. 

Ly^nph- Hearts. —In  reptiles  and  some  birds,  an  important  auxiliary 
to  the  movement  of  the  lymph  and  chyle  is  supplied  in  certain  muscular 
sacs,  named  lymph-hearts  (Fig.  217),  and  it  has  been  shown  that  the 
caudal  heart  of  the  eel  is  a  lymph-heart  also.  The  number  and  position 
of  these  organs  vary.  In  frogs  and  toads  there  are  usually  four,  two 
anterior  and  two  posterior;  in  the  frog,  the  posterior  lymph-heart  on  each 
side  is  situated  in  the  ischiatic  region,  just  beneath  the  skin;  the  anterior 
lies  deeper,  just  over  the  transverse  process  of  the  third  vertebra.  Into 
each  of  these  cavities  several  lymphatics  open,  the  orifices  of  the  vessels 
being  guarded  by  valves,  which  prevent  the  retrograde  passage  of  the 


Fig.  217.— Lymphatic  heart  (9  lines  long,  4  lines  broad)  of  a  large  species  of  serpent,  the  Python 
bi^ttatus.  4.  The  external  cellular  coat.  5.  The  thick  muscular  coat.  Four  muscular  columns  run 
across  its  cavity,  which  communicates  with  three  Ij-mphatics  (1— only  one  is  seen  here),  and  with  two 
veins  (2,  2).  6.  The  smooth  lining  membrane  of  the  cavity.  7.  A  small  appendage,  or  auricle,  the  cav- 
ity of  which  is.  continuous  with  that  of  the  rest  of  the  organ  (after  E.  Weber). 


lymph.  From  each  heart  a  single  vein  proceeds  and  conveys  the  lymph 
directly  into  the  venous  system.  In  the  frog,  the  inferior  lymphatic 
heart,  on  each  side,  pours  its  lymph  into  a  branch  of  tlie  ischiatic  vein; 
by  the  superior,  tlie  lymph  is  forced  into  a  branch  of  tlie  jugular  vein, 
which  issues  from  its  anterior  surface,  and  wliich  becomes  turgid  each 
time  that  the  sac  contracts.  Blood  is  prevented  from  passing  from  the 
vein  into  the  lymphatic  heart  by  a  valve  at  its  orifice. 

The  muscular  coat  of  these  hearts  is  of  variable  tliickness;  in  some 
cases  it  can  only  be  discovered  by  means  of  tlie  microscope;  but  in  every 
case  it  is  composed  of  striped  fibres.  The  contractions  of  the  lieart  are 
rhythmical,  occurring  about  sixty  times  in  a  minute,  slowly,  and,  in  com- 
parison with  those  of  the  blood-hearts,  feebly.    The  pulsations  of  the 


ABSORPTION. 


305 


cervical  pair  are  not  always  synchronous  with  those  of  the  pair  in  the 
ischiatic  region,  and  even  the  corresponding  sacs  of  opposite  sides  are  not 
always  synchronous  in  their  action. 

Unlike  the  contractions  of  the  blood-heart,  those  of  the  lymph-heart 
appear  to  be  directly  dependent  upon  a  certain  limited  portion  of  the 
spinal  cord.  For  Volkmann  found  that  so  long  as  the  portion  of  spinal 
cord  corresponding  to  the  third  vertebra  of  the  frog  was  uninjured,  the 
cervical  pair  of  lymphatic  hearts  continued  pulsating  after  all  the  rest  of 
the  spinal  cord  and  the  brain  were  destroyed;  while  destruction  of  this 
portion,  even  though  all  other  parts  of  the  nervous  centres  were  unin- 
jured, instantly  arrested  the  heart's  movements.  The  posterior,  or  ischi- 
atic, pair  of  lymph-hearts  were  found  to  be  governed,  in  like  manner,  by 
the  portion  of  spinal  cord  corresponding  to  the  eighth  vertebra.  Division 
of  the  posterior  spinal  roots  did  not  arrest  the  movements;  but  division 
of  the  anterior  roots  caused  them  to  cease  at  once. 


Absorption  by  Blood-vessels. — In  the  absorption  by  the  lym- 
phatic or  lacteal  vessels  just  described,  there  appears  something  like  the 
exercise  of  choice  in  the  materials  admitted  into  them.  But  the  , absorp- 
tion by  blood-vessels  presents  no  such  appearance  of  selection  of  materials; 
rather,  it  appears,  that  every  substance,  whether  gaseous,  liquid,  or  a 
soluble,  or  minutely  divided  solid,  may  be  absorbed  by  the 
blood-vessels,  provided  it  is  capable  of  permeating  their 
walls,  and  of  mixing  with  the  blood;  and  that  of  all  such 
substances,  the  mode  and  measure  of  absorption  are  deter- 
mined solely  by  their  physical  or  chemical  properties  and 
conditions,  and  by  those  of  the  blood  and  the  walls  of  the 
blood-vessels. 

Osmosis. — The  phenomena  are,  indeed,  to  a  great  ex- 
tent, comparable  to  that  passage  of  fluids  through  mem- 
brane, which  occurs  quite  independently  of  vital  conditions, 
and  the  earliest  and  best  scientific  investigation  of  which 
was  made  by  Dutrochet.    The  instrument  which  he  employed 
in  his  experiments  was  named  an  endosmometer .    It  may  con- 
sist of  a  graduated  tube  expanded  into  an  open-mouthed  bell 
at  one  end,  over  which  a  portion  of  membrane  is  tied  (Fig. 
218).     If  now  the  bell  be  filled  with  a  solution  of  a  salt- 
say  sodium  chloride,  and  be  immersed  in  water,  the  water 
will  pass  into  the  solution,  and  part  of  the  sali  will  pass  out    F1G.218.  En- 
into  the  water;  the  water,  however,  will  pass  into  the  solu- 
tion much  more  rapidly  than  the  salt  will  pass  out  into  the  water,  and  the 
diluted  solution  will  rise  in  the  tube.    To  this  passage  of  fiuids  througk 
membrane  the  term  Osmosis  is  applied. 

The  nature  of  the  membrane  used  as  a  septum,  and  its  affinity  for  the 
fluids  subjected  to  experiment,  have  an  important  influence,  as  might  be 
anticipated,  on  the  rapidity  and  duration  of  the  osmotic  current.  Thus 
Vol.  I.— 20. 


306 


HAND-BOOK  OF  PHYSIOLOGY. 


if  a  piece  of  ordinary  bladder  be  used  as  the  septum  between  water  and 
alcoliol,  the  current  is  almost  solely  from  the  water  to  the  alcohol,  on 
account  of  the  much  greater  affinity  of  water  for  tliis  kind  of  membrane; 
while,  on  the  other  hand,  in  the  case  of  a  membrane  of  caoutchouc,  the 
alcohol,  from  its  greater  affinity  for  this  substance,  would  pass  freely  into 
the  water. 

Osmosis  by  Blood-vessels. — Absorption  by  blood-vessels  is  the 
consequence  of  their  walls  being,  like  the  membranous  septum  of  the 
endosmometer,  porous  and  capable  of  imbibing  fluids,  and  of  the  blood 
being  so  composed  that  most  fluids  will  mingle  with  it.  The  process  of 
absorption,  in  an  instructive,  though  very  imperfect  degree,  may  be  ob- 
served in  any  portion  of  vascular  tissue  removed  from  the  body.  If  such 
a  one  be  placed  in  a  vessel  of  water,  it  will  shortly  swell,  and  become 
heavier  and  moister,  through  the  quantity  of  water  imbibed  or  soaked 
into  it;  and  if  now,  the  blood  contained  in  any  of  its  vessels  be  let  out,  it 
will  be  found  diluted  with  water,  which  has  been  absorbed  by  the  blood- 
vessels and  mingled  with  the  blood.  The  water  round  the  piece  of  tissue 
also  will  become  blood-stained;  and  if  all  be  kept  at  perfect  rest,  the  stain 
derived  from  the  solution  of  the  coloring  matter  of  the  blood  (together 
with  which  chemistry  would  detect  some  of  the  albumen  and  other  parts 
of  the  liquor  sanguinis)  will  spread  more  widely  every  day.  The  same 
will  happen  if  the  piece  of  tissue  be  placed  in  -a  saline  solution  instead  of 
water,  or  in  a  solution  of  coloring  or  odorous  matter,  either  of  which  will 
give  tlaeir  tinge  or  smell  to  the  blood,  and  receive,  in  exchange,  the  color 
of  the  blood.  , 

Colloids  and  Crystalloids. — Various  substances  have  been  classified 
according  to  the  degree  in  which  they  possess  the  property  of  passing, 
when  in  a  state  of  solution  in  water,  through  membrane;  those  which 
pass  freely,  inasmuch  as  they  are  usually  capable  of  crystallization,  being 
termed  crystalloids,  and  those  which  pass  with  difficulty,  on  account  of 
their,  physically,  glue-like  characters,  colloids.  (Graham.) 

This  distinction,  however,  between  colloids  and  crystalloids,  which  is 
made  the  basis  of  their  classification,  is  by  no  means  the  only  difference 
between  them.  The  colloids,  besides  the  absence  of  power  to  assume  a 
crystalline  form,  are  characterized  by  their  inertness  as  acids  or  bases,  and 
feebleness  in  all  ordinary  chemical  relations.  Examples  of  them  are 
found  in  albumin,  gelatin,  starch,  hydrated  alumina,  hydrated  silicic 
acid,  etc. ;  while  the  crystalloids  are  characterized  by  qualities  the  reverse 
of  those  just  mentioned  as  belonging  to  colloids.  Alcohol,  sugar,  and 
ordinary  saline  substances  are  examples  of  crystalloids. 

Rapidity  of  Absorption. — Tlio  rapidit}^  with  which  matters  may  be 
absorbed  from  the  stomach,  })roba])]y  by  the  blood-vessels  chiefly,  and 
diffused  through  the  textures  of  the  body,  may  be  gathered  from  the  liis- 
tory  of  some  experiments.    From  these  it  appears  that  even  in  a  quarter 


ABSORPTIOIT. 


307 


of  an  hour  after  being  given  on  an  empty  stomach,  lithium  chloride  may 
be  diffused  into  all  the  vascular  textures  of  the  body,  and  into  some  of 
the  non-vascular,  as  the  cartilage  of  the  hip- joint,  as  well  as  into  the 
aqueous  humor  of  the  eye.  Into  the  outer  part  of  the  crystalline  lens  it 
may  pass  after  a  time,  varying  from  half  an  hour  to  an  hour  and  a  half. 
Lithium  carbonate,  when  taken  in  five  or  ten-grain  doses  on  an  empty 
stomach,  may  be  detected  in  the  urine  in  5  or  10  minutes;  or,  if  the 
stomach  be  full  at  the  time  of  taking  the  dose,  in  20  minutes.  It  may 
sometimes  be  detected  in  the  urine,  moreover,  for  six,  seven,  or  eight 
days.    (Bence  Jones.) 

Some  experiments  on  the  absorption  of  various  mineral  and  vegetable 
poisons,  have  brought  to  light  the  singular  fact,  that,  in  some  cases, 
absorption  takes  place  more  rapidly  from  the  rectum  than  from  the 
stomach.  Strychnia,  for  example,  when  in  solution,  produces  its  poison- 
ous effects  much  more  speedily  when  introduced  into  the  rectum  than 
into  the  stomach.  When  introduced  in  the  solid  form,  however,  it  is 
absorbed  more  rapidly  from  the  stomach  than  from  the  rectum,  doubtless 
because  of  the  greater  solvent  property  of  the  secretion  of  the  former  than 
of  that  of  the  latter.  (Savory.) 

With  regard  to  the  degree  of  absorption  by  living  blood-vessels,  much 
depends  on  the  facility  with  which  the  substance  to  be  absorbed  can  pene- 
trate the  membrane  or  tissue  which  lies  between  it  and  the  blood-vessels. 
Thus,  absorption  will  hardly  take  place  through  the  epidermis,  but  is 
quick  when  the  epidermis  is  removed,  and  the  same  vessels  are  covered 
with  only  the  surface  of  the  cutis,  or  with  granulations.  In  general,  the 
absorption  through  membranes  is  in  an  inverse  proportion  to  the  thick- 
ness of  their  epithelia;  so  that  the  urinary  bladder  of  a  frog  is  traversed 
in  less  than  a  second;  and  the  absorption  of  poisons  by  the  stomach  or 
lungs  appears  sometimes  accomplished  in  an  immeasurably  small  time. 

Conditions  for  Absorption. — 1.  The  substance  to  be  absorbed  must, 
as  a  general  rule,  be  in  the  liquid  or  gaseous  state,  or,  if  a  solid,  must  be 
soluble  in  the  fluids  with  which  it  is  brought  in  contact.  Hence  the 
marks  of  tattooing,  and  the  discoloration  produced  by  silver  nitrate  taken 
internally,  remain.  Mercury  may  be  absorbed  even  in  the  metallic  state; 
and  in  that  state  may  pass  into  and  remain  in  the  blood-vessels,  or  be 
deposited  from  them;  and  such  substances  as  exceedingly  finely-divided 
charcoal,  when  taken  into  the  alimentary  canal,  have  been  found  in  tJie 
mesenteric  veins;  the  insoluble  materials  of  ointments  may  also  be  rubbed 
into  the  blood-vessels;  but  there  are  no  facts  to  determine  how  these 
various  substances  effect  their  passage.  Oil,  minutely  divided,  as  in  an 
emulsion,  will  pass  slowly  into  blood-vessels,  as  it  will  through  a  filter 
moistened  with  water;  and,  without  doubt,  fatty  matters  find  their  way 
into  the  blood-vessels  as  well  as  the  lymph-vessels  of  the  intestinal  canal, 
although  the  latter  seem  to  be  specially  intended  for  their  absorption. 


308 


HAND-BOOK  OF  PHYSIOLOGY. 


2.  The  less  dense  the  fluid  to  be  absorbed,  the  more  speedy,  as  a  gen- 
eral rule,  is  its  absorption  by  the  living  blood-vessels.  Hence  the  rapid 
absorption  of  water  from  the  stomach;  also  of  weak  saline  solutions;  but 
with  strong  solutions,  there  appears  less  absorption  into,  than  effusion 
from,  the  blood-vessels. 

3.  The  absorption  is  the  less  rapid  the  fuller  and  tenser  the  blood-vessels 
are;  and  the  tension  may  be  so  great  as  to  hinder  altogether  the  entrance 
of  more  fluid.  Thus,  if  water  is  injected  into  a  dog's  veins  to  repletion, 
poison  is  absorbed  very  slowly;  but  when  the  tension  of  the  vessels  is 
diminished  by  bleeding,  the  poison  acts  quickly.  So,  when  cupping-glasses 
are  placed  over  a  poisoned  wound,  they  retard  the  absorption  of  the  poison 
not  only  by  diminishing  the  velocity  of  the  circulation  in  the  part,  but 
by  filling  all  its  vessels  too  full  to  admit  more. 

On  the  same  ground,  absorption  is  the  quicker  the  more  rapid  the  cir- 
culation of  the  blood;  not  because  the  fluid  to  be  absorbed  is  more  quickly 
imbibed  into  th-e  tissues,  or  mingled  with  the  blood,  but  because  as  fast 
as  it  enters  the  blood,  it  is  carried  away  from  the  part,  and  the  blood  being 
constantly  renewed,  is  constantly  as  fit  as  at  the  first  for  the  reception  of 
the  substance  to  be  absorbed. 


CHAPTEE  X. 


ANIMAL  HEAT. 

The  Average  Temperature  of  the  human  body  in  those  internal  parts 
which  are  most  easily  accessible,  as  the  mouth  and  rectum,  is  from  98*5° 
to  99-5°  F.  (36-9°— 37-4°  C).  In  different  parts  of  the  external  surface 
of  the  human  body  the  temperature  varies  only  to  the  extent  of  two  or 
three  degrees  (F.),  when  all  are  alike  protected  from  cooling  influences; 
and  the  difference  which  under  these  circumstances  exists,  depends  chiefly 
upon  the  different  degrees  of  blood-supply.  In  the  arm-pit — the  most 
convenient  situation,  under  ordinary  circumstances,  for  examination  by 
the  thermometer — the  average  temperature  is  98*6°  F.  (36*9°  0.).  In 
different  internal  parts,  the  variation  is  one  or  two  degrees;  those  parts 
and  organs  being  warmest  which  contain  most  blood,  and  in  which  there 
occurs  the  greatest  amount  of  chemical  change,  e.g.,  the  glands  and  the 
muscles;  and  the  temperature  is  highest,  of  course,  when  they  are  most 
actively  working:  while  those  tissues  which,  subserving  only  a  mechanical 
function,  are  the  seat  of  least  active  circulation  and  chemical  change,  are 
the  coolest.  These  differences  of  temperature,  however,  are  actually  but 
slight,  on  account  of  the  provisions  which  exist  for  maintaining  uniform- 
ity of  temperature  in  different  parts. 

Circumstances  causing  Variations  in  Temperature. — The 
chief  circumstances  by  which  the  temperature  of  the  healthy  body  is  influ- 
enced are  the  following: — Age;  Sex;  Period  of  the  day;  Exercise;  Cli- 
mate and  Season;  Food  and  Drinh. 

Age. — The  average  temperature  of  the  new-born  child  is  only  about  1° 
F.  (-54°  C.)  above  that  proper  to  the  adult;  and  the  difference  becomes 
still  more  trifling  during  infancy  and  early  childhood.  The  temperature 
falls  to  the  extent  of  about  '2° — '5°  F.  from  early  infancy  to  puberty,  and 
by  about  the  same  amount  from  puberty  to  fifty  or  sixty  years  of  age.  In 
old  age  the  temperature  again  rises,  and  approaches  that  of  infancy;  but 
although  this  is  the  case,  yet  the  power  of  resisting  cold  is  less  in  them — 
exposure  to  a  low  temperature  causing  a  greater  reduction  of  heat  than  in 
young  person?. 


The  same  rapid  diminution  of  temperature  has  been  observed  to  occur 
in  the  new-born  young  of  most  carnivorous  and  rodent  animals  when  they 
are  removed  from  the  parent,  the  temperature  of  the  atmosphere  being 


310 


HAND-BOOK  OF  PHYSIOLOGY. 


between  50°  and  53*5°  F.  (10°-12°  C);  whereas  while  lying  close  to  the 
body  of  the  mother,  tlieir  temperature  is  only  2  or  3  degrees  F.  lower 
than  hers.    The  same  law  applies  to  the  young  of  birds. 

Sex. — The  average  temperature  of  the  female  would  appear  to  be  very 
slightly  higher  than  that  of  the  male. 

Period  of  the  Day. — The  temperature  undergoes  a  gradual  alteration, 
to  the  extent  of  about  1°  to  1-5°  F.  (-54 — -8°  C.)  in  the  course  of  the  day 
and  night;  the  minimum  being  at  night  or  in  the  early  morning,  the 
maximmn  late  in  the  afternoon. 

Exercise. — Active  exercise  raises  the  temperature  of  the  body  from  1° 
to  2°  F.  (-54° —  1.08°  C).  This  may  be  partly  ascribed  to  generally  in- 
creased combustion-processes,  and  partly  to  the  fact,  that  every  muscular 
contraction  is  attended  by  the  development  of  one  or  two  degrees  of  heat 
in  the  acting  muscle;  and  that  the  heat  is  increased  according  to  the 
number  and  rapidity  of  these  contractions,  and  is  quickly  diffused  by  the 
blood  circulating  from  the  heated  muscles.  Possibly,  also,  some  heat 
may  be  generated  in  the  various  movements,  stretchings,  and  recoilings 
of  the  other  tissues,  as  the  arteries,  whose  elastic  walls,  alternately  dilated 
and  contracted,  may  give  out  some  heat,  just  as  caoutchouc  alternately 
stretched  and  recoiling  becomes  hot.  But  the  heat  thus  developed  cannot 
be  great.  The  great  apparent  increase  of  heat  during  exercise  depends, 
in  a  great  measure,  on  the  increased  circulation  and  quantity  of  blood, 
and,  therefore,  greater  heat,  in  parts  of  the  body  (as  the  skin,  and  espe- 
cially the  skin  of  the  extremities),  which,  at  the  sanie  time  that  they  feel 
more  acutely  than  others  any  changes  of  temperature,  are,  under  ordi- 
nary conditions,  by  some  degrees  colder  than  organs  more  centrally 
situated. 

Climate  and  Season. — The  temperature  of  the  human  body  is  the  same 
in  temperate  and  tropical  climates.  (Johnson,  Boileau,  Furnell.)  In 
summer  the  temperature  of  the  body  is  a  little  higher  than  in  winter;  the 
difference  amounting  to  about  a  third  of  a  degree  F.  (Wunderlich.) 

Food  and  Drink.  The  effect  of  a  meal  upon  the  temperature  of  a  body 
is  but  small.  A  very  slight  rise  usually  occurs.  Cold  alcoholic  drinks 
depress  the  temperature  somewhat  ('5°  to  1°  F.).  Warm  alcoholic 
drinks,  as  well  as  warm  tea  and  coffee,  raise  the  temperature  (about  '5°  F.). 

In  disease  the  temperature  of  the  body  deviates  from  the  normal  stand- 
ard to  a  greater  extent  than  would  be  anticipated  from  the  slight  effect 
of  external  conditions  during  health.  Thus,  in  some  diseases,  as  pneu- 
monia and  typhus,  it  occasionally  rises  as  high  as  106°  or  107°  F.  (41° — 
41 -0°  C);  and  considerably  higher  temperatures  have  been  noted.  In 
Asiatic  cholera,  on  the  other  hand,  a  thermonu"^ter  placed  in  the  mouth 
may  sometimes  rise  only  to  77°  or  79°  F.  (25°— '.^G -2°  C). 

The  temperature  maintained  by  Mammalia  in  an  active  state  of  life. 


ANIMAL  HEAT. 


811 


according  to  the  tables  of  Tiedemann  and  Rudolphi,  averages  101° 
(38.3°  0.).  The  extremes  recorded  by  them  were  96°  and  106°,  the  former 
in  the  narwhal,  the  latter  in  a  bat  (Vespertilio  pipistrella).  In  Birds,  the 
average  is  as  high  as  107°  (41-2°  C);  the  highest  temperature,  111*25° 
(46*2°  0.);  being  in  the  small  species,  the  linnets,  etc.  Among  Reptiles, 
while  the  medium  they  were  in  was  75°  (23 '9°  0.)  their  average  tempera- 
ture was  82*5°  (31  "2°  0.).  As  a  general  rule,  their  temperature,  though 
it  falls  with  that  of  the  surrounding  medium,  is,  in  temperate  media,  two 
or  more  degrees  higher;  and  though  it  rises  also  with  that  of  the  medium, 
yet  at  very  high  degrees  it  ceases  to  do  so,  and  remains  even  lower  than 
that  of  the  medium.  Fish  and  invertebrata  present,  as  a  general  rule,  the 
same  temperature  as  the  medium  in  which  they  live,  whether  that  be  high 
or  low;  only  among  fish,  the  tunny  tribe,  with  strong  hearts  and  red 
meat-like  muscles,  and  more  blood  than  the  average  of  fish  have,  are 
generally  7°  (3*8°  C.)  warmer  than  the  water  around  them. 

The  difference,  therefore,  between  what  are  commonly  called  the  warm 
and  the  cold-blooded  animals,  is  not  one  of  absolutely  higher  or  lower 
temperature;  for  the  animals  which  to  us  in  a  temperate  climate  feel  cold 
(being  like  the  air  or  water,  colder  than  the  surface  of  our  bodies),  would 
in  an  external  temperature  of  100°  (37*8°  C.)  have  nearly  the  same  tem- 
perature and  feel  hot  to  us.  The  real  difi'erence  is  that  what  we  call 
warm-blooded  animals  (Birds  and  Mammalia),  have  a  certain  "permanent 
heat  in  all  atmospheres,^^  while  the  temperature  of  the  others,  which  we 
call  cold-blooded,  is  "variable  with  every  atmosphere. (Hunter.) 

The  power  of  maintaining  a  uniform  temperature,  which  Mammalia 
and  Birds  possess,  is  combined  with  the'  want  of  power  to  endure  such 
changes  of  body  temperature  as  are  harmless  to  the  other  classes;  and 
when  their  power  of  resisting  change  of  temperature  ceases,  they  suffer 
serious  disturbance  ar  die. 

Sources  and  Mode  of  Production  of  Heat  in  the  Body.— 

The  heat  which  is  produced  in  the  body  arises  from  combustion,  and  is 
due  to  the  fact  that  the  oxygen  of  the  atmosphere  taken  into  the  system 
is  combined  with  the  carbon  and  hydrogen  of  the  tissues.  Any  changes 
which  occur  in  the  protoplasm  of  the  tissues,  resulting  in  an  exhibition 
of  their  function,  is  attended  by  the  evolution  of  heat  and  also  by  the  pro- 
duction of  carbonic  acid  and  water;  and  the  more  active  the  changes, 
the  greater  the  heat  produced  and  the  greater  the  amount  of  the  carbonic 
acid  and  water  formed.  But  in  order  that  the  protoplasm  may  perform 
its  function,  the  waste  of  its  own  tissue  (destructive  metabolism),  must 
be  repaired  by  the  supply  of  food  material,  and  therefore  for  the  produc- 
tion of  heat  it  is  necessary  to  supply  food.  In  the  tissues,  therefore, 
two  processes  are  continually  going  on:  the  building  up  of  the  protoplasm 
from  the  food  (constructive  metabolism),  which  is  not  accompanied  by 
the  evolution  of  heat  but  possibly  by  the  reverse,  and  the  oxidation  of  the 
protoplastic  materials,  resulting  in  the  production  of  energy,  ty  which 
heat  is  produced  and  carbonic  acid  and  water  are  evolved.  Some  heat 
will  also  be  generated  in  the  combination  of  sulphur  and  phosphorus  with 
oxygen,  but  the  amount  thus  produced  is  but  small. 


312 


IIAXD-BOOK  OF  PHYSIOLOGY. 


It  is  not  necessary  to  assume  that  the  combustion  processes,  whicli 
ultimately  issue  iu  the  production  of  carbonic  acid  and  water,  are  as  sim- 
ple as  the  bare  statement  of  the  fact  might  seem  to  indicate.  But  com- 
plicated as  the  various  stages  of  combustion  may  be,  the  ultimate  result 
is  as  simple  as  in  ordinary  combustion  outside  the  body,  and  the  products 
are  the  same.  The  same  amount  of  heat  will  be  evolved  in  the  union 
of  any  given  quantities  of  carbon  and  oxygen,  and  of  hydrogen  and  oxy- 
gen, whether  the  combination  be  rapid  and  direct,  as  in  ordinary  combus- 
tion, or  slow  and  almost  imperceptible,  as  in  the  changes  which  occur  in 
the  living  body.  And  since  the  heat  thus  arising  will  be  distributed 
wherever  the  blood  is  carried,  every  part  of  the  body  will  be  heated  equally, 
or  nearly  so. 

This  theory,  that  the  maintenance  of  the  temperature  of  the  living 
body  depends  on  continual  chemical  change,  chiefly  by  oxidation,  of 
combustible  materials  existing  in  the  tissues,  has  long  been  established  by 
the  demonstration  that  the  quantity  of  carbon  and  hydrogen  which,  in 
a  given  tiuie,  unites  in  the  body  with  oxygen,  is  sufficient  to  account  for 
the  amotmt  of  heat  generated  in  the  animal  within  the  same  time:  an 
amount  capable  of  maintaining  the  temperature  of  the  body  at  from  98 
—100°  F.  (36-8°— 37 -8°  C),  notwithstanding  a  large  loss  by  radiation  and 
evaporation. 

It  should  be  remembered  that  heat  may  be-  introduced  into  the  body 
by  means  of  warm  drinks  and  foods,  and,  again,  that  it  is  possible  for  the 
preliminary  digestive  changes  to  be  accompanied  by  the  evolution  of  heat. 

Chief  Heat-producing  Tissues. — The  chemical  changes  which 
produce  the  body-heat  appear  to  be  especially  active  in  certain  tissues: — 

(1)  ,  In  the  Muscles,  which  form  so  large  a  part  of  the  organism.  The 
fact  that  the  manifestation  of  muscular  energy  is  always  attended  by  the 
evolution  of  heat  and  the  production  of  carbonic  acid  has  been  demon- 
strated by  actual  experiment;  and  when  not  actually  in  a  condition  of 
active  contraction,  a  metabolism,  not  so  active  but  still  actual,  goes  on, 
which  is  accompanied  by  the  manifestation  of  heat.  The  total  amount 
set  free  by  the  muscles,  therefore,  must  be  very  great;  and  it  has  been 
calculated  that  even  neglecting  the  heat  produced  by  the  quiet  metabolism 
of  muscular  tissue,  the  amount  of  heat  generated  by  muscuhir  activity 
supplies  the  principal  part  of  the  total  heat  produced  within  the  body. 

(2)  ,  In  the  Secreting  glands,  and  principally  in  the  liver  as  being  the 
largest  and  most  active.  It  has  been  found  by  experiment  that  the  blood 
leaving  the  glands  is  considerably  warmer  than  that  entering  them.  The 
metabolism  in  the  glands  is  very  active,  and,  as  we  have  seen,  the  more 
active  the  metabolism  the  greater  the  heat  produced.  (3),  In  tlie  Brain; 
the  venous  blood  having  a  higher  temperature  than  the  arterial.  It 
must  be  remembered,  however,  that  although  the  organs  al)ove  nu^itioned 
are  the  chief  heat-produciiig  parts  of  the  body,  all  living  tissues  contribute 


ANOrAL  HEAT. 


313 


their  quota,  and  this  in  direct  proportion  to  their  activity.  The  blood 
itself  is  also  the  seat  of  metabolism,  and,  therefore,  of  the  production  of 
heat;  but  the  share  which  it  takes  in  this  respect,  apart  from  the  tissues 
in  which  it  circulates,  is  very  inconsiderable. 

Regulation  of  the  Temperature  of  the  Human  Body.— The 
average  temperature  of  the  body  is  maintaijied  under  different  conditions 
of  external  circumstances  by  mechanisms  which  permit  of  (1)  variation 
in  the  amount  of  heat  got  rid  of,  and  (2)  variations  in  the  amount  of  heat 
produced  or  introduced  into  the  body.  In  healthy  warm-bloocled  animals 
the  loss  and  gain  of  heat  are  so  nearly  balanced  one  by  ihe  other  that, 
under  all  ordinary  circumstances,  a  uniform  temperature,  within  two  or 
three  degrees,  is  preserved. 

I.  Methods  of  Variation  in  the  amount  of  Heat  got  rid  of. — 
The  loss  of  heat  from  the  human  body  is  principally  regulated  by  the 
amount  lost  by  radiation  and  conduction  from  its  surface,  and  by  means 
of  the  constant  evaporation  of  water  from  the  same  part,  and  (2)  to  a 
much  less  degree  from  the  air -passages;  in  each  act  of  respiration,  heat 
is  lost  to  a  greater  or  less  extent  according  to  the  temperature  of  the 
atmosphere;  unless  indeed  the  temperature  of  the  surrounding  air  exceed 
that  of  the  blood.  We  must  remember  too  that  all  food  and  drink  which 
enter  the  body  at  a  lower  temperature  than  itself  abstract  a  small  measure 
of  heat:  while  the  urine  and  faeces  which  leave  the  body  at  about  its  own 
temperature  are  also  means  by  which  a  small  amount  is  lost. 

(a.)  Loss  of  Heat  from  the  Suiface  of  tJie  Body :  the  Skin. — By  far 
the  most  important  loss  of  heat  from  the  body, — probably  70  or  80  per 
cent,  of  the  whole  amount,  is  that  which  takes  place  by  radiation,  con- 
duction, and  evaporation  from  the  skin.  The  means  by  which  the  skin 
is  able  to  act  as  one  of  the  most  important  organs  for  regulating  the  tem- 
perature of  the  blood,  are — (1),  that  it  offers  a  large  surface  for  radiation, 
conduction,  and  evaporation;  (2),  that  it  contains  a  large  amount  of 
blood;  (3),  that  the  quantity  of  blood  contained  in  it  is  the  greater  under 
those  circumstances  which  demand  a  loss  of  heat  from  the  body,  and  vice 
versa.  For  the  circumstance  which  directly  determines  the  quantity  of 
blood  in  the  skin,  is  that  which  governs  the  supply  of  blood  to  all  the 
tissues  and  organs  of  the  body,  namely,  the  power  of  the  vaso-motor  nerves 
to  cause  a  greater  or  less  tension  of  the  muscular  element  in  the  walls  of 
the  arteries,  and,  in  correspondence  with  this,  a  lessening  or  increase  of 
the  calibre  of  the  vessels,  accompanied  by  a  less  or  greater  current  of  blood. 
A  warm  or  hot  atmosphere  so  acts  on  the  nerve  fibres  of  the  skin,  as  to 
lead  them  to  cause  in  turn  a  relaxation  of  the  muscular  fibre  of  the  blood- 
vessels; and,  as  a  result,  the  skin  becomes  full-blooded,  hot,  and  sweating; 
and  much  heat  is  lost.  With  a  low  temperature,  on  the  other  hand,  the 
blood-vessels  shrink,  and  in  accordance  with  the  consequently  diminished 
blood-supply,  the  skin  becomes  pale,  and  cold,  and  dry;  and  no  doubt  a 


314 


HAND-BOOK  OF  PHYSIOLOGY. 


similar  effect  may  be  produced  through  the  vaso-motor  centre  in  the 
medulla  and  spinal  cord.  Thus,  by  means  of  a  self- regulating  apparatus, 
the  skin  becomes  the  most  important  of  the  means  by  which  the  tempera- 
ture of  the  body  is  regulated. 

In  connection  with  loss  of  heat  by  the  skin,  reference  has  been  made 
to  that  which  occurs  both  by  jadiation  and  conduction,  and  by  evapora- 
tion; and  the  subject  of  animal  heat  has  been  considered  almost  solely 
with  regard  to  the  ordinary  case  of  man  living  in  a  medium  colder  than 
his  body,  and  therefore  losing  heat  in  all  the  w^ays  mentioned.  The  im- 
portance of  the  means,  however,  adopted,  so  to  speak,  by  the  skin  for  regu- 
lating the  temperature  of  the  body,  will  depend  on  the  conditions  by 
which  it  is  surrounded;  an  inverse  proportion  existing  in  most  cases  be- 
tween the  loss  by  radiation  and  conduction  on  the  one  hand,  and  by 
evaporation  on  the  other.  Indeed,  the  small  loss  of  heat  by  evaporation 
in  cold  climates  may  go  far  to  compensate  for  the  greater  loss  by  radia- 
tion; as,  on  the  other  hand,  the  great  amount  of  fluid  evaporated  in  hot 
air  may  remove  nearly  as  much  heat  as  is  commonly  lost  by  both  radia- 
tion and  evaporation  in  ordinary  temperatures;  and  thus,  it  is  possible 
that  the  quantities  of  heat  required  for  the  maintenance  of  a  uniform 
proper  temperature  in  various  climates  and  seasons  are  not  so  different 
as  they,  at  first  thought,  seem. 

Many  examples  may  be  given  of  the  poiuer  which  the  hody  2^ossesses  of 
resisting  the  effects  of  a  high  temperature,  in  virtue  of  evaporation  from 
the  skin.  Blagden  and  others  supported  a  temperature  varying  between 
198°~211°  F.  (92°— 100°  C.)  in  dry  air  for  several  minutes;  and  in  a 
subsequent  experiment  he  remained  eight  minutes  in  a  temperature  of 
260°  F.  (126-5°  C).  "The  workmen  of  Sir  F.  Chantrey  were  accustomed 
to  enter  a  furnace,  in  w^hich  his  moulds  were  dried,  whilst  the  floor  was 
red-hot  and  a  thermometer  in  the  air  stood  at  350°  F.  (177*8°  C);  and 
Chabert,  the  fire-king,  was  in  the  habit  of  entering  an  oven  the  tempera- 
ture of  which  was  from  400°  to  600°  F.^^  (205°— 315°  C.)  (Carpenter.) 

But  such  heats  are  not  tolerable  when  the  air  is  moist  as  well  as  hot, 
so  as  to  prevent  evaporation  from  the  body.  0.  James  states,  that  in  the 
vapor  baths  of  Nero  he  was  almost  suflocated  in  a  temperature  of  112°  F. 
(44 '5°  C.  ),  while  in  the  caves  of  Testaccio,  in  which  the  air  is  drj^,  he 
was  but  little  incommoded  by  a  temperature  of  176°  F.  (80°  C).  In 
the  former,  evaporation  from  the  skin  was  impossible;  in  the  latter  it  was 
abundant,  and  the  layer  of  vapor  wliich  would  rise  from  all  the  surface 
of  the  body  would,  by  its  very  slowly  conducting  power,  defend  it  for  a 
time  from  the  full  action  of  the  external  heat. 

(The  glandular  apparatus,  by  wliich  secretion  of  fluid  from  the  skin  is 
effected,  will  be  considered  in  the  Section  on  the  Skin.) 

The  ways  by  which  the  skin  may  be  rendered  more  efficient  as  a  cool- 
ing-apparatus, by  exposure,  by  baths,  and  by  otlier  means  which  man 
instinctively  adopts  for  lowering  his  temperature  when  necessary,  are  too 
well  known  to  need  more  than  to  be  mentioned. 


ANIMAL  HEAT. 


315 


Although  under  any  ordinary  circumstances,  the  external  application 
of  cold  only  temporarily  depresses  the  temperature  to  a  slight  extent,  it 
is  otherwise  in  cases  of  high  temperature  in  fever.  In  these  cases  a  tepid 
bath  may  reduce  the  temperature  several  degrees,  and  the  effect  so  pro- 
duced lasts  in  some  cases  for  many  hours. 

(b.)  Loss  of  Heat  from  the  Lungs. — As  a  means  for  lowering  the  tem- 
perature, the  lungs  and  air-passages  are  very  inferior  to  the  skin;  although, 
by  giving  heat  to  the  air  we  breathe,  they  stand  next  to  the  skin  in  im- 
portance. As  a  regulating  power,  the  inferiority  is  still  more  marked. 
The  air  which  is  expelled  from  the  lungs  leaves  the  body  at  about  the 
temperature  of  the  blood,  and  is  always  saturated  with  moisture.  Ko 
inverse  proportion,  therefore,  exists  between  the  loss  of  heat  by  radiation 
and  conduction  on  the  one  hand,  and  by  evaporation  on  the  other.  The 
colder  the  air,  for  example,  the  greater  will  be  the  loss  in  all  ways. 
Neither  is  the  quantity  of  blood  which  is  exposed  to  the  cooling  influence 
of  the  air  diminished  or  increased,  so  far  as  is  known,  in  accordance  w^ith 
any  need  in  relation  to  temperature.  It  is  true  that  by  varying  the  num- 
ber and  depth  of  the  respirations,  the  quantity  of  heat  given  off  by  the 
lungs  may  be  made,  to  some  extent,  to  vary  also.  But  the  respiratory 
passages,  w^hile  they  must  be  considered  important  means  by  which  heat 
is  lost,  are  altogether  subordinate,  in  the  power  of  regulating  the  temper- 
ature, to  the  skin. 

(c.)  By  Clothing. — The  influence  of  external  coverings  for  the  body 
must  not  be  unnoticed.  In  warm-blooded  animals,  they  are  always 
adapted,  among  other  purposes,  to  the  maintenance  of  uniform  tempera- 
ture; and  man  adapts  for  himself  such  as  are,  for  the  same  purpose,  fitted 
to  the  various  climates  to  which  he  is  exposed.  By  their  means,  and  by 
his  command  over  food  and  fire,  he  maintains  his  temperature  on  all 
accessible  parts  of  the  surface  of  the  earth. 

II.  Methods  oi  Variation  in  the  amount  of  Heat  produced. 
— It  may  seem  to  have  been  assumed,  in  the  foregoing  pages,  that  the 
only  regulating  apparatus  for  temperature  required  by  the  human  body 
is  one  that  shall,  more  or  less,  produce  a  cooling  effect;  and  as  if  the 
amount  of  heat  produced  were  always,  therefore,  in  excess  of  that  which 
is  required.  Such  an  assumption  would  be  incorrect.  We  have  the  power 
of  regulating  the  production  of  heat,  as  well  as  its  loss. 

(a.)  By  Regulating  the  Quantity  and  Quality  of  the  Food  taken. — In 
food  we  have  a  means  for  elevating  our  temperature.  It  is  the  fuel, 
indeed,  on  which  animal  heat  ultimately  depends  altogether.  Thus, 
when  more  heat  is  wanted,  we  instinctively  take  more  food,  and  take 
such  kinds  of  it  as  are  good  for  combustion;  while  e very-day  exj^erience. 
shows  the  different  power  of  resisting  cold  jiossessed,  respectively,  by  the 
well-fed  and  by  the  starved.  In  northern  regions,  again,  and  in  the 
colder  seasons  of  more  southern  climes,  the  quantity  of  food  consumed  is 


316 


HAND-BOOK  OF  PHYSIOLOGY. 


(speaking  very  generally)  greater  than  that  consumed  by  the  same  men 
or  animals  in  opposite  conditions  of  climate  and  season.  And  the  food 
which  appears  naturally  adapted  to  the  inhabitants  of  the  coldest 
climates,  such  as  the  several  fatty  and  oily  substances,  abounds  in  carbon 
and  hydrogen,  and  is  fitted  to  combine  with  the  large  quantities  of  oxy- 
gen which,  breathing  cold  dense  air,  they  absorb  from  their  lungs. 

(b.)  By  Exercise. — In  exercise,  we  have  an  important  means  of  raising 
the  temperature  of  our  bodies  (p.  310). 

(c.)  By  Liflueiice  of  the  Nervous  System. — The  influence  of  the  nerv- 
ous system  in  modifying  the  production  of  heat  must  be  very  important, 
as  upon  nervous  influence  depends  the  amount  of  the  metabolism  of  the 
tissues.  The  experiments  and  observations  which  best  illustrate  it  are 
those  showing,  first,  that  when  the  supply  of  nervous  influence  to  a  part 
is  cut  ofi',  the  temperature  of  that  part  falls  below  its  ordinary  degree; 
and,  secondly,  that  when  death  is  caused  by  severe  injury  to,  or  removal 
of,  the  nervous  centres,  the  temperature  of  the  body  rapidly  falls,  even 
though  artificial  respiration  be  performed,  the  circulation  maintained, 
and  to  all  appearance  the  ordinary  chemical  changes  of  the  body  be  com- 
pletely effected.  It  has  been  repeatedly  noticed,  that  after  division  of 
the  nerves  of  a  limb  its  temperature  falls;  and  this  diminution  of  heat 
has  been  remarked  still  more  plainly  in  limbs  deprived  of  nervous  influ- 
ence by  paralysis. 

With  equal  certainty,  though  less  definitely,  the  influence  of  the 
nervous  system  on  the  production  of  heat,  is  shoAvn  in  the  rapid  and 
momentary  increasa  of  temperature,  sometimes  general,  at  other  times 
quite  local,  which  is  observed  in  states  of  nervous  excitement;  in  the 
general  increase^'of  warmth  of  the  body,  sometimes  amounting  to  perspi- 
ration, which  is- excited  by  passions  of  the  mind;  in  the  sudden  rush  of 
heat  to- the  face,  which  is  not  a  mere  sensation;  and  in  the  equally  rapid 
diminution  of  temperature  in  the  depressing  passions.  But  none  of  these 
instances  suffice  to  prove  that  heat  is  generated  by  mere  nervous  action, 
independent  of  any  chemical  change;  all  are  explicable,  on  the  supposi- 
tion that  the  nervous  system  alters,  by  its  power  of  controlling  the  calibre 
of  the  blood-vessels,  the  quantity  of  blood  supplied  to  a  part;  while  any 
influence  which  the  nervous  system  may  have  in  the  production  of  heat, 
apart  from  this  influence  on  the  blood-vessels,  is  an  indirect  one,  and  is 
derived,  from,  its  power  of  causing  such  nutritive  change  in  the  tissues  as 
may,  by  involving  the  necessity  of  chemical  action,  involve  the  produc- 
tion of  licat. 

InliiUtory  heat-centre. — Whether  a  centre  exists  which  regulates  the 
production  of  heat  in  Avarm-bloodcd  animals,  is  still  undecided.  Experi- 
ments liave  shown  that  exposure  to  cold  at  once  increases  the  oxygen 
taken  in,  and  the  carbonic  acid  given  out,  indicating  an  increase  in  the 
activity  of  the  metabolism  of  the  tissues,  but  that  in  animals  poisoned  by 


ANIMAL  HEAT. 


317 


urari,  exposure  to  cold  diminishes  both  the  metabolism  and  the  temper- 
ature, and  warm-blooded  animals  then  re-act  to  variations  of  the  ex- 
ternal temperature  just  in  the  same  way  as  cold-blooded.  These  experi- 
ments seem  to  suggest  that  there  is  a  centre,  to  which,  under  normal 
circumstances,  the  impression  of  cold  is  conveyed,  and  from  which  by 
efferent  nerves  impulses  pass  to  the  muscles,  whereby  an  increased  metab- 
olism is  induced,  and  so  an  increased  amount  of  heat  is  generated.  The 
centre  is  probably  situated  above  the  medulla.  Thus  in  urarized  animals, 
as  the  nerves  to  the  muscles,  the  metabolism  of  which  is  so  important 
in  the  production  of  heat,  are  paralyzed,  efferent  impulses  from  the  centre 
cannot  induce  the  necessary  metabolism  for  the  production  of  heat,  even 
though  afferent  impulses  from  the  skin,  stimulated  by  the  alteration  of 
temperature,  have  conveyed  to  it  the  necessity  of  altering  the  amount  of 
heat  to  be  produced.  The  same  effect  is  produced  when  the  medulla 
is  cut. 

Influence  of  Extreme  Heat  and  Cold. — In  connection  with  the 
regulation  of  animal  temperature,  and  its  maintenance  in  health  at  the 
normal  height,  may  be  noted  the  result  of  circumstances  too  powerful, 
either  in  raising  or  lowering  the  heat  of  the  body,  to  be  controlled  by  the 
proper  regulating  apparatus.  Walther  found  that  rabbits  and  dogs,  when 
tied  to  aboard  and  exposed  to  a  hot  sun,  reached  a  temperature  of  114*8° 
F.,  and  then  died.  Cases  of  sunstroke  furnish  us  with  several  examples 
in  the  case  of  man;  for  it  would  seem  that  here  death  ensues  chiefly  or 
solely  from  elevation  of  the  temperature.  In  many  febrile  diseases  the 
immediate  cause  of  death  appears  to  be  the  elevation  of  the  temperature 
to  a  point  inconsistent  with  the  continuance  of  life. 

The  effect  of  mere  loss  of  bodily  temperature  in  man  is  less  well  known 
than  the  effect  of  heat.  From  experiments  by  Walther,  it  appears  that 
rabbits  can  be  cooled  down  to  48°  F.  (8.9°  C),  before  they  die,  if  arti- 
ficial respiration  be  kept  up.  Cooled  down  to  64°  F.  (17.8°  C),  they 
cannot  recover  unless  external  warmth  be  applied  together  with  the 
employment  of  artificial  respiration.  Eabbits  not  cooled  below  77°  F. 
(25°  C.)  recover  by  external  warmth  alone. 


CHAPTER  XI. 


SECRETION. 

Secretion  is  the  process  by  which  materials  are  separated  from  the 
blood,  and  from  the  organs  in  which  they  are  formed,  for  the  purpose 
either  of  serving  some  ulterior  ofl&ce  in  the  economy,  or  of  being  dis- 
charged from  the  body  as  useless  or  injurious.  In  the  former  case,  the 
separated  materials  are  termed  secretions;  in  the  latter,  they  are  termed 
excretions. 

Most  of  the  secretions  consist  of  substances  which,  probably,  do  not 
pre-exist  in  the  same  form  in  the  blood,  but  require  special  organs  and  a 
process  qf  elaboration  for  their  formation,  e.g.,  the  liver  for  the  formation 
of  bile,  the  mammary  gland  for  the  formation  of  milk.  The  excretions, 
on  the  other  hand,  commonly  or  chiefly  consist  of  substances  which  exist 
ready-formed  in  the  blood,  and  are  merely  abstracted  therefrom.  If  from 
any  cause,  such  as  extensive  disease  or  extirpation  of  an  excretory  organ, 
the  separation  of  an  excretion  is  prevented,  and  an  accumulation  of  it  in 
the  blood  ensues,  it  frequently  escapes  through  other  organs,  and  may  be 
detected  in  various  fluids  of  the  body.  But  this  is  never  the  case  with 
secretions;  at  least  with  those  that  are  most  elaborated;  for  after  the 
removal  of  the  special  organs  by  which  any  of  them  is  elaborated,  it  is  no 
longer  formed.  Oases  sometimes  occur  in  which  the  secretion  continues 
to  be  formed  by  the  natural  organ,  but  not  being  able  to  escape  toward 
the  exterior,  on  account  of  some  obstruction,  is  re-absojbed  into  the  blood, 
and  afterward  discharged  from  it  by  exudation  in  other  ways;  but  these 
are  not  instances  of  true  vicarious  secretion,  and  must  not  be  thus 
regarded. 

These  circumstances,  and  their  final  destination,  are,  however,  the 
only  particulars  in  which  secretions  and  excretions  can  be  distinguished; 
for,  in  general,  the  structure  of  the  parts  engaged  in  eliminating  excre- 
tions is  as  complex  as  that  of  the  parts  concerned  in  the  formation  of 
secretions.  And  since  the  differences  of  the  two  processes  of  separation, 
corresponding  with  tliose  in  tlie  several  purposes  and  destinations  of  tlie 
fluids,  are  not  yet  ascertained,  it  will  be  sufficient  to  speak  in  general 
terms  of  tlie  })roccss  of  separation  or  secretion. 

Every  secreting  apparatus  possesses,  as  essentijil  parts  of  its  structure, 
a  simple  and  almost  textureless  membrane,  named  the  primary  or  hase- 


SECKETION. 


ment-membrane;  certain  cells;  and  blood-vessels.  These  three  structural 
elements  are  arranged  together  in  various  ways;  but  all  the  varieties  may 
be  classed  under  one  or  other  of  two  principal  divisions,  namely,  mem- 
branes and  glands. 


Organs  akd  Tissues  of  Secretion". 

The  principal  secreting  membranes  are  (1)  the  Serous  and  Synovial 
membranes;  (2)  the  Mucous  membranes;  (3)  the  Mammary  gland;  (4) 
the  Lachrymal  gland;  and  (5)  the  Skin. 

(1)  Serous  Membranes. — The  serous  membranes  are  especially  dis- 
tinguished by  the  characters  of  the  endothelium  covering  their  free  sur- 


r 
I 


Fig.  219.— Section  of  synovial  membrane,  a,  endothelial  covering  of  elevations  of  the  membrane ; 
6,  subserous  tissue  containing  fat  and  blood-vessels;  c,  ligament  covered  by  the  synovial  membrane. 
(Cadiat.) 

face:  it  always  consists  of  a  single  layer  of  polygonal  cells.  The  ground 
substance  of  most  serous  membranes  consists  of  connective -tissue  cor- 
puscles of  various  forms  lying  in  the  branching  spaces  which  constitute 
the  **lymph  canalicular  system'^  (p.  292),  and  interwoven  with  bundles 
of  white  fibrous  tissue,  and  numerous  delicate  elastic  fibrillse,  together 
with  blood-vessels,  nerves,  and  lymphatics.  In  relation  to  the  process  of 
secretion,  the  layer  of  connective  tissue  serves  as  a  groundwork  for  the 
ramification  of  blood-vessels,  lymphatics,  and  nerves.  But  in  its  usual 
form  it  is  absent  in  some  instances,  as  in  the  arachnoid  covering  the 
dura  mater,  and  in  the  interior  of  the  ventricles  of  the  brain.  The 
primary  membrane  and  epithelium  are  always  present,  and  are  concerned 


o20  HAND-BOOK  OF  PHYSIOLOGY. 

in  the  formation  of  the  fluid  by  which  the  free  surface  of  tne  membrane 
is  moistened. 

Serous  membranes  are  of  two  principal  kinds:  l^^.  Those  which  line 
visceral  cavities, — the  aracluioid,  pericardium,  pleu)w,  peritoneum^  and 
tuniccB  vaginaJes.  '2nd.  The  synovial  membranes  lining  the  joints,  and 
the  sheaths  of  tendons  and  ligaments,  with  which,  also,  are  usually  in- 
cluded the  synovial  bur  see,  or  hirsce  mucosce,  whether  these  be  subcutane- 
ous, or  situated  beneath  tendons  that  glide  over  bones. 

The  serous  membranes  form  closed  sacs,  and  exist  wherever  the  free 
surfaces  of  viscera  come  into  contact  with  each  other  or  lie  in  cavities 
unattached  to  surrounding  parts.  The  viscera  invested  by  a  serous  mem- 
brane are,  as  it  were,  pressed  into  the  shut  sac  which  it  forms,  carrying 
before  them  a  portion  of  the  membrane,  which  serves  as  their  investment. 
To  the  law  that  serous  membranes  form  shut  sacs,  there  is,  in  the 
human  subject,  one  exception,  viz. :  the  opening  of  the  Fallopian  tubes 
into  the  abdominal  cavity, — an  arrangement  which  exists  in  man  and  all 
Vertebrata,  with  the  exception  of  a  few  fishes. 

Functions. — The  principal  purpose  of  the  serous  and  synovial  mem- 
branes is  to  furnish  a  smooth,  moist  surface,  to  facilitate  the  movements 
of  the  invested  organ,  and  to  prevent  the  injurious  etiects  of  friction. 
This  purpose  is  especially  manifested  in  joints,  in  which  free  and  exten- 
sive movements  take  place;  and  in  the  stomach  and  intestines,  which, 
from  the  varying  quantity  and  movements  of  their  contents,  are  in  almost 
constant  motion  upon  one  another  and  the  walls  of  the  abdomen. 

Serous  Fluid. — The  fluid  secreted  from  the  free  surface  of  the  serous 
membranes  is,  in  health,  rarely  more  than  sufficient  to  ensure  the  main- 
tenance of  their  moisture.  The  opposed  surfaces  of  each  serous  sac  are  at 
every  point  in  contact  with  each  other.  After  death,  a  larger  quantity 
of  fluid  is  usually  found  in  each  serous  sac;  but  this,  if  not  the  product 
of  manifest  disease,  is  probably  such  as  has  transuded  after  death,  or  in 
the  last  hours  of  life.  An  excess  of  such  fluid  in  any  of  the  serous  sacs 
constitutes  dropsy  of  the  sac. 

The  fluid  naturally  secreted  by  the  serous  membranes  appears  to  be 
identical,  in  general  and  chemical  characters,  with  the  serum  of  the 
blood,  or  with  very  dilute  liquor  saguinis.  It  is  of  a  pale  yellow  or  straw 
color,  slightly  viscid,  alkaline,  and,  on  account  of  the  presence  of  albu- 
men, coagulable  by  heat.  This  similarity  of  the  serous  fluid  to  the  liquid 
part  of  blood,  and  to  the  fluid  with  which  most  animal  tissues  are  moist- 
ened, renders  it  probable  that  it  is,  in  great  measure,  separated  by  simple 
transudation,  through  the  walls  of  the  blood-vessels.  The  probability  is 
increased  by  the  fact  that,  in  jaundice,  the  fluid  in  the  serous  sacs  is. 
equally  with  tlie  serum  of  the  blood,  colored  with  the  bile.  But  there  is 
reason  for  supposing  that  the  fluid  of  the  cerebral  ventricles  and  of  the 
arachnoid  sac  are  exceptions  to  this  rule;  for  they  differ  from  the  fluids 


SECRETION. 


321 


of  the  other  serous  sacs  not  only  in  being  pellucid,  colorless,  and  of  much 
less  specific  gravity,  but  in  that  they  seldom  receive  the  tinge  of  bile 
when  present  in  the  blood,  and  are  not  colored  by  madder,  or  other 
similar  substances  introduced  abundantly  into  the  blood. 

Synovial  Fluid:  Synovia. — It  is  also  probable  that  the  formation 
of  synovial  fluid  is  a  process  of  more  genuine  and  elaborate  secretion,  by 
means  of  the  epithelial  cells  on  the  surface  of  the  membrane,  and  espe- 
cially of  those  which  are  accumulated  on  the  edges  and  processes  of  the 
synovial  fringes;  for,  in  its  peculiar  density,  viscidity,  and  abundance  of 
albumin,  synovia  differs  alike  from  the  serum  of  blood  and  from  the  fluid 
of  any  of  the  serous  cavities. 

(2)  Mucous  Membranes. — The  mucoics  memhranes  line  all  those 
passages  by  which  internal  parts  communicate  with  the  exterior,  and  by 
which  either  matters  are  eliminated  from  the  body  or  foreign  substances 
taken  into  it.  They  are  soft  and  velvety,  and  extremely  vascular.  The 
external  surfaces  of  mucous  membranes  are  attached  to  various  other 
.tissues;  in  the  tongue,  for  example,  to  muscle;  on  cartilaginous  parts,  to 
perichondrium;  in  the  cells  of  the  ethmoid  bone,  in  the  frontal  and 
sphenoidal  sinuses,  as  well  as  in  the  tympanum,  to  periosteum;  in  the 
intestinal  canal,  it  is  connected  with  a  firm  submucous  membrane,  which 
on  its  exterior  gives  attachment  to  the  fibres  of  the  muscular  coat.  The 
mucous  membranes  line  certain  principal  tracts — Gastro-Pulmonary  and 
Genito-Urinary;  the  former  being  subdivided  into  the  Digestive  and 
Eespiratory  tracts.  1.  The  Digestive  tract  commences  in  the  cavity  of 
the  mouth,  from  which  prolongations  pass  into  the  ducts  of  the  salivary 
glands.  From  the  mouth  it  passes  through  the  fauces,  pharynx,  and 
oesophagus,  to  the  stomach,  and  is  thence  continued  along  the  whole  tract 
of  the  intestinal  canal  to  the  termination  of  the  rectum,  being  in  its 
course  arranged  in  the  various  folds  and  depressions  already  described,, 
and  prolonged  into  the  ducts  of  the  intestinal  glands,  the  pancreas  and 
liver,  and  into  the  gall-bladder.  2.  The  Respiratory  tract  includes  the 
mucous  membrane  lining  the  cavity  of  the  nose,  and  the  various  sinuses, 
communicating  with  it,  the  lachrymal  canal  and  sac,  the  conjunctiva  of 
the  eye  and  eyelids,  and  the  prolongation  which  passes  along  the  Eusta- 
chian tubes  and  lines  the  tympanum  and  the  inner  surface  of  the  mem- 
brana  tympani.  Crossing  the  pharynx,  and  lining  that  part  of  it  which 
is  above  the  soft  palate,  the  respiratory  tract  leads  into  the  glottis,  whence 
it  is  continued,  through  the  larynx  and  trachea,  to  the  bronchi  and  their 
divisions,  which  it  lines  as  far  as  the  branches  of  about  -^^  of  an  inch  in 
diameter,  and  continuous  with  it  is  a  layer  of  delicate  epithelial  mem- 
brane which  extends  into  the  pulmonary  cells.  3.  The  Genito-urinary 
tract,  which  lines  the  whole  of  the  urinary  passages,  from  their  external 
orifice  to  the  termination  of  the  tubuli  uriniferi  of  the  kidneys,  extends 
also  into  the  organs  of  generation  in  both  sexes,  and  into  the  ducts  of  the 
Vol.  I.— 21." 


322 


HAND-BOOK  OF  PHYSIOLOGY. 


glands  connected  with  them;  and  in  the  female  becomes  continuous  with 
the  serous  membrane  of  the  abdomen  at  the  fimbriae  of  the  Fallopian  tubes. 

Structure. — Along  each  of  the  above  tracts,  and  in  different  portions 
of  each  of  them,  the  mucous  membrane  presents  certain  structural  pecu- 
liarities adapted  to  the  functions  which  each  part  has  to  discharge;  yet  in 
some  essential  characters  mucous  membrane  is  the  same,  from  whatever 
part  it  is  obtained.  In  all  the  principal  and  larger  parts  of  the  several 
tracts,  it  presents,  as  just  remarked,  an  external  layer  of  epithelium,  sit- 
uated upon  'basement-memhrane,  and  beneath  this,  a  stratum  of  vascular 
tissue  of  variable  thickness,  containing  lymphatic  vessels  and  nerves 
which  in  different  cases  presents  either  outgrowths  in  the  form  of  papillae 
and  villi,  or  depressions  or  involutions  in  the  form  of  glands.  But  in  the 
prolongations  of  the  tracts,  where  they  pass  into  gland-ducts,  these  con- 
stituents are  reduced  in  the  finest  branches  of  the  ducts  to  the  epithelium, 
the  primary  or  basement-membrane,  and  the  capillary  blood-vessels 
spread  over  the  outer  surface  of  the  latter  in  a  single  layer. 

The  primary  or  basement-membrane  is  a  thin  transparent  layer, 
simple,  homogeneous,  or  composed  of  endothelial  cells.  In  the  minuter 
divisions  of  the  mucous  membranes,  and  in  the  ducts  of  glands,  it  is  the 
layer  continuous  and  correspondent  with  this  basement-membrane  that 
forms  tjie  proper  walls  of  the  tubes.  The  cells  also  which,  lining  the 
larger  and  coarser  mucous  membranes,  constitute  their  epithelium,  are 
continuous  with,  and,  often  similar  to  those  which,  lining  the  gland- 
ducts,  are  called  gland-cells,  l^o  certain  distinction  can  be  drawn  be- 
tw^een  the  epithelium-cells  of  mucous  membranes  and  gland-cells.  It  thus 
appears,  that  the  tissues  essential  to  the  production  of  a  secretion  are,  in 
their  simplest  form,  a  membrane,  having  on  one  surface  blood-vessels,  and 
on  the  other  a  layer  of  cells,  which  may  be  called  either  epithelium-cells 
or  gland-cells. 

Mucous  Fluid:  Mucus. — From  all  mucous  membranes  there  is 
secreted  either  from  the  surface  or  from  certain  special  glands,  or  from 
both,  a  more  or  less  viscid,  greyish,  or  semi-transparent  fluid,  of  alkaline 
reaction  and  high  specific  gravity,  named  mucus.  It  mixes  imperfectly 
with  water,  but,  rapidly  absorbing  liquid,  it  swells  considerably  when 
water  is  added.  Under  the  microscope  it  is  found  to  contain  epithelium 
and  leucoc3^tes.  It  is  found  to  be  made  up,  chemically,  of  a  nitrogenous 
principle  called  mucin  which  forms  its  chief  bulk,  of  a  little  albumen,  of 
salts  chiefly  chlorides  and  phosphates,  and  water  with  traces  of  fats  and 
extractives. 

Secreting  Glands. — The  structure  of  the  elementary  portions  of  a 
sccretiiig  apparatus,  namely  epithelium,  simple  membrane,  and  blood- 
vessels having  been  already  described  in  this  and  previous  chapters,  we 
may  proceed  to  consider  the  manner  in  which  they  are  arranged  to  form 
the  varieties  of  secreting  glands. 


SECRETION. 


323 


The  secreting  glands  are  the  organs  to  which  the  function  of  secretion 
is  more  especially  ascribed;  for  they  appear  to  be  occupied  with  it  alone. 
They  present,  amid  manifold  diversities  of  form  and  composition,  a  gen- 
eral plan  of  structure,  by  which  they  are  distinguished  from  all  other 
textures  of  the  body;  especially,  all  contain,  and  appear  constructed  with 
particular  regard  to,  the  arrangement  of  the  cells,  which,  as  already  ex- 
pressed, both  line  their  tubes  or  cavities  as  an  epithelium,  and  elaborate, 
as  secreting  cells,  the  substances  to  be  discharged  from  them.  Glands 
are  provided  also  with  lymphatic  vessels  and  nerves.  The  distribution  of 
the  formei  is  not  peculiar,  and  need  not  be  here  considered.  Nerve -fibres 
are  distributed  both  to  the  blood-vessels  of  the  gland  and  to  its  ducts; 
and,  in  some  glands,  to  the  secreting  cells  also  (p.  229). 

Varieties. — 1.  The  simple  tubule,  or  tuhular  gland,  (a.  Fig.  220), 
examples  of  which  are  furnished  by  some  mucous  glands,  the  follicles  of 
Lieberkiihn  (Fig.  186),  and  the  tubular  glands  of  the  stomach.  These 
appear  to  be  simple  tubular  depressions  of  the  mucous  membrane,  the 
wall  of  which  is  formed  of  primary  membrane,  and  is  lined  with  secreting 
cells  arranged  as  an  epithelium.  To  the  same  class  may  be  referred  the 
elongated  and  tortuous  sudoriferous  glands. 

The  compound  tubular  glands  (d.  Fig.  220)  form  another  division. 
These  consist  of  main  gland-tubes,  which  divide  and  subdivide.  Each 
gland  may  consist  of  the  subdivisions  of  one  or  more  main-tubes.  The 
ultimate  subdivisions  of  the  tubes  are  generally  highly  convoluted. 
They  are  formed  of  a  basement-membrane,  lined  by  epithelium  of  various 
forms.  The  larger  tubes  may  have  an  outside  coating  of  fibrous,  areolar, 
or  muscular  tissue.  The  kidney,  testis,  salivary  glands,  pancreas,  Brun- 
ner's  glands  with  the  lachrymal  and  mammeiry  glands,  and  some  mucous 
glands  are  examples  of  this  type,  but  present  more  or  less  marked  varia- 
tions among  themselves. 

2.  The  aggregate  or  racemose  glands,  in  which  a  number  of  vesicles  or 
acini  are  arranged  in  groups  or  lobules  (c.  Fig.  220).  The  Meibomian 
follicles  are  examples  of  this  kind  of  gland. 

These  various  organs  differ  from  each  other  only  in  secondary  points 
of  structure;  such  as,  chiefly,  the  arrangement  of  their  excretory  ducts, 
the  grouping  of  the  acini  and  lobules,  their  connection  by  areolar  tissue, 
and  supply  of  blood-vessels.  The  acini  commonly  appear  to  be  formed 
by  a  kind  of  fusion  of  the  walls  of  several  vesicles,  which  thus  combine 
to  form  one  cavity  lined  or  filled  with  secreting  cells  which  also  occupy 
recesses  from  the  main  cavity.  The  smallest  branches  of  the  gland-ducts 
sometimes  open  into  the  centres  of  these  cavities;  sometimes  the  acini 
are  clustered  round  the  extremities,  or  by  the  sides  of  the  ducts:  but, 
whatever  secondary  arrangement  there  may  be,  all  have  the  same  essen- 
tial character  of  rounded  groups  of  vesicles  containing  gland-cells,  and 
opening  by  a  common  central  cavity  into  minute  ducts,  which  ducts  in 


324 


HAND-BOOK  OF  PHYSIOLOGY. 


the  large  glands  converge  and  unite  to  form  larger  and  larger  branches, 
and  at  length  by  one  common  trunk,  open  on  a  free  surface  of  membrane. 

Among  these  varieties  of  structure,  all  the  secreting  glands  are  alike  in 
some  essential  points,  besides  those  which  they  have  in  common  with  all 
truly  secreting  structures.  They  agree  in  presenting  a  large  extent  of 
secreting  surface  within  a  comparatively  small  space;  in  the  circumstance 


Fig.  220. — Plans  of  extension  of  secreting  membrane  by  inversion  or  recession  in  form  of  cavities. 
A,  simple  glands,  viz.  gr,  straight  tube;  7i,  sac;  i,  coiled  tube.  B,  multilocular  crypts;  fc,  of  tubular 
form;  Z,  saccular.  C,  racemose,  or  saccular  compound  gland;  m,  entire  gland,  snowing  branched 
duct  and  lobular  structure;  ?!,  a  lobule,  detached  with  o,  branch  of  duct  proceeding  from  it.  D,  com- 
pound tubular  gland.  (Sharpey.) 

that  while  one  end  of  the  gland-duct  opens  on  a  free  surface,  the  opposite 
end  is  always  closed,  having  no  direct  communication  with  blood-vessels, 
or  any  other  canal;  and  in  a  uniform  arrangement  of  capillary  blood- 
vessels, ramifying  and  forming  a  network  around  the  walls  and  in  the 
interstices  of  the  ducts  and  acini. 

Process  of  Secretion. — In  secretion  two  distinct  processes  are  con- 
cerned which  may  be  spoken  of  as,  1.  Physicaly  and  2.  Chemicdl. 


SECRETION. 


325 


1.  Physical  processes. — These  are  such  as  can  be  closely  imitated  in 
the  laboratory,  inasmuch  as  they  consist  in  the  operation  of  well-known 
physical  laws:  they  are — 

(a)  Filtration,    {i)  Diffusion. 

{a)  Filtration  is  simply  the  passage  of  a  fluid  through  a  porous  mem- 
brane under  the  influence  of  pressure.  If  two  fluids  be  separated  by  a 
porous  membrane,  and  the  pressure  on  one  side  is  greater  than  on  the 
other,  it  is  evident  that  in  the  absence  of  counteracting  osmotic  influ- 
ences (see  below)  there  will  be  a  filtration  through  the  membrane  until 
the  pressure  on  the  two  sides  is  equalized.  Of  course  there  may  only 
be  fluid  on  one  side  of  the  membrane,  as,  in  the  ordinary  process  of  filter- 
ing through  blotting-paper,  and  then  the  filtration  will  continue  as  long 
as  the  pressure  (in  this  case,  the  weight  of  the  fluid)  is  sufficient  to  force 
it  through  the  pores  of  the  filter.  The  necessary  inequality  of  pressure 
may  be  obtained  either  by  diminishing  it  on  one  side,  as  in  the  case  of 
cupping;  or  increasing  it  on  the  other,  as  in  the  case  of  the  increased 
blood-pressure  and  consequent  increased  flow  of  urine  resulting  from 
copious  drinking.  By  filtration,  not  merely  water,  but  various  salts  in 
solution,  may  transude  from  the  blood-vessels.  It  seems  probable  that 
some  fluids,  such  as 'the  secretions  of  serous  membranes,  are  simply  exu- 
dations or  oozings  (filtration)  from  the  blood-vessels,  whose  qualities  are 
determined  by  those  of  the  liquor  sanguinis,  while  the  quantities  are  liable 
to  variation,  and  are  chiefly  dependent  upon  the  blood-pressure. 

(h)  Diffusion  is  the  passage  of  fluids  through  a  moist  animal  mem- 
brane independent  of  pressure,  and  sometimes  actually  in  opposition  to 
it.  There  must  always  be  in  this  process  two  fluids  differing  in  composi- 
tion, one  or  both  possessing  an  affinity  for  the  intervening  membrane, 
and  the  fluids  capable  of  being  mixed  one  with  the  other;  the  osmotic 
current  continuing  in  each  direction  (when  both  fluids  have  an  affinity 
for  the  membrane)  until  the  chemical  composition  of  the  fluid  on  each 
side  of  the  septum  becomes  the  same. 

2.  Chemical  processes. — These  constitute  the  process  of  secretion  prop- 
erly so  called  as  distinguished  from  mere  transudation  spoken  of  above. 
In  the  chemical  process  of  secretion  various  materials  which  do  not  exist 
as  such  in  the  blood  are  elaborated  by  the  agency  of  the  gland-cells  from 
the  blood,  or,  to  speak  more  accurately,  from  the  plasma  which  exudes 
from  the  blood-vessels  into  the  interstices  of  the  gland-textures. 

The  best  evidence  for  this  view  is:  1st.  That  cells  and  nuclei  are  con- 
stituents of  all  glands,  however  diverse  their  outer  forms  and  other  char- 
acters, and  are  in  all  glands  placed  on  the  surface  or  in  the  cavity  whence 
the  secretion  is  poured.  2nd,  That  many  secretions  which  are  visible 
with  the  microscope  may  be  seen  in  the  cells  of  their  glands  before  they 
are  discharged.  Thus,  bile  may  be  often  discerned  by  its  yellow  tinge  in 
the  gland-cells  of  the  liver;  spermatozoids  in  the  cells  of  the  tubules  of 


326 


HAND-BOOK  OF  PHYSIOLOGY. 


the  testicles;  granules  of  uric  acid  in  those  of  the  kidneys  (of  fish);  fatty 
particles,  like  those  of  milk,  in  the  cells  of  the  mammary  gland. 

Secreting  cells,  like  the  cells  or  other  elements  of  any  other  organ, 
appear  to  develop,  grow,  and  attain  their  individual  perfection  by  appro- 
priating nutriment  from  the  fluid  exuded  by  adjacent  blood-vessels  and 
elaborating  it,  so  that  it  shall  form  part  of  their  own  substance.  In  this 
perfected  state,  the  cells  subsist  for  some  brief  time,  and  when  that 
period  is  over  they  appear  to  dissolve,  wholly  or  in  part,  and  yield  their 
contents  to  the  peculiar  material  of  the  secretion.  And  this  appears  to  be 
the  case  in  every  part  oi  the  gl-and  that  contains  the  appropriate  gland- 
cells;  therefore  not  in  the  extremities  of  the  ducts  or  in  the  acini  alone, 
but  in  great  part  of  their  length. 

We  have  described  elsewhere  the  changes  which  have  been  noticed 
from  actual  experiment  in  the  cells  of  the  salivary  glands,  pancreas,  and 
peptic  gland  (pp.  235,  259,  265). 

Discharge  of  Secretions  from  glands  may  either  take  place  as  soon 
as  they  are  formed;  or  the  secretion  may  be  long  retained  within  the 
gland  or  its  ducts.  The  former  is  the  case  with  the  sweat  glands.  But 
the  secretions  of  those  glands  whose  activity  of  function  is  only  occa- 
sional are  usually  retained  in  the  cells  in  an  undeveloped  form  during  the 
periods  of  the  gland^s  inaction.  And  there  are  glands  which  are  like 
both  these  classes,  such  as  the  lachrymal,  which  constantly  secrete  small 
portions  of  fluid,  and  on  occasions  of  greater  excitement  discharge  it  more 
abundantly. 

When  discharged  into  the  ducts,  the  further  course  of  secretions  is 
affected  partly  by  the  pressure  from  behind;  the  fresh  quantities  of  secre- 
tion propelling  those  that  were  formed  before.  In  the  larger  ducts,  its 
propulsion  is  assisted  by  the  contraction  of  their  walls.  All  the  larger 
ducts,  such  as  the  ureter  and  common  bile-duct,  possess  in  their  coats 
plain  muscular  fibres;  they  contract  when  irritated,  and  sometimes  mani- 
fest peristaltic  movements.  Rhythmic  contractions  in  the  pancreatic  and 
bile-ducts  have  been  observed,  and  also  in  the  ureters  andvasa  deferentia. 
It  is  probable  that  the  contractile  power  extends  along  the  ducts  to  a  con- 
siderable distance  within  the  substance  of  the  glands  whose  secretions 
can  be  rapidly  expelled.  Saliva  and  milk,  for  instance,  are  sometimes 
ejected  with  much  force;  doubtless  by  the  energetic  and  simultaneous 
contraction  of  many  of  the  ducts  of  their  respective  glands. 

Circumstances  Influencing  Secretion. — Amongst  the  principal 
conditions  which  influence  secretion  are  (1)  variations  in  the  quantity  of 
blood,  (2)  in  the  quantity  of  the  peculiar  materials  for  any  secretion  that 
it  may  contain,  and  (3)  in  conditions  of  the  nerves  of  the  glands. 

(1.)  An  increase  in  the  qnavtity  of  Mood  traversing  a  glands  as  in 
nearly  all  the  instances  before  quoted,  coincides  generally  with  an  aug- 
mentation of  its  secretion.    Thus,  the  mucous  membrane  of  the  stomach 


SECRETION. 


327 


becomes  florid  when,  on  the  introduction  of  food,  its  glands  begin  to 
secrete;  the  mammary  gland  becomes  much  more  vascular  during  lacta- 
tion; and  all  circumstances  which  give  rise  to  an  increase  in  the  quantity 
of  material  secreted  by  an  organ  produce,  coincidently,  an  increased  sup- 
ply of  blood;  but  we  have  seen  that  a  discharge  of  saliva  may  occur  under 
extraordinary  circumstances,  without  increase  of  blood-supply  (p.  233), 
and  so  it  may  be  inferred  that  this  condition  of  increased  blood-supply 
is  not  absolutely  essential. 

(2.)  When  the  blood  contains  more  than  usual  of  the  materials  which 
the  glands  are  designed  to  separate  or  elaborate.  Thus,  when  an  excess 
of  nitrogenous  waste  is  in  the  blood,  whether  from  excessive  exercise,  or 
from  destruction  of  one  kidney,  a  healthy  kidney  will  excrete  more  urea 
than  it  did  before. 

(3.)  Influence  of  the  Nervous  System  07i  Secretio7i. — The  process  of 
secretion  is  largely  influenced  by  the  condition  of  the  nervous  system. 
The  exact  mode  in  which  the  influence  is  exhibited  must  still  be  regarded 
as  somewhat  obscure.  In  part,  it  exerts  its  inflaence  by  increasing  or 
diminishing  the  quantity  of  blood  supplied  to  the  secreting  gland,  in  vir- 
tue of  the  power  which  it  exercises  over  the  contractility  of  the  smaller 
blood-vessels;  while  it  also  has  a  more  direct  influence,  as  was  demon- 
strated  at  length  in  the  case  of  the  submaxillary  gland,  upon  the  secreting 
cells  themselves;  this  may  be  called  trophic  influence.  Its  influence  over 
secretion,  as  well  as  over  other  functions  of  the  body,  may  be  excited  by 
causes  acting  directly  upon  the  nervous  centres,  upon  the  nerves  going 
to  the  secreting  organ,  or  upon  the  nerves  of  other  parts.  In  the  latter 
case,  a  reflex  action  is  produced:  thus  the  impression  produced  upon  the 
nervous  centres  by  the  contact  of  food  in  the  mouth,  is  reflected  upon 
the  nerves  supplying  the  salivary  glands,  and  produces,  through  these,  a 
more  abundant  secretion  of  saliva  (p.  232). 

Through  the  nerves,  various  conditions  of  the  brain  also  influence  the 
secretions.  Thus,  the  thought  of  food  may  be  sufficient  to  excite  an 
abundant  flow  of  saliva.  And,  probably,  it  is  the  mental  state  which  ex- 
cites the  abundant  secretion  of  urine  in  hysterical  paroxysms,  as  well  as 
the  perspirations  and,  occasionally,  diarrhoea,  which  ensue  under  the  influ- 
ence of  terror,  and  the  tears  excited  by  sorrow  or  excess  of  joy.  The  qual- 
ity of  a  secretion  may  also  be  affected  by  the  mind;  as  in  the  cases  in  which, 
through  grief  or  passion,  the  secretion  of  milk  is  altered,  and  is  sometimes 
so  changed  as  to  produce  irritation  in  the  alimentary  canal  of  the  child, 
or  even  death  (Carpenter). 

Relations  between  the  Secretions. — The  secretions  of  some  of 
the  glands  seem  to  bear  a  certain  relation  or  antagonism  to  each  other, 
by  which  an  increased  activity  of  one  is  usually  followed  by  diminished 
activity  of  one  or  more  of  the  others;  and  a  deranged  condition  of  one  is 
apt  to  entail  a  disordered  state  in  the  others.    Such  relations  appear  to 


328 


HAND-BOOK  OF  PHYSIOLOGY. 


exist  among  the  various  mucous  membranes;  and  the  close  relation  be- 
tween the  secretion  of  the  kidney  and  that  of  the  skin  is  a  subject  of  con- 
stant observation. 

The  Mammary  Glakds  and  their  Secretion: — Milk. 

Structure. — The  mammary  glands  are  composed  of  large  divisions  or 
lobes,  and  these  are  again  divisible  into  lobules, — the  lobules  being  com- 
posed of  the  convoluted  subdivision  of  ducts  (alveoli).  The  lobes  and 
lobules  are  bound  together  by  areolar  tissue;  penetrating  between  the 
lobes,  and  covering  the  general  surface  of  the  gland,  with  the  exception 
of  the  nipple,  is  a  considerable  quantity  of  yellow  fat,  itself  lobulated  by 


locuii  of  the  connective-tissue  in  which  the  glandular  lobules  are  placed:  1.  upper  part  of  the  maniilla 
or  nipple:  2.  areola:  3,  subcutaneous  masses  of  fat;  4,  reticular  locuii  of  the  connective-tissue  which 
support  the  glandular  substance  and  contain  the  fatty  masses ;  5.  one  of  three  lactiferous  ducts  shown 
passing  toward  the  mamlUa  where  they  open:  6,  one  of  the  sinus  lactei  or  reservoirs:  7,  some  of  the 
glandular  lobules  which  have  been  unraveled;  7',  others  massed  together.  (Lusclika.) 

sheaths  and  processes  of  tough  areolar  tissue  (Fig.  221)  connected  both 
with  the  skin  in  front  and  the  gland  behind;  the  same  bond  of  connection 
extending  also  from  the  under  surface  of  the  gland  to  the  sheathing 
connective  tissue  of  the  great  pectoral  muscle  on  which  it  lies.  The  main 
ducts  of  the  gland,  fifteen  to  twenty  in  number,  called  the  lactiferous  or 
galadopliorous  ducts,  are  formed  by  the  union  of  the  smaller  (lobular) 
ducts,  and  open  by  small  separate  orifices  through  the  nipple.  At  the 
points  of  junction  of  lobular  ducts  to  form  lactiferous  ducts,  and  just  be- 
fore these  enter  the  base  of  the  nipple,  the  ducts  are  dilated  ((I,  Fig.  221); 


SECRETION. 


329 


and,  during  lactation,  the  period  of  active  secretion  by  the  gland,  the 
dilatations  form  reservoirs  for  the  milk,  which  collects  in  them  and  dis- 
tends them.  The  walls  of  the  gland-ducts  are  formed  of  areolar  and  elas- 
tic with  some  muscular  tissue,  and  are  lined  internally  by  short  columnar 
and  near  the  nipple  by  squamous  epithelium.  The  alveoli  consist  of  a 
membrana  propria  of  flattened  endothelial  cells  lined  by  low  columnar 
epithelium,  and  are  filled  with  fat  globules. 

The  nipple,  which  contains  the  terminations  of  the  lactiferous  ducts, 
is  composed  also  of  areolar  tissue,  and  contains  unstriped  muscular 
fibres.  Blood-vessels  are  also  freely  supplied  to  it,  so  as  to  give  it  a  species 
of  erectile  structure.  On  its  surface  are  very  sensitive  papillae;  and 
around  it  is  a  small  area  or  areola  of  pink  or  dark-tinted  skin,  on  which 
are  to  be  seen  small  projections  formed  by  minute  secreting  glands. 

Blood-vessels,  nerves,  and  lymphatics  are  plentifully  supplied  to  the 
mammary  glands;  the  calibre  of  the  blood-vessels,  as  well  as  the  size  of 
the  glands,  varying  very  greatly  under  certain  conditions,  especially  those 
of  pregnancy  and  lactation. 

Changes  in  the  Glands  at  certain  Periods.— The  minute 
changes  which  occur  in  the  mammary  gland  during  its  periods  of  evolu- 


FiG.  222.— Section  of  mammary  gland  of  rabbit  near  the  end  of  pregnancy,  showing  six  acini,  e, 
epithelial  cells  of  a  polyhedral  or  short  columnar  form,  with  which  the  acini  are  packed.  X  200. 
(Schofield.) 

tion  (pregnancy),  and  involution  (when  lactation  has  ceased),  are  the  fol- 
lowing:— 

The  most  favorable  period  for  observing  the  epithelium  of  the  mam- 
mary gland  fully  developed  is  shortly  before  the  end  of  pregnancy.  At 
this  period  the  acini  which  form  the  lobules  of  the  gland,  are  found  to 
be  lined  with  a  mosaic  of  polyhedral  epithelial  cells  (Fig.  222),  and  sup- 
ported by  a  connective  tissue  stroma. 

The  rapid  formation  of  milk  during  lactation  results  from  a  fatty 
metamorphosis  of  the  epithelial  cells:  "The  secretion  may  be  said  to  be 
produced  by  a  transformation  of  the  substance  of  successive  generations 


830 


HAND-BOOK  OF  PHYSIOLOGY. 


of  epithelial  cells,  and  in  the  state  of  full  activity  this  transformation  is 
so  complete  that  it  may  be  called  a  deliquescence'"  (Creighton). 

In  the  earlier  days  of  lactation,  epithelial  cells  partially  transformed 
are  discharged  in  the  secretion:  these  are  termed  "colostrum  corpuscles,"' 
but  later  on  the  cells  are  completely  transformed  before  the  secretion  is 
discharged. 

After  the  end  of  lactation,  the  mamma  gradually  returns  to  its  original 
size  {involution).  The  acini,  in  the  early  stages  of  involution,  are  lined 
with  cells  in  all  degrees  of  vacuolation  (Fig.  223).  As  involution  proceeds 
the  acini  diminish  considerably  in  size,  and  at  length,  instead  of  a  mosaic 
of  lining  epithelial  cells  (twenty  to  thirty  in  each  acinus),  we  have  five  or  six 
nuclei  ( some  with  no  surrounding  protoplasm)  lying  in  an  irregular  heap 


Fig.  223.— Section  of  mammary  gland  of  ewe  shortly  after  the  end  of  lactation,  showing  parts  of 
fom*  acini,  which  contain  numerous  epithelial  cells  undergoing  vacuolation  in  situ;  they  very  closely 
resemble  yoimg  fat-cells,  and  are  in  fact  just  like  "  Colostrum  corpuscles.'"   X  300.  (Creighton.) 


within  the  acinus.  During  the  later  stages  of  involution,  large  yellow 
granular  cells  are  to  be  seen.  As  the  acini  diminish  in  size,  the  con- 
nective tissue  and  fatty  matter  between  them  increase,  and  in  some  ani- 
mals, when  the  gland  is  completely  inactive,  it  is  found  to  consist  of  a 
thin  film  of  glandular  tissue  overlying  a  thick  cushion  of  fat.  Many  of 
the  products  of  waste  are  carried  off  by  the  lymphatics. 

During  pregnancy  the  mammary  glands  undergo  changes  {evolution) 
which  are  readily  observable.  They  enlarge,  become  harder  and  more 
distinctly  lobulated:  the  veins  on  the  surface  become  more  prominent. 
The  areola  becomes  enlarged  and  dusky,  with  projecting  papillae;  the 
nipple  too  becomes  more  prominent,  and  milk  can  be  squeezed'  from  the 
orifices  of  the  ducts.  This  is  a  very  gradual  process,  which  commences 
about  the  time  of  conception,  and  i)rogresses  steadily  during  the  whole 
period  of  gestation.  The  acini  enlarge,  and  a  series  of  changes  occur, 
exactly  the  reverse  of  those  just  described  under  the  head  of  Involu- 
tion. 


SECEETION. 


331 


The  Mammaey  Seceetiok: — Milk. 

Under  the  microscope,  milk  is  found  to  contain  a  number  of  globules 
of  various  sizes  (Fig.  224),  the  majority  about  xo  o-oir  ""^^h  in  diam- 

eter. They  are  composed  of  oily  matter,  probably  coated  by  a  fine  layer 
of  albuminous  material,  and  are  called  milk-globules;  while,  accompany- 
ing these,  are  numerous  minute  particles,  both  oily  and  albuminous, 
which  exhibit  ordinary  molecular  movements.  The  milk  which  is 
secreted  in  the  first  few  days  after  parturition,  and  which  is  called  the 
colostrum,  differs  from  ordinary  milk  in  containing  a  larger  quantity  of 
solid  matter;  and  under  the  microscope  are  to  be  seen  certain  granular 


masses  called  colostrum- corpuscles.  These,  which  appear  to  be  small 
masses  of  albuminous  and  oily  matter,  are  probably  secreting  cells  of  the 
gland,  either  in  a  state  of  fatty  degeneration,  or  old  cells  which  in  their 
attempt  at  secretion  under  the  new  circumstances  of  active  need  of  milk, 
are  filled  with  oily  matter;  which,  however,  being  unable  to  discharge, 
they  are  themselves  shed  bodily  to  make  room  for  their  successors.  Colos- 
trum-corpuscles have  been  seen  to  exhibit  contractile  movements  and 
to  squeeze  out  drops  of  oil  from  their  interior  (Strieker). 

Chemical  Composition. — Milk  is  in  reality  an  emulsion  consisting 
of  numberless  little  globules  of  fat,  coated  with  a  thin  layer  of  albumi- 
nous matter,  floating  in  a  large  quantity  of  water  which  contains  in  solu- 
tion casein,  serum-albumin,  milk-sugar  (lactose),  and  several  salts.  Its 
percentage  composition  has  been  already  mentioned,  but  may  be  here 
repeated.    Its  reaction  is  alkaline:  its  specific  gravity  about  1030. 


332 


HAND-BOOK  OF  PHYSIOLOGY. 


Table  of  the  Chemical  Composition  of  Milk. 


Huni3;D, 

Cows. 

Water  

890 

.  858 

Solids  

110 

.  142 

1000 

1000 

Proteids,  including  Casein  and 

Serum-Albumin 

35 

.  68 

Fats  or  Butter  .       .       .  . 

25 

.  38 

Sugar  (with  extractives)  . 

48 

.  30 

Salts 

2 

6 

110 

142 

When  milk  is  allowed  to  stand,  the  fat  globules,  being  the  lightest 
portion,  rise  to  the  top,  forming  cream.  If  a  little  acetic  acid  be  added 
to  a  drop  of  milk  under  the  microscope,  the  albuminous  j&lm  coating  the 
oil  drops  is  dissolved,  and  they  run  together  into  larger  drops.  The  same 
result  is  produced  by  the  process  of  churning,  the  effect  of  which  is  to 
break  up  the  albuminous  coating  of  the  oil  drops:  they  then  coalesce  to 
form  hutter. 

Curdling"  of  Milk. — If  milk  be  allowed' to  stand  for  some  time,  its 
reaction  becomes  acid:  in  popular  language  it  "turns  sour.^"  This  change 
appears  to  be  due  to  the  conversion  of  the  milk-sugar  into  lactic  acid, 
which  causes  the  precipitation  of  the  casein  (curdling):  the  curd  con- 
tains the  fat  globules:  the  remaining  fluid  (whey)  consists  of  water  hold- 
ing in  solution  albumin,  milk-sugar  and  certain  salts.  The  same  effect 
is  produced  in  the  manufacture  of  cheese,  which  is  really  casein  coagu- 
lated by  the  agency  of  rennet  (p.  248).  When  milk  is  boiled,  a  scum  of 
serum-albumin  forms  on  the  surface. 

Curdling  Ferments. — The  effect  of  the  ferments  of  the  gastric,  pan- 
creatic, and  intestinal  juices  in  curdling  milk  (curdling  ferments)  has 
already  been  mentioned  in  the  Chapter  on  Digestion. 

The  salts  of  milk  are  chlorides,  sulphates,  phosphates,  and  carbonates 
of  potassium,  sodium,  calcium. 


CHAPTEE  XII. 


THE  SKIN  AND  ITS  FUNCTIONS. 

The  skin  serves — (1),  as  an  external  integument  for  the  protection  of 
the  deeper  tissues,  and  (2),  as  a  sensitive  organ  in  the  exercise  of  touch; 
it  is  also  (3),  an  important  excretory,  and  (4),  an  absorbing  organ;  while 
it  plays  an  important  part  in  (5)  the  regulation  of  the  temperature  of  the 
body. 

Structure  of  the  Skin. — The  skin  consists,  principally,  of  .a  vascu- 
lar tissue,  named  the  coritwi,  derma,  or  cutis  vera,  and  an  external  cover- 
ing of  epithelium  termed  the  cuticle  or  epidermis.  Within  and  beneath 
the  corium  are  imbedded  several  organs  with  special  function,  namely 
sudoriferous  glands,  sebaceous  glands,  and  liair  follicles;  and  on  its  surface 
are  sensitive  papiJlce.  The  so-called  appendages  of  the  skin — the  hair  and 
nails — are  modifications  of  the  epidermis. 

Epidermis. — The  epidermis  is  composed  of  several  strata  of  cells  of  . 
various  shapes,  and  closely  resembles  in  its  structure  that  which  lines  the 
mouth.  The  following  four  layers  may  be  distinguished.  1.  Stratum 
corneum  (Fig.  225,  a),  consisting  of  many  superposed  layers  of  horny 
scales.  The  different  thickness  of  the  epidermis  in  different  regions  of 
the  body  is  chiefly  due  to  variations  in  the  thickness  of  this  layer;  e.g., 
on  the  horny  parts  of  the  palms  of  the  hands  and  soles  of  the  feet  it  is  of 
great  thickness.  The  stratum  corneum  of  the  buccal  epithelium  chiefly 
differs  from  that  of  the  epidermis  in  the  fact  that  nuclei  are  to  be  dis- 
tinguished in  'some  of  the  cells  even  of  its  most  superficial  layers. 

2.  Stratum  lucidum,  a  bright  homogeneous  membrane  consisting  of 
squamous  cells  closely  arranged,  in  some  of  which  a  nucleus  can  be  seen. 

3.  Stratum  granulosum,  consisting  of  one  layer  of  flattened  cells  which 
appear  fusiform  in  vertical  section:  they  are  distinctly  nucleated,  and  a 
number  of  granules  extend  from  the  nucleus  to  the  margins  of  the  cell. 

4.  Stratum  Malpigliii  or  Rete  mucosum,  which  consists  of  many  strata. 
The  deepest  cells,  placed  immediately  above  the  cutis  vera,  are  columnar 
with  oval  nuclei:  this  layer  of  columnar  cells  is  succeeded  by  a  number 
of  layers  of  more  or  less  polyhedral  cells  with  spherical  nuclei;  the  cells 
of  the  more  superficial  layers  are  considerably  flattened.  The  deeper  sur- 
face of  the  rete  mucosum  is  accurately  adapted  to  the  papillae  of  the 
true  skin,  being,  as  it  were,  moulded  on  them.  It  is  very  constant  in 
thickness  in  all  parts  of  the  skin.    The  cells  of  the  middle  layers  of  the 


334 


HAND-BOOK  OF  PHYSIOLOGY. 


stratum  Malpighii  are  almost  all  connected  by  processes,  and  thus  form 
"prickle  cells"  (p.  21).  The  pigment  of  the  skin,  the  varying  quantity 
of  which  causes  the  various  tints  observed  in  different  individuals  and 
different  races,  is  contained  in  the  dee]3er  cells  of  the  rete  mucosum;  the 
pigmented  cells  as  they  approach  the  free  surface  gradually  losing  their 
color.  Epidermis  maintains  its  thickness  in  spite  of  the  constant  wear 
and  tear  to  which  it  is  subjected.  The  columnar  cells  of  the  deepest 
layer  of  the  "rete  mucosum"  elongate,  and  their  nuclei  divide  into  two 


Fig.  225.— Vertical  section  of  the  epidermis  of  the  prepuce,  a,  stratum  cornevmi,  of  verj'  few 
layers,  the  stratum  lucidmn  and  stratum  granulosum  not  being  distinctly  represented;  b.  c,  d,  and  e. 
the  layers  of  the  stratum  Malpighii,  a  certain  nxmiber  of  the  cells  in  layers  d  and  e  showing  signs  of 
segmentation;  layer  c  consists  chieflj'  of  prickle  or  ridge  and  furrow  cells;  /,  basement  membrane; 
cells  in  cutis  vera.  (Cadiat.) 

Fig.  226.— Vertical  section  of  skin  of  the  negro,  a,  a.  Cutaneous  papillae.  •  ft.  Undermost  and 
dark-colored  laj-er  of  oblong  vertical  epidermis-ceUs.  c.  Stratum  Malpighii.  d.  Superficial  layers, 
including  stratum  corneum.  stratum  lucidum,  and  stratimi  granulosum,  the  last  two  not  differen- 
tiated in  flgm-e.    X  250.  (Sharpey.) 

(Fig.  225,  e).  Lastly  the  upper  part  of  the  cell  divides  from  the  lower; 
thus  from  a  long  columnar  cell  are  produced  a  polyhedral  and  a  shortj 
columnar  cell:  the  latter  elongates  and  the  process  is  repeated.  The' 
polyhedral  cells  thus  formed  are  pushed  up  toward  the  free  surface  by  the 
production  of  fresh  ones  beneath  them,  and  become  flattened  from  pres- 
sure: they  also  become  gradually  horny  by  evaporation  and  transforma- 
tion of  their  protoplasm  into  keratin,  till  at  last  by  rubbing  they  are 
detached  as  dry  horny  scales  at  the  free  surface.  There  is  thus  a  con- 
stant production  of  fresh  cells  in  the  deeper  layers,  and  a  constant  throw- 
ing off  of  old  ones  from  the  free  surface.  When  these  two  processes  are 
accurately  balanced,  the  epidermis  maintains  its  thickness.    When,  by 


THE  SKIN  AND  ITS  FUNCTIONS. 


335 


intermittent  pressure,  a  more  active  cell-growth  is  stimulated,  the  produc- 
tion of  cells  exceeds  their  waste  and  the  epidermis  increases  in  thickness, 
as  we  see  in  the  horny  hands  of  the  laborer. 

The  thickness  of  the  epidermis  on  different  portions  of  the  skin  is 
directly  proportioned  to  the  friction,  pressure,  and  other  sources  of  injury 
to  which  it  is  exposed;  for  it  serves  as  well  to  protect  the  sensitive  and 
vascular  cutis  from  injury  from  without,  as  to  limit  the  evaporation  of 
fluid  from  the  blood-vessels.  The  adaptation  of  the  epidermis  to  the 
latter  purposes  may  be  well  shown  by  exposing  to  the  air  two  dead  hands 
or  feet,  of  which  one  has  its  epidermis  perfect,  and  the  other  is  deprived 
of  it;  in  a  day,  the  skin  of  the  latter  will  become  brown,  dry,  and  horn- 
like, while  that  of  the  former  will  almost  retain  its  natural  moisture. 

Cutis  vera. — The  corium  or  cutis,  which  rests  upon  a  layer  of  adi- 
pose and  cellular  tissue  of  varying  thickness,  is  a  dense  and  tough,  but 
yielding  and  highly  elastic  structure,  composed  of  fasciculi  of  fibro- 
cellular  tissue,  interwoven  in  all  directions,  and  forming,  by  their  inter- 
lacements, numerous  spaces  or  areolae.  These  areolae  are  large  in  the 
deeper  layers  of  the  cutis,  and  are  there  usually  filled  with  little  masses 
of  fat  (Fig.  228) :  but,  in  the  superficial  parts,  they  are  small  or  entirely 
obliterated.    Plain  muscular  fibre  is  also  abundantly  present. 

Papillae. — The  pai^illae  are  conical  elevations  of  the  cutis  vera,  with  a 
single  or  divided  free  extremity,  more  prominent  and  more  densely  set  at 
some  parts  than  at  others  (Figs.  227  and  230).  The  parts  on  which  they 
are  most  abundant  and  most  prominent,  are  the  palmar  surface  of  the 


Fig.  227.— Compound  papillae  from  the  palm  of  the  hand;  a,  basis  of  a  papilla;  6,  6,  divisions  or 
branches  of  the  same;  c,  c.  branches  belonging  to  papiUae,  of  which  the  bases  are  hidden  from  view. 
X  60.  (KoUiker.) 

hands  and  fingers,  and  the  soles  of  the  feet — parts,  therefore,  in  w^hich 
the  sense  of  touch  is  most  acute.  On  these  parts  they  are  disposed  in 
double  rows,  in  parallel  curved  lines,  separated  from  each  other  by 
depressions.  Thus  they  may  be  seen  easily  on  the  palm,  whereon  each 
raised  line  is  composed  of  a  double  row  of  papillae,  and  is  intersected  by 
short  transverse  lines  or  furrows  corresponding  with  the  interspaces 
between  the  successive  pairs  of  papillae.  Over  other  parts  of  the  skin 
they  are  more  or  less  thinly  scattered,  and  are  scarcely  elevated  above  the 
surface.    Their  average  length  is  about       of  an  inch,  and  at  their  base 


336 


HAND-BOOK  OF  PHYSIOLOGY. 


they  measure  about  -^^-^  of  an  inch  in  diameter.  Each  papilla  is  abun-. 
dantly  supplied  with  blood,  receiving  from  the  vascular  plexus  in  the 
cutis  one  or  more  minute  arterial  twigs,  which  divide  into  capillary  loops 
in  its  substance,  and  then  reunite  into  a  minute  vein,  which  passes  out  at 
its  base.  The  abundant  supply  of  blood  which  the  papillae  thus  receive 
explains  the  turgescence  or  kind  of  erection  which  they  undergo  when 
the  circulation  through  the  skin  is  active.    The  majority,  but  not  all,  of 


Fig.  228.— Vertical  section  of  skin.  A.  Sebaceous  gland  opening  into  halMOllicle.  B.  Muscular 
fibres.  C.  Sudoriferous  or  sweat-gland.  D.  Subcutaneous  fat.  E.  Fundus  of  hair-foUicle,  with  hair- 
papUIae.   (Klein  and  Noble  Smith.) 

the  papillae  contain  also  one  or  more  terminal  nerve-fibres,  from  the 
ultimate  ramifications  of  the  cutaneous  plexus,  on  which  their  exquisite 
sensibility  depends. 

Nerve-terminations. — In  some  parts,  especially  those  in  which  the 
sense  of  touch  is  highly  developed,  as,  for  example,  the  palm  of  the  hand 
and  the  lips,  the  nerve-fibres  appear  to  terminate,  in  many  of  the  papillae, 
by  one  or  more  free  ends  in  the  substance  of  an  oval-shaped  body,  occupy- 
ing the  principal  part  of  the  interior  of  the  papillte,  and  termed  a  touch- 


THE  SKIN  AND  ITS  FUNCTIONS. 


337 


corpuscle  (Fig.  229).  The  nature  of  this  body  is  obscure.  Some  regard  it 
as  little  else  than  a  mass  of  fibrous  or  connective  tissue,  surrounded  by 
elastic  fibres,  and  formed,  according  to  Huxley,  by  an  increased  develop- 
ment of  the  primitive  sheaths  of  the  nerve-fibres,  entering  the  papillae. 
Others,  however,  believe  that,  instead  of  thus  consisting  of  a  homogeneous 
mass  of  connective  tissue,  they  are  special  and  peculiar  bodies  of  lami- 
nated structure,  directly  concerned  in  the  sense  of  touch.  They  do  not 
occur  in  all  the  papillse  of  the  parts  where  they  are  found,  and,  as  a  rule, 
in  the  papillse  in  which  they  are  present  there  are  no  blood-vessels.  Since 


Fig.  229.— Papillse  from  the  skin  of  the  hand,  freed  from  the  cuticle  and  exhibiting  tactile  cor- 
puscles. A.  Simple  papilla  with  four  nerve-fibres:  a,  tactile  corpuscles;  6,  nerves,  b.  Papilla  treated 
with  acetic  acid;  a,  cortical  layer  with  cells  and  fine  elastic  filaments;  ft,  tactile  corpuscle  with  trans- 
verse nuclei;  c,  entering  nerve  with  neurilemma  or  perineurium;  d,  nerve-fibres  winding  roimd  the 
corpuscle,  c.  PapiUa  viewed  from  above  so  as  to  appear  as  a  cross-section:  a,  cortical  layer;  6,  nerve- 
fibre;  c,  sheath  of  the  tactile  corpuscle  containing  nuclei;  cZ,  core.    X  350.  (KoUiker.) 

these  peculiar  bodies  in  which  the  nerve-fibres  end  are  only  met  with  in 
the  papillae  of  highly  sensitive  parts,  it  may  be  inferred  that  they  are 
specially  concerned  in  the  sense  of  touch,  yet  their  absence  from  the 
papillae  of  other  tactile  parts  shows  that  they  are  not  essential  to  this 
sense. 

Closely  allied  in  structure  to  the  touch-corpuscles,  are  some  little  bodies 
called  end-buTbs,  about  inch  in  diameter  (Krause).  They  are  gener- 
ally oval  or  spheroidal,  and  composed  externally  of  a  coat  of  connective 
tissue  enclosing  a  softer  matter,  in  which  the  extremity  of  a  nerve  termi- 
nates. These  bodies  have  been  found  chiefly  in  the  lips,  tongue,  palate^ 
and  the  skin  of  the  glans  penis  (Fig.  230). 

Glands  of  the  Skin. — The  skin  possesses  glands  of  two  kinds:  (ol) 
Sudoriferous,  or  Sweat  Glands;  (^)  Sebaceous  Glands. 

[a)  Sudoriferous,  or  Sweat  Glands. — Each  of  these  glands  consists  of  a, 
small  lobular  mass,  formed  of  a  coil  of  tubular  gland-duct,  surrounded, 
by  blood-vessels  and  embedded  in  the  subcutaneous  adipose  tissue  (Fig. 
228,  c).  From  this  mass,  the  duct  ascends,  for  a  short  distance,  in  a 
spiral  manner  through  the  deeper  part  of  the  cutis,  then  passing  straight. 
Vol.  I.— 22. 


338 


HAND-BOOK  OF  PHYSIOLOGY. 


and  then  sometimes  again  becoming  spiral,  it  passes  through  the  cuticle 
and  opens  by  an  oblique  valve-like  aperture.  In  the  parts  where  the  epi- 
dermis is  thin  the  ducts  themselves  are  thinner  and  more  nearly  straight 
in  their  course  (Fig.  228).  The  duct,  which  maintains  nearly  the  same 
diameter  throughout,  is  lined  with  a  layer  of  columnar  epithelium  (Fig. 


Fig.  230.— End-bulbs  in  papillae  (magnified)  treated  with  acetic  acid,  a,  from  the  lips:  the  white 
loops  in  one  of  them  are  capillaries,  b,  from  the  tongue.  Two  end-bulbs  seen  in  the  midst  of  the 
simple  papillae:  a,  a,  nerves.  (Kolliker.) 


231)  continuous  with  the  epidermis;  while  the  part  which  passes  through 
the  epidermis  is  composed  of  the  latter  structure  only;  the  cells  which 
immediately  form  the  boundary  of  the  canal  in  this  part  being  somewhat 
differently  arranged  from  those  of  the  adjacent  cuticle. 


Fig.  231.— Glomeruli  of  sudoriferous  gland,  divided  in  various  directions,  a,  sheath  of  the  gland; 
6,  columnar  epithelial  lining  of  gland  tube;  c,  lumen  of  tube;  d,  divided  blood-vessel*  ■'loose-con- 
nective-tissue, forming  a  capsule  to  the  gland.  (Biesiadecki.) 


The  sudoriferous  glands  are  abundantly  distributed  over  the  whole  sur- 
face of  the  body;  but  are  especially  numerous,  as  well  as  very  large,  in 
the  skin  of  the  palm  of  tlio  hand,  and  of  the  sole  of  the  foot.    The  glands 


THE  SKIN  AND  ITS  FUNCTIONS. 


339 


by  which  the  peculiar  odorous  matter  of  the  axillae  is  secreted  form  a 
nearly  complete  layer  under  the  cutis,  and  are  like  the  ordinary  sudorifer- 
ous glands,  except  in  being  larger  and  having  very  short  ducts. 

The  peculiar  bitter  yellow  substance  secreted  by  the  skin  of  the  exter- 
nal auditory  passage  is  named  cerumen,  and  the  glands  themselves  ceru- 
minous  glands;  but  they  do  not  much  differ  in  structure  from  the  ordi- 
nary sudoriferous  glands. 

(h)  Seiaceous  Glands. — The  sebaceous  glands  (Fig.  232),  like  the  sudo- 
riferous glands,  are  abundantly  distributed  over  most  parts  of  the  body. 
They  are  most  numerous  in  parts  largely  supplied  with  hair,  as  the  scalp 


Fig.  232.— Sebaceous  gland  from  human  skin.  (Klein  and  Noble  Smith.) 

and  face,  and  are  thickly  distributed  about  the  entrances  of  the  various 
passages  into  the  body,  as  the  anus,  nose,  lips,  and  external  ear.  They 
are  entirely  absent  from  the  palmar  surface  of  the  hand  and  the  plantar 
surfaces  of  the  feet.  They  are  minutely  lobulated  glands  composed  of  an 
aggregate  of  small  tubes  or  sacculi  filled  with  opaque  white  substances, 
like  soft  ointment.  Minute  capillary  vessels  overspread  them;  and  their 
ducts  open  either  on  the  surface  of  the  skin,  close  to  a  hair,  or,  which  is 
more  usual,  directly  into  the  follicle  of  the  hair.  In  the  latter  case,  there 
are  generally  two  or  more  glands  to  each  hair  (Fig.  228). 

Hair. — A  hair  is  produced  by  a  peculiar  growth  and  modification  of 
the  epidermis.  Externally  it  is  covered  by  a  layer  of  fine  scales  closely 
imbricated,  or  overlapping  like  the  tiles  of  a  house,  but  with  the  free 


MO 


HAND-BOOK  OF  PHYSIOLOGY. 


edges  turned  upward  (Fig.  233,  a).  It  is  called  the  cuticle  of  the  hair. 
Beneath  this  is  a  much  thicker  layer  of  elongated  horny  cells,  closely 
packed  together  so  as  to  resemble  a  fibrous  structure.     This,  very  com- 


FiG.  233.— Surface  of  a  white  hair,  magnified  160  diameters.  The  wave  lines  mark  the  upper  or 
free  edges  of  the  cortical  scales.       separated  scales,  magnified  350  diameters.  (KoUiker.) 


monly,  in  the  human  subject,  occupies  the  whole  of  the  inside  of  the  hair; 
but  in  some  cases  there  is  left  a  small  central  space  filled  by  a  substance 

called  the  medulla  or  pith,  composed  of  small 
collections  of  irregularly  shaped  cells,  contain- 
ing sometimes  pigment  granules  or  fat,  but 
mostly  air. 

The  follicle,  in  which  the  root  of  each  hair 
is  contained  (Fig.  235),  forms  a  tubular  de- 
pression from  the  surface  of  the  skin, — descend- 
ing into  the  subcutaneous  fat,  generally  to  a 
greater  depth  than  the  sudoriferous  glands,  and 
at  its  deepest  part  enlarging  in  a  bulbous  form, 
and  often  curving  from  its  previous  rectilinear 
course.  It  is  lined  throughout  by  cells  of  epi- 
thelium, continuous  with  those  of  the  epider- 
mis, and  its  walls  are  formed  of  pellucid  mem- 
brane, which  commonly,  in  the  follicles  of  the 
largest  hairs,  has  the  structure  of  vascular 
fibrous  tissue.  At  the  bottom  of  the  follicle  is 
a  small  papilla,  or  projection  of  true  skin,  and 
it  is  by  the  production  and  out-growth  of  epi- 
dermal cells  from  the  surface  of  this  papilla 
that  the  hair  is  formed.  The  inner  wall  of  the 
follicle  is  lined  by  epidermal  cells  continuous 
with  those  covering  the  s^eneral  surface  of  the 
fomdcf'^S"^^^^^^^^  skin;  as  if  indeed  the  follicle  had  been  formed 

^i^^SS'Siea^^^  by  a  simple  thrusting  in  of  tlie  surface  of  the 
2riJt.ri/^<>[;^S;l:;:.%SS;  integument  (Fig.  234).  This  epidermal  lining 
dSmS-'  r\.i!i:X'Z.liVi"inLS  of  the  hair  follicle,  or  root-sheath  of  the  hair, 
X!'nJ"^;5        ^""'"""'-^       is  composed  of  two  layers,  the  inner  one  of 


THE  SKIN  AND  ITS  FUNCTIONS. 


whicli  is  so  moulded  on  the  imbricated  scaly  cuticle  of  the  hair,  that 
its  inner  surface  becomes  imbricated  also,  but  of  course  in  the  opposite 
direction.  When  a  hair  is  pulled  out,  the  inner  layer  of  the  root-sheath 
and  part  of  the  outer  layer  also  are  commonly  pulled  out  with  it. 

Nails. — A  nail,  like  a  hair,  is  a  peculiar  arrangement  of  epidermal 
cells,  the  undermost  of  which,  like  those  of  the  general  surface  of  the 
integument,  are  rounded  or  elongated,  while  the  superficial  are  flattened. 


Fig.  235.  Fig.  236. 

Fig.  235.— Magnified  view  of  the  root  of  a  hair,   ct,  stem  or  shaft  of  hair  cut  across;  6,  inner,  and 

c,  outer  layer  of  the  epidermal  lining  of  the  hair-folUcle,  called  also  the  inner  and  outer  root-sheath; 

d,  dermal  or  external  coat  of  the  hair-follicle,  shown  in  part;  e,  imbricated  scales  about  to  form  a  cor- 
tical layer  on  the  surface  of  the  hair.  The  adjacent  cuticle*  of  the  root-sheath  is  not  represented,  and 
the  papilla  is  hidden  in  the  lower  part  of  the  knob  where  that  is  represented  lighter.  (Kohlraush.) 

Fig.  236.— Transverse  section  of  a  hair  and  hair-follicle  made  below  the  opening  of  the  sebaceous 
gland,  a,  medulla  or  pith  of  the  hair;  6,  fibrous  layer  or  cortex;  c,  cuticle;  d,  Huxley's  layer,  e, 
Henle's  layer  of  internal  root-sheath;  /  and  g,  layers  of  external  root-sheath,  outside  of  (/  is  a  Ught 
layer,  or  glassy  membrane."  which  is  equivalent  to  the  basement  membrane;  /i,  fibrous  coat  of  hair 
sac;  i,  vessels.  (Cadiat.) 


and  of  more  horny  consistence.  That  specially  modified  portion  of  the 
corium,  or  true  skin,  by  which  the  nail  is  secreted,  is  called  the  matrix. 

The  back  edge  of  the  nail,  or  the  root  as  it  is  termed,  is  received  into 
a  shallow  crescentic  groove  in  the  matrix,  while  the  front  part  is  free  and 
projects  beyond  the  extremity  of  the  digit.  The  intermediate  portion  of 
the  nail  rests  by  its  broad  under-surface  on  the  front  part  of  the  matrix, 
which  is  here  called  the  bed  of  the  nail.  This  part  of  the  matrix  is  not 
uniformly  smooth  on  the  surface,  but  is  raised  in  the  form  'of  longitudi- 
nal and  nearly  parallel  ridges  or  laminae,  on  which  are  moulded  the  epi- 
dermal cells  of  which  the  nail  is  made  up  (Fig.  237). 

The  growth  of  the  nail,  like  that  of  the  hair,  or  of  the  epidermis 


342 


HAND-BOOK  OF  PHYSIOLOGY. 


generally,  is  effected  by  a  constant  production  of  cells  from  beneath  and 
behind,  to  take  the  place  of  those  which  are  worn  or  cut  away.  Inas- 
much, however,  as  the  posterior  edge  of  the  nail,  from  its  being  lodged  in 
a  groove  of  the  skin,  cannot  grow  backward,  on  additions  being  made  to 
it,  so  easily  as  it  can  pass  in  the  opposite  direction,  any  growth  at  its 
hinder  part  pushes  the  whole  forward.  At  the  same  time  fresh  cells  are 
added  to  its  under  surface,  and  thus  each  portion  of  the  nail  becomes 
gradually  thicker  as  it  moves  to  the  front,  until,  projecting  beyond  the 


a. 


Fig.  237,— Vertical  transverse  section  through  a  small  portion  of  the  nail  and  matrix  largely- 
magnified.  J.,  corium  of  the  nail-bed,  raised  into  ridges  or  laminae  a,  fitting  in  between  correspond- 
ing laminae  6,  of  the  nail,  i?,  IMalpighiau,  and  C,  horny  layer  of  nail ;  d,  deepest  and  vertical  cells ;  e, 
upper  flattened  ceUs  of  Malpighian  layer.  ^,K611iker.) 

surface  of  the  matrix,  it  can  receive  no  fresh  addition  from  beneath,  and 
is  simply  moved  forward  by  the  growth  at  its  root,  to  be  at  last  worn 
away  or  cut  off. 

Fu^^'CTIONS  OF  THE  SkIN". 

(1.)  By  means  of  its  toughness,  flexibility  and  elasticity,  the  skin  is 
eminently  qualified  to  serve  as  the  general  integument  of  the  body,  for 
defending  the  internal  parts  from  external  violence,  and  readily  yielding 
and  adapting  itself  to  their  various  movements  and  changes  of  position. 

(2.)  The  skin  is  the  cliief  organ  of  the  sense  of  touch.  Its  whole  sur- 
face is  extremely  sensitive;  but  its  tactile  properties  are  due  more  espe- 
cially to  the  abundant  papillae  with  which  it  is  studded.  (See  Chapter 
on  Special  Senses.) 

Although  destined  especially  for  the  sense  of  touch,  the  papillae  are 
not  so  placed  as  to  come  into  direct  contact  with  external  objects;  but 


THE  SKIN  AND  ITS  FUNCTIONS. 


343 


like  the  rest  of  the  surface  of  the  skin,  are  covered  by  one  or  more  layers 
of  epithelium^  forming  the  cuticle  or  epidermis.  The  jmpillse  adhere 
very  intimately  to  the  cuticle,  which  is  thickest  in  the  spaces  between 
them, -but  tolerably  level  on  its  outer  surface:  hence,  when  stripped  otf 
from  the  cutis,  as  after  maceration,  its  internal  surface  presents  a  series 
of  pits  and  elevations  corresponding  to  the  papillae  and  their  interspaces, 
of  which  it  thus  forms  a  kind  of  mould.  Besides  affording  by  its  imper- 
meability a  check  to  undue  evaporation  from  the  skin,  and  providing  the 
sensitive  cutis  with  a  protecting  investment,  the  cuticle  is  of  service  in 
relation  to  the  sense  of  touch.  For  by  being  thickest  in  the  spaces,  be- 
tween the  papillae,  and  only  thinly  spread  over  the  summits  of  these  pro- 
cesses, it  may  serve  to  subdivide  the  sentient  surface  of  the  skin  into  a 
number  of  isolated  points,  each  of  which  is  capable  of  receiving  a  distinct 
impression  from  an  external  body.  By  covering  the  papillae  it  renders 
the  sensation  produced  by  external  bodies  more  obtuse,  and  in  this  manner 
also  is  subservient  to  touch:  for  unless  the  very  sensitive  papillae  were 
thus  defended,  the  contact  of  substances  would  give  rise  to  pain,  instead 
of  the  ordinary  impressions  of  touch.  This  is  shown  in  the  extreme  sensi- 
tiveness and  loss  of  tactile  power  in  a  part  of  the  skin  when  deprived  of 
its  epidermis.  If  the  cuticle  is  very  thick,  however,  as  on  the  heel,  touch 
becomes  imperfect,  or  is  lost. 

(3.)  The  Secretion  of  Sebaceous  Glands,  and  Hair-follicles. — 
The  secretion  of  the  sebaceous  glands  and  hair -follicles  (for  their  products 
cannot  be  separated)  consists  of  cast-off  epithelium-cells,  with  nuclei  and 
granules,  together  with  an  oily  matter,  extractive  matter,  and  stearin; 
in  certain  parts,  also,  it  is  mixed  with  a  peculiar  odorous  principle,  which 
contains  caproic,  butyric,  and  rutic  acids.  It  is,  perhaps,  nearly  similar 
in  composition  to  the  unctuous  coating,  or  vernix  caseosa,  which  is  formed 
on  the  body  of  the  foetus  while  in  the  uterus,  and  which  contains  large 
quantities  of  ordinary  fat.  Its  purpose  seems  to  be  that  of  keeping  the  skin 
moist  and  supple,  and,  by  its  oily  nature,  of  both  hindering  the  evapora- 
tion from  the  surface,  and  guarding  the  skin  from  the  effects  of  the  long- 
continued  action  of  moisture.  But  while  it  thus  serves  local  purposes,  its 
removal  from  the  body  entitles  it  to  be  reckoned  among  the  excretions  of 
the  skin;  though  the  share  it  has  in  the  purifying  of  the  blood  cannot  be 
discerned. 

(4.)  The  Excretion  of  the  Skin:  the  Sweat. — The  fluid  secreted 
by  the  sudoriferous  glands  is  usually  formed  so  gradually,  that  the  watery 
portion  of  it  escapes  by  evaporation  as  fast  as  it  reaches  the  surface.  But, 
during  strong  exercise,  exposure  to  great  external  warmth,  in  some  dis- 
eases, and  when  evaporation  is  prevented,  the  secretion  becomes  more 
sensible,  and  collects  on  the  skin  in  the  form  of  drops  of  fluid. 

The  perspiration  of  the  skin,  as  the  term  is  sometimes  employed  in 
physiology,  includes  all  that  portion  of  the  secretions  and  exudations  from 


344 


HAND-BOOK  OF  PHYSIOLOGY. 


the  skin  which  passes  off  by  evaporation;  the  sweat  includes  that  which 
may  be  collected  only  in  drops  of  fluid  on  the  surface  of  the  skin.  The 
two  terms  are,  however,  most  often  used  synonymously;  and  for  distinc- 
tion, the  former  is  called  insensiUe  perspiration;  the  latter  sensiMe  per- 
spiration. The  fluids  are  the  same,  except  that  the  sweat  is  commonly 
mingled  with  various  substances  lying  on  the  surface  of  the  skin.  The 
contents  of  the  sweat  are,  in  part,  matters  capable  of  assuming  the  form 
of  vapor,  such  as  carbonic  acid  and  water,  and  in  part,  other  matters 
which  are  deposited  on  the  skin,  and  mixed  with  the  sebaceous  secretion. 


Table  of  the  Chemical  Composition  of  Sweat. 

Water  995 

Solids:— 

Organic  Acids  (formic,  acetic,  butyric,  pro- )  ,q 

picnic,  caproic,  caprylic)   .       .       .  j 
Salts,  chiefly  sodium  chloride       .       .  .1*8 
Neutral  fats  and  cholesterin  .       .       .       .  '7 
Extractives  (including  urea),  with  epithelium  1  -6  5 


1000 


Of  these  several  substances,  however,  only  the  carbonic  acid  and  water 
need  particular  consideration. 

Watery  Vapor. — The  quantity  of  watery  vapor  excreted  from  the 
skin  is  on  an  average  between  and  2  lb.  daily.  This  subject  has  been 
estimated  very  carefully  by  Lavoisier  and  Sequin.  The  latter  chemist 
enclosed  his  body  in  an  air-tight  bag,  with  a  mouth-piece.  The  bag 
being  closed  by  a  strong  band  above,  and  the  mouth-piece  adjusted  and 
gummed  to  the  skin  around  the  mouth,  he  was  weighed,  and  then  re- 
mained quiet  for  several  hours,  after  which  time  he  was  again  weighed. 
The  difference  in  the  two  weights  indicated  the  amount  of  loss  by  pul- 
monary exhalation.  Having  taken  off  the  air-tight  dress,  he  was  imme- 
diately weighed  again,  and  a  fourth  time  after  a  certain  interval.  The 
difference  between  the  Wo  weights  last  ascertained  gave  the  amount  of 
the  cutaneous  and  pulmonary  exhalation  together;  by  subtracting  from 
this  the  loss  by  pulmonary  exhalation  alone,  while  he  was  in  the  air-tight 
dress,  he  ascertained  the  amount  of  cutaneous  transpiration.  During  a 
state  of  rest,  the  average  loss  by  cutaneous  and  pulmonary  exhalation  in 
a  minute,  is  eighteen  grains, — tlie  minimum  eleven  grains,  the  maximum 
thirty-two  grains;  and  of  the  eighteen  grains,  eleven  pass  off  by  the  skin, 
and  seven  by  the  lungs. 

The  quantity  of  watery  vapor  lost  by  transpiration  is  of  course  influ- 
enced by  all  external  circumstances  which  affect  the  exhalation  from 
other  evaporating  surfaces,  such  as  the  temjierature,  the  liygrometric 


THE  SKIN  AND  ITS  FUNCTIONS. 


1-5 


state,  and  the  stillness  of  the  atmosphere.  But,  of  the  variations  to 
which  it  is  subject  under  the  influence  of  these  conditions,  no  calculation 
has  been  exactly  made. 

Carbonic  Acid. — The  quantity  of  carbonic  acid  exhaled  by  the  skin 
on  an  average  is  about  y^-  to  of  that  furnished  by  the  pulmonary 
respiration. 

The  cutaneous  exhalation  is  most  abundant  in  the  lower  classes  of 
animals,  more  particularly  the  naked  Amphibia,  as  frogs  and  toads,  whose 
skin  is  thin  and  moist,  and  readily  permits  an  interchange  of  gases  be- 
tween the  blood  circulating  in  it  and  the  surrounding  atmosphere. 
Bischoff  found  that,  after  the  lungs  of  frogs  had  been  tied  and  cut  out, 
about  a  quarter  of  a  cubic  inch  of  carbonic  acid  gas  was  exhaled  by  the 
skin  in  eight  hours.  And  this  quantity  is  very  large,  when  it  is  remem- 
bered that  a  full-sized  frog  will  generate  only  about  half  a  cubic  inch  of 
carbonic  acid  by  his  lungs  and  skin  together  in  six  hours.  (Milne- 
Edwards  and  Miiller.) 

The  importance  of  the  respiratory  function  of  the  skin,  which  was 
once  thought  to  be  proved  by  the  speedy  death  of  animals  whose  skins, 
after  removal  of  the  hair,  were  covered  wdth  an  impermeable  varnish,  has 
been  shown  by  further  observations  to  have  no  foundation  in  fact;  the 
immediate  cause  of  death  in  such  cases  being  the  loss  of  temperature.  A 
varnished  animal  is  said  to  have  suffered  no  harm  when  surrounded  by 
cotton  wadding,  and  to  have  died  when  the  wadding  was  removed. 

Influence  of  the  Nervous  System  on  Excretion. — Any  increase 
in  the  amount  of  sweat  secreted  is  usually  accompanied  by  dilatation  of 
the  cutaneous  vessels.  It  is,  however,  probable  that  the  secretion  is  like 
the  other  secretions,  e.g.,  the  saliva,  under  the  direct  action  of  a  special 
nervous  apparatus,  in  that  various  nerves  contain  fibres  which  act  directly 
upon  the  cells  of  the  sweat  glands  in  the  same  way  that  the  chorda  tym- 
pani  contains  fibres  which  act  directly  upon  the  salivary  cells.  The  nerve 
fibres  which  induce  sweating  may  act  independently  of  the  vaso-motor 
fibres,  whether  vaso-dilator  or  vaso-constrictor.  The  local  apparatus  is 
■under  control  of  the  central  nervous  system — sweat  centres  probably  ex- 
isting both  in  the  medulla  and  spinal  cord — and  may  be  reflexly  as  well  a& 
directly  excited.  This  will  explain  the  fact  that  sweat  occurs  not  only 
when  the  skin  is  red,  but  also  when  it  is  pale,  and  the  cutaneous  circula- 
tion languid,  as  in  the  sweat  which  accompanies  syncope  or  fainting,  or 
which  immediately  precedes  death. 

(5.)  Absorption  by  the  Skin. — Absorption  by  the  skin  has  been 
already  mentioned,  as  an  instance  in  which  that  process  is  most  actively 
accomplished.  Metallic  preparations  rubbed  into  the  skin  have  the  same 
action  as  when  given  internally,  only  in  a  less  degree.  Mercury  applied 
in  this  manner  exerts  its  specific  influence  upon  syphilis,  and  excites  sali- 
vation; potassio-tartrate  of  antimony  may  excite  vomiting,  or  an  eruption 
extending  over  the  whole  body;   and  arsenic  may  produce  poisonous 


346 


HAND-BOOK  OF  PHYSIOLOGY. 


effects.  Vegetable  matters,  also,  if  soluble,  or  already  in  solution,  give 
rise  to  their  peculiar  effects,  as  cathartics,  narcotics,  and  the  like,  when 
rubbed  into  the  skin.  The  effect  of  rubbing  is  probably  to  convey  the 
particles  of  the  matter  into  the  orifices  of  the  glands,  whence  they  are 
more  readily  absorbed  than  they  would  be  through  the  epidermis.  When 
simply  left  in  contact  with  the  skin,  substances,  unless  in  a  fluid  state, 
are  seldom  absorbed. 

It  has  long  been  a  contested  question  whether  the  skin  covered  with 
the  epidermis  has  the  power  of  absorbing  water;  and  it  is  a  point  the 
more  difficult  to  determine  because  the  skin  loses  water  by  evaporation. 
But,  from  the  result  of  many  experiments,  it  may  now  be  regarded  as  a 
well-ascertained  fact  that  such  absorption  really  occurs.  The  absorption 
of  water  by  the  surface  of  the  body  may  take  place  in  the  lower  animals 
very  rapidly.  Not  only  frogs,  which  have  a  thin  skin,  but  lizards,  in 
which  the  cuticle  is  thicker  than  in  man,  after  having  lost  weight  by 
being  kept  for  some  time  in  a  dry  atmosphere,  were  found  to  recover  both 
their  weight  and  plumpness  very  rapidly  when  immersed  in  water.  When 
merely  the  tail,  posterior  extremities,  and  posterior  part  of  the  body  of 
the  lizard  were  immersed,  the  water  absorbed  was  distributed  throughout 
the  system.  And  a  like  absorption  through  the  skin,  though  to  a  less 
extent,  may  take  place  also  in  man. 

In  severe  cases  of  dysphagia,  when  not  even  fluids  can  be  taken  into 
the  stomach,  immersion  in  a  bath  of  warm  water  or  of  milk  and  water 
may  assuage  the  thirst;  and  it  has  been  found  in  such  cases  that  the 
weight  of  the  body  is  increased  by  the  immersion.  Sailors  also,  when 
destitute  of  fresh  water,  find  their  urgent  thirst  allayed  by  soaking  their 
clothes  in  salt  water  and  wearing  them  in  that  state;  but  these  effects  are 
in  part  due  to  the  hindrance  to  the  evaporation  of  water  from  the  skin. 

(6.)  Regulation  of  Temperature. — For  an  account  of  this  impor- 
tant function  of  the  skin,  see  Chapter  on  Animal  Heat. 


CHAPTER  XIII. 


THE  KIDNEYS  AND  THE  EXCRETION  OF  URINE. 

The  Kidneys  are  two  in  number,  and  are  situated  deeply  in  the  lum- 
bar region  of  the  abdomen,  on  either  side  of  the  spinal  column,  behind 
the  peritoneum.  They  correspond  in  position  to  the  last  two  dorsal  and 
two  upper  lumbar  vertebrae;  the  right  being  slightly  lower  than  the  left 
in  consequence  of  the  position  of  the  liver  on  the  right  side  of  the  abdo- 
men. They  are  characteristic  in  shape,  about  4  inches  long,  2^  inches 
broad,  and  1^  inch  thick.    The  weight  of  each  kidney  is  about  4|-  oz. 


Fig.  238.— Plan  of  a  longitudinal  section  through  the  pelvis  and  substance  of  the  right  kidney, 
a,  the  cortical  substance;  6,  6,  broad  part  of  the  pyramids  of  Malpighii;  c,  c,  the  divisions  of  the  pel- 
vis named  calyces,  laid  open;  c',  one  of  those  unopened;  d,  summit  of  the  pyramids  of  papillas  pro- 
jecting into  calyces;  e,  e,  section  of  the  narrow  part  of  two  pyramids  near  the  calyces:  p,  pelvis  or 
enlarged  divisions  of  the  ureter  within  the  kidney;  u.  the  ureter;  s,  the  sinus;  /i,  the  hilus. 

Structure  of  the  Kidneys. — The  kidney  is  covered  by  a  rather 
tough  fibrous  capsule,  which  is  slightly  attached  by  its  inner  surface  to 
the  proper  substance  of  the  organ  by  means  of  very  fine  fibres  of  areolar 
tissue  and  minute  blood-vessels.  From  the  healthy  kidney,  therefore,  it 
may  be  easily  torn  off  without  injury  to  the  subjacent  cortical  portion  of 
the  organ.  At  the  hilus  or  notch  of  the  kidney,  it  becomes  continuous 
with  the  external  coat  of  the  upper  and  dilated  part  of  the  ureter  (Fig. 
238). 


348 


HAND-BOOK  OF  PHYSIOLOGY. 


On  making  a  section  lengthwise  through  the  kidney  (Fig.  238)  the 
main  part  of  its  substance  is  seen  to  be  composed  of  two  chief  portions, 
called  respectively  the  cortical  and  the  medullary  portion,  the  latter  being 
also  sometimes  called  the  ])yramidal  portion,  from  the  fact  of  its  being 
composed  of  about  a  dozen  conical  bundles  of  urine-tube,  each  bundle 
being  called  a  pyramid.  The  upper  part  of  the  duct  of  the  organ,  or  the 
ureter,  is  dilated  into  what  is  called  the  j^elvis  of  the  kidney;  and  this, 
again,  after  separating  into  two  or  three  principal  divisions,  is  finally  sub- 
divided into  still  smaller  portions,  varying  in  number  from  about  8  to  12, 
or  even  more,  and  called  calyces.  Each  of  these  little  calyces  or  cups, 
which  are  often  arranged  in  a  double  row,  receives  the  pointed  extremity 
papilla  of  sl  pyramid.  Sometimes,  however,  more  than  one  j^apilla  is 
received  by  a  calyx. 

The  kidney  is  a  compound  tuhilar  gland,  and  both  its  cortical  and 
medullary  portions  are  composed  essentially  of  secreting  tubes,  the  tuhuli 
urinifer  i,  which,  by  one  extremity,  in  the  corticcd  portion,  end  commonly 
in  little  saccules  containing  blood-vessels,  called  Malpigliian  dodies,  and, 
by  the  other,  open  through  the  papillce  into  the  pelvis  of  the  kidney,  and 
thus  discharge  the  urine  which  flows  through  them. 


A. 


Fig.  239.— a.  Portion  of  a  secreting  tubule  from  the  cortical  substance  of  the  kidney,  b.  The  epi- 
thelial or  gland-cells.    X  700  times. 

In  the  pyramids  the  tubes  are  chiefly  straight — dividing  and  diverg- 
ing as  they  ascend  through  these  into  the  cortical  portion;  while  in  the 
latter  region  they  spread  out  more  irregularly,  and  become  much  branched 
and  convoluted. 

Tubuli  Uriniferi. — The  tubuli  uriniferi  (Fig.  239)  are  composed  of 
a  nearly  homogeneous  membrane,  and  are  lined  internally  by  epithelium. 
They  vary  considerably  in  size  in  different  parts  (^f  their  course,  but  are, 
on  an  average,  about  ^  J  j  of  an  inch  in  diameter,  and  are  found  to  be 


THE  KIDNEYS  AND  URINE.  349 

made  up  of  several  distinct  sections  which  differ  from  one  another  very 
markedly,  both  in  situation  and  structure.  According  to  Klein,  the  fol- 
lowing segments  may  be  made  out:  (1)  The  MalpigUan  corpuscle  (Figs. 


■  1 


Fig.  240.—  A  Diagram  of  the  sections  of  viriniferous  tubes.  A,  Cortex  limited  externally  by  the 
<;apsule;  a,  subcapsular  layer  not  containing  Malpighian  corpuscles;  a',  inner  stratum  of  cortex,  also 
without  Malpighian  capsules;  B,  Boundary  layer;  C,  Papillary  part  next  the  boundary  layer;  1,  Bow- 
man's capsule  of  Malpighian  corpuscle;  2,  neck  of  capsule;  3.  proximal  convoluted  tubule;  4,  spiral 
tubule  of  Schachowa:  5,  descending  limb  of  Henle's  loop;  6,  the  loop  proper;  7,  thick  part  of  the  as- 
cending hmb;  8,  spiral  part  of  ascending  limb;  9,  narrow  ascending  limb  in  the  medullary  ray;  10, 
the  irregular  tubule;  11,  the  intercalated  section  of  Schweigger-Seidel,  or  the  distal  convoluted  tubule; 
12,  the  curved  collecting  tubule;  13,  the  straight  collecting  tubule  of  the  medullary  ray;  14,  the  col- 
lecting tube  of  the  boundary  layer;  15,  the  large  collecting  tube  of  the  papillary  part  which,  joining 
with  similar  tubes,  forms  the  duct,   (Klein  and  Noble  Smith.) 


240,  241),  composed  of  a  hyaline  membrana  propria,  thickened  by  a  vary- 
ing amount  of  fibrous  tissue,  and  lined  by  flattened  nucleated  epithelial 


350 


HAND-BOOK  OF  PHYSIOLOGY. 


plates.  This  capsule  is  the  dilated  extremity  of  the  uriniferous  tubule, 
and  contains  within  it  a  glomerulus  of  convoluted  capillary  blood-vessels 
supported  by  connective  tissue,  and  covered  by  flattened  epithelial  plates. 
The  glomerulus  is  connected  with  an  efferent  and  an  afferent  vessel.  (2) 
The  constricted  neck  of  the  capsule  (Fig.  240,  2),  lined  in  a  similar  man- 
ner, connects  it  with  (3)  The  Proximal  convoluted  tubule,  which  forms 
several  distinct  curves  and  is  lined  with  short  columnar  cells,  which  vary 
somewhat  in  size.  The  tube  next  passes  almost  vertically  down-a^ard, 
forming  (4)  The  8j)iral  tubule,  which  is  of  much  the         diameter  «-nd 


Fig.  241.— From  a  vertical  section  through  the  kidney  of  a  dog— the  capsule  of  which  is  suppose(J 
to  be  on  the  right,  a.  The  capillaries  of  the  Malpighian  corpuscle— A-iz.,  the  glomerulus,  are  arrangecl 
in  lobules;  n,  neck  of  capsule;  c,  convoluted  tubes  cut  in  various  directions;  ft,  irregular  tubule;  d,  e, 
and  /,  are  straight  tubes  running  toward  capsules  forming  a  so-called  niedullary  ray;  d,  collecting 
tube;  e,  spiral  tube;  /,  narrow  section  of  ascending  limb.    X  380.   (Klein  and  Noble  Smith.) 

is  lined  in  the  same  way  as  the  convoluted  portion.  So  far  the  tube  has 
been  contained  in  the  cortex  of  the  kidney,  it  now  passes  vertically  down- 
ward through  the  most  external  part  (boundary  layer)  of  the  Malpighian 
pyramid  into  the  more  internal  part  (papillary  layer),  where  it  curves  up 
sharply,  forming  altogether  the  ( 5  and  G)  Loop  of  Henle,  which  is  a  very 
narrow  tube  lined  with  flattened  nucleated  cells.  Passing  vertically  up- 
ward just  as  the  tube  reaches  the  boundary  layer  (7)  it  suddenly  enlarges 
and  becomes  lined  Avith  })olylicdral  cells.  (8)  About  midway  in  the  boun- 
dary layer  the  tube  again  narrows,  forming  the  ascending  spiral  of 
Henle's  loop,  but  is  still  lined  with  polyhedral  cells.  At  the  point  where 
the  tube  enters  the  cortex  (!))  the  ascending  limb  narrows,  but  the  diame- 


THE  KIDNEYS  AND  UEINE. 


351 


ter  varies  considerably;  here  and  there  the  cells  are  more  flattened,  but 
both  in  this  as  in  (8)  the  cells  are  in  many  places  very  angular,  branched, 
and  imbricated.  It  then  joins  (10)  the  ^Hrregidar  tubule"  which  has  a 
very  irregular  and  angular  outline,  and  is  lined  with  angular  and  imbri- 
cated cells.  The  tube  next  becomes  convoluted,  (11)  forming  the  didal 
convoluted  tube  or  intercalated  section  of  8cliweigger-Seidel,  which  is 
identical  in  all  respects  with  the  proximal  convoluted  tube  (12  and  13). 
The  curved  and  straight  collecting  tubes,  the  former  entering  the  latter 
at  right  angles,  and  the  latter  passing  vertically  downward,  are  lined  with 
polyhedral,  or  spindle-shaped,  or  flattened,  or  angular  cells.  The  straight 
collecting  tube  now  enters  the  boundary  layer  (14),  and  passes  on  to  the 


Fig.  242.— Transverse  section  of  a  renal  papilla;  a,  larger  tubes  or  papillary  ducts;  &,  smaller 
tubes  of  Henle;  c,  blood-vessels,  distinguished  by  their  flatter  epithelium;  d,  nuclei  of  the  stroma. 
(Kolhker.)    x  300. 

Fig.  243.— Diagram  showing  the  relation  of  the  Malpighian  body  to  the  uriniferous  ducts  and 
blood-vessels,  a,  one  of  the  interlobular  arteries;  a',  afferent  artery  passing  into  the  glomerulus;  c, 
capsule  of  the  Malpighian  body,  forming  the  termination  of  and  continuous  with  the  uriniferous 
tube;  e',  e',  efferent  vessels  which  subdivide  in  the  plexus  p,  surrounding  the  tube,  and  finally  ter- 
minate in  the  branch  of  the  renal  vein  e  (after  Bowman). 


papillary  layer,  and,  joining  with  other  collecting  tuoes,  form  larger 
tubes,  which  finally  open  at  the  apex  of  the  papilla.  These  collecting 
tubes  are  lined  with  transparent  nucleated  columnar  or  cubical  cells  (14, 


The  cells  of  the  tubules  with  the  exception  of  Henle^s  loop  and  all 
parts  of  the  collecting  tubules,  are,  as  a  rule,  possessed  of  the  intra-nuclear 
as  well  as  of  the  intra- cellular  network  of  fibres,  of  which  the  vertical  rods 
are  most  conspicuous  parts. 

Heidenhain  observed  that  indigo-sulphate  of  sodium,  and  other  pig- 
ments injected  into  the  jugular  vein  of  an  animal,  were  apparently  ex- 
creted by  the  cells  which  possessed  these  rods,  and  therefore  concluded 
that  the  pigment  passes  through  the  cells,  rods,  and  nucleus  themselves. 


Fig.  242. 


Fig.  243. 


15,  16). 


352 


HAND-BOOK  OF  PHYSIOLOGY. 


Klein,  however,  believes  that  the  pigment  passes  through  the  intercellular 
substances,  and  not  through  the  cells. 

In  some  places,  it  is  stated  that  a  distinct  membrane  of  flattened  cells 
can  be  made  out  lining  the  lumen  of  the  tubes  {centrotuhular  membrane). 

Blood-vessels  of  Kidneys. — In  connection  with  the  general  distri- 
bution of  blood-vessels  to  the  kidney,  the  MalpigMan  Corpuscles  may  be 
further  considered.  They  (Fig.  243)  are  found  only  in  the  cortical  part 
of  the  kidney,  and  are  confined  to  the  central  part,  which,  however, 
makes  up  about  seven-eighths  of  the  whole  cortex.  On  a  section  of  the 
organ,  some  of  them  are  just  visible  to  the  naked  eye  as  minute  red  points; 
others  are  too  small  to  be  thus  seen.  Their  average  diameter  is  about 
yl-g-  of  an  inch.  Each  of  them  is  composed,  as  we  have  seen  above,  of 
the  dilated  extremity  of  a  urinary  tube,  or  Malpighian  capsule,  enclosing 
a  tuft  of  blood-vessels. 

The  renal  artery  divides  into  several  branches,  which,  passing  in  at 
the  hilus  of  the  kidney,  and  covered  by  a  fine  sheath  of  areolar  tissue 
derived  from  the  capsule,  enter  the  substance  of  the  organ  in  the  inter- 
vals between  the  papillae,  chiefly  at  the  junction  between  the  cortex  and 
the  boundary  layer.  The  chief  branches  then  pass  almost  horizontally, 
giving  off  smaller  branches  upward  to  the  cortex  and  downward  to  the 
medulla.  The  former  are  for  the  most  part  straight,  they  pass  almost 
vertically  to  the  surface  of  the  kidney,  giving  off  laterally  in  all  directions 
longer  or  shorter  branches,  which  supply  the  afferent  arteries  to  the  Mal- 
pighian bodies. 

The  small  afferent  artery  (Figs.  243  and  245)  which  enters  the  Mal- 
pighian corpuscle,  breaks  up  as  before  mentioned  in  the  interior  into  a 
dense  and  convoluted  and  looped  capillary  plexus,  which  is  ultimately 
gathered  up  again  into  a  single  small  efferent  vessel,  comparable  to  a  min- 
ute vein,  which  leaves  the  Malpighian  capsule  just  by  the  point  at  which 
the  afferent  artery  enters  it.  On  leaving,  it  does  not  immediately  join 
other  small  veins  as  might  have  been  expected,  but  again  breaking  up  into 
a  network  of  capillary  vessels,  is  distributed  on  the  exterior  of  the  tubule, 
from  whose  dilated  end  it  had  just  emerged.  After  this  second  breaking 
up  it  is  finally  collected  into  a  small  vein,  which,  by  union  with  others 
like  it,  helps  to  form  the  radicles  of  the  renal  vein.  Thus,  in  the  kidney, 
the  blood  entering  by  the  renal  artery  traverses  tivo  sets  of  capillaries  be- 
fore emerging  by  the  renal  vein,  an  arrangement  which  may  be  compared 
to  the  portal  system  in  miniature. 

The  tuft  of  vessels  in  the  course  of  development  is,  as  .  were,  thrust 
into  the  dilated  extremity  of  the  urinary  tubule,  which  finally  completely 
invests  it  just  as  the  pleura  invests  the  lungs  or  the  tunica  vaginalis  the 
testicle.  Thus  tlic  Malpighian  capsule  is  lined  by  a  parietal  layer  of 
squ.'imous  cells  and  a  visceral  or  reflected  layer  immediately  covering  the 
vascular  tuft  (Fig.  241 ),  and  sometimes  dipping  down  into  its  interstices. 


THE  KIDNEYS  AND  URINE. 


353 


This  reflected  layer  of  epithelium  is  readily  seen  in  young  subjects,  but 
cannot  always  be  demonstrated  in  the  adult.    (See  Figs.  244  and  245.) 

The  vessels  which  enter  the  medullary  layer  break  up  into  smaller 
arterioles,  which  pass  through  the  boundary  layer  and  proceed  in  a 
straight  course  between  the  tubules  of  the  papillary  layer,  giving  off  on 
their  way  branches,  which  form  a  fine  arterial  meshwork  around  the  tubes, 
and  end  in  a  similar  plexus,  from  which  the  venous  radicles  arise. 

Besides  the  small  afferent  arteries  of  the  Malpighian  bodies,  there  are, 
of  course,  others  which  are  distributed  in  the  ordinary  manner,  for  nutri- 
tion's sake,  to  the  different  parts  of  the  organ;  and  in  the  pyramids,  be- 


FiG.  244.— Transverse  section  of  a  devdoping  Malpighian  capsule  and  tuft  (human)  x  300.  From 
a  foetus  at  about  the  fourth  month;  a,  iSattened  cells  growing  to  form  the  capsule;  6,  more  roimded 
cells,  continuous  with  the  above,  reflected  round  c,  and  finally  enveloping  it;  c,  mass  of  embryonic 
ceUs  w^hich  will  later  become  developed  into  blood-vessels.   (W.  Pye.) 

Fig.  245.— Epithelial  elements  of  a  Malpighian  capsule  and  tuft,  with  the  commencement  of  a 
urinary  tubule  showing  the  afferent  and  efferent  vessel ;  a,  layer  of  tessellated  epithelium  forming  the 
capsule;  6,  similar,  but  rather  larger  epithelial  cells,  placed  in  the  waUs  of  the  tube;  c,  cells,  covering 
the  vessels  of  the  capillary  tuft;  d,  commencement  of  the  tubule,  somewhat- narrower  than  the  rest 
of  it.    (W^  Pye.) 


tween  the  tubes,  there  are  numerous  straight  vessels,  the  vasta  recta,  sup- 
posed by  some  observers  to  be  branches  of  vasa  efferentia  from  Malpighian 
bodies,  and  therefore  comparable  to  the  venous  plexus  around  the  tubules 
in  the  cortical  portion,  while  others  think  that  they  arise  directly  from 
small  branches  of  the  renal  arteries. 

Between  the  tubes,  vessels,  etc.,  which  make  up  the  substance  of  the 
kidney,  there  exists,  in  small  quantity,  a  fine  matrix  of  areolar  tissue. 
Nerves. — The  nerves  of  the  kidney  are  derived  from  the  renal  plexus^ 
Structure  of  the  Ureters. — The  duct  of  the  kidney,  or  ureter,  is  a, 
tube  about  the  size  of  a  goose-quill,  and  from  a  foot  to  sixteen  inches  in 
length,  which,  continuous  above  with  the  pelvis  of  the  kidney,  ends 
below  by  perforating  obliquely  the  walls  of  the  bladder,  and  opening  on 
YoL.  I.— 23. 


Fig.  244. 


Fig.  245. 


354  HAOT-BOOK  OF  PHYSIOLOGY. 

its  internal  surface.  It  is  constructed  of  three  principal  coats  (a)  an 
outer,  tough,  fibrous  and  elastic  coat;  {h)  a  middle,  muscular  coat,  of 
wliicli  the  fibres  are  unstriped,  and  arranged  in  three  layers — the  fibres 
of  the  central  layer  beijig  circular,  and  those  of  the  other  two  longitudinal 
in  direction;  and  (r)  an  internal  mucous  lining  continuous  with  that  of 
the  pelvis  of  the  kidney  above,  and  of  the  urinary  bladder  below.  The 
epithelium  of  all  these  parts  (Fig.  ;3-46)  is  alike  stratified  and  of  a  some- 
what peculiar  form;  the  cells  on  the  free  surface  of  the  mucous  mem- 
brane being  usually  spheroidal  or  polyhedral  with  one  or  more  spherical  or 
oval  nuclei;  while  beneath  these  are  pear-shaped  cells,  of  which  the  broad 
ends  are  directed  toward  the  free  surface,  fitting  in  beneath  the  cells  of 
the  first  row,  and  the  apices  are  prolonged  into  processes  of  various 
lengths,  among  which,  again,  the  deepest  cells  of  the  epithelium  are 
found  spheroidal,  irregularly  oval,  spindle-shaped  or  conical. 

Structure  of  Urinary  Bladder. — The  urinary  bladder,  which 
forms  a  receptacle  for  the  temporary  lodgment  of  the  urine  in  the  intervals 
of  its  expulsion  from  the  body,  is  more  or  less  pyrif orm,  its  widest  part, 
which  is  situate  above  and  behind,  being  termed  the  fundus:  and  the 
narrow  constricted  portion  in  front  and  below,  by  which  it  becomes  con- 
tinuous with  the  urethra,  being  called  its  cervix  or  nech.  It  is  constructed 
of  four  principal  coats, — serous,  muscular,  areolar  or  submucous,  and 
miicous.  {a)  The  serous  coat,  which  covers  only  the  posterior  and  upper 
half  of  the  bladder,  has  tlie  same  structure  as  that  of  the  peritoneum. 


Fig.  246.— Epithelium  of  the  bladder;  a,  one  of  the  ceUs  of  the  first  row;  6,  a  cell  of  the  second 
row;  c,  cells  in  situ,  of  first,  second,  and  deepest  layers.  (Oberstemer.) 

with  which  it  is  continuous,  {b)  The  fibres  of  the  muscular  coat,  which 
are  unstriped,  are  arranged  in  three  principal  layers,  of  which  the  external 
and  internal  (Ellis)  have  a  general  longitudinal,  and  the  middle  layer  a 
circular  direction.  The  latter  are  especially  developed  around  the  cervix 
of  the  organ,  and  are  described  as  forming  a  spJiincter  vesica'.  The  mus- 
cular fibres  of  the  bladder,  like  those  of  the  stomach,  are  arranged  not  in 
simple  circles,  but  in  figure-of-8  loops,  (c)  The  areolar  or  submucous 
coat  is  constructed  of  connective  tissue  with  a  large  proportion  of  elastic 
fibres,  (d)  The  mucous  membrane,  which  is  rugose  in  the  contracted 
state  of  the  organ,  does  not  dilTer  in  essential  structure  from  mucous 


THE  KIDNEYS  AND  URINE. 


355 


membranes  in  general.  Its  epithelium  is  stratified  and  closely  resembles 
that  of  the  pelvis  of  the  kidney  and  the  ureter  (Fig.  246). 

The  mucous  membrane  is  provided  with  mucous  glands,  which  are 
more  numerous  near  the  neck  of  the  bladder. 

The  bladder  is  well  provided  with  blood  and  lymph  vessels,  and  with 
nerves.  The  latter  are  branches  from  the  sacral  plexus  (spinal)  and  hypo- 
gastric plexus  (sympathetic).  A  few  ganglion-cells  are  found,  here  and 
there,  in  the  course  of  the  nerve -fibres. 


The  Exceetion  of  the  Kidney  : — The  Ukine. 

Physical  Properties. — Healthy  urine  is  a  perfectly  transparent, 
amber-colored  liquid,  with  a  peculiar,  but  not  disagreeable  odor,  a  bitter- 
ish taste,  and  slight  acid  reaction.  Its  specific  gravity  varies  from  1015 
to  1025.  On  standing  for  a  short  time,  a  little  mucous  appears  in  it  as 
a  flocculent  cloud. 

Chemical  Composition. — The  urine  consists  of  water,  holding  in 
solution  certain  organic  and  saline  matters  as  its  ordinary  constituents, 
and  occasionally  various  matters  taken  into  the  stomach  as  food — salts, 
coloring  matter,  and  the  like. 


TaUe  of  the  Chemical  Composition  of  the  Urine  (modified  from  Becquerel). 


967 
14.230 


10-635 


Water        .       .  .       .  . 

Urea  

Other  nitrogenous  crystalline  bodies — 

Uric  acid,  principally  in  the  form  of  alkaline 

urates,  a  trace  only  free. 
Kreatinin,  xanthin,  hypoxanthin. 
Hippuric  acid,  leucin,  tyrosin,  taurin,  cys- 
tin,  etc.,  all  in  small  amounts  and  not 
constant. 
Mucus  and  pigment. 

Salts  :— 

Inorganic — 

Principally  sulphates,  phosphates,  and  chlo- 
rides of  sodium,  and  potassium,  with  phos- 
phates of  magnesium  and  calcium,  traces 
of  silicates  and  of  chlorides. 

Organic — 

Lactates,  hippurates,  acetates  and  formates, 
which  only  appear  occasionally. 

Sugar       .   a  trace  sometimes. 

Gases  (nitrogen  and  carbonic  acid  principally). 


8-135 


1000 


Reaction  of  the  Urine — The  normal  reaction  of  the  urine  is 
slightly  acid.    This  acidity  is  due  to  acid  phosphate  of  sodium,  and  is 


356 


HAND-BOOK  OF  PHYSIOLOGY. 


less  marked  after  meals.  The  urine  contains  no  appreciable  amount  of 
free  acid,  as  it  gives  no  precipitate  with  sodium  hyposulphite.  After 
standing  for  some  time  the  acidity  increases  from  a  kind  of  fermentation, 
due  in  all  probaljility  to  the  presence  of  mucus,  and  acid  urates  or  free 
uric  acid  is  deposited.  After  a  time,  varying  in  length  according  to  the 
temperature,  the  reaction  becomes  strongly  alkaline  from  the  change  of 
urea  into  ammonium  carbonate- — while  at  the  same  time  a  strong  ammoni- 
acal  and  foetid  odor  appears,  with  deposits  of  triple  phosphates  and  alka- 
line urates.  As  this  does  not  occur  unless  the  urine  is  exposed  to  the 
air,  or,  at  least,  until  air  has  had  access  to  it,  it  is  probable  that  the  de- 
composition is  due  to  atmospheric  germs. 

Reaction  of  Urine  iyi  different  classes  of  Animals. — In  most  herbivo- 
rous animals  the  urine  is  alkaline  and  turbid.  The  difference  depends, 
not  on  any  peculiarity  in  the  mode  of  secretion,  but  on  the  differences  in 
the  food  on  which  the  two  classes  subsist:  for  when  carnivorous  animals, 
such  as  dogs,  are  restricted  to  a  vegetable  diet,  their  urine  becomes  pale, 
turbid,  and  alkaline,  like  that  of  an  herbivorous  animal,  but  resumes  its 
former  acidity  on  the  return  to  an  animal  diet;  while  the  urine  voided  by 
herbivorous  animals,  e.g.,  rabbits,  fed  for  some  time  exclusively  upon 
animal  substances,  presents  the  acid  reaction  and  other  qualities  of  the 
urine  of  Carnivora,  its  ordinary  alkalinity  being  restored  only  on  the 
substitution  of  a  vegetable  for  the  animal  diet.  Human  urine  is  not 
usually  rendered  alkaline  by  vegetable  diet,  but  it  becomes  so  after  the 
free  use  of  alkaline  medicines,  or  of  the  alkaline  salts  with  carbonic  or 
vegetable  acids;  for  these  latter  are  changed  into  alkaline  carbonates  pre- 
vious to  elimination  by  the  kidneys. 


Average  quaittitt  of  the  chief  coiTSTiTUEKTS  of  the  Urii^e 

EXCRETED  IJ^"  24  HOURS  BY  HEALTHY  MALE  ADULTS  (PaRKES). 

Water  52*    fluid  ounces. 

Urea       .       .       .       .       .       .       .    512*4  grains. 


Uric  acid  .... 

8-5 

Hippuric  acid,  uncertain        probably  10  to  15  * 

Sulphuric  acid 

.  31-11 

Phosphoric  acid 

.  45- 

Potassium,  Sodium,  Ammonium  Chlorides  )  o^o  9- 
and  free  Chlorine         .       .       .         I  zo 

Lime  ..... 

3-5 

Magnesia  .... 

3- 

Mucus  ..... 

7- 

r  Kreatinin 

Extractives  \  ^'^^'"f 

1  Aanthm 

.  154- 

[  llypoxanthin 
Resinous  matter,  etc. 


Variations  in  Quantity  of  Constituents. — From  these  proportions, 

however,  most  of  the  (constituents  are,  even  in  health,  liable  to  variations. 


THE  KIDNEYS  AND  URINE. 


357 


The  variations  of  the  water  in  different  seasons,  and  according  to  tlie 
quantity  of  drink  and  exercise,  have  already  been  mentioned.  The  water 
of  the  urine  is  also  liable  to  be  influenced  by  the  condition  of  the  nervous 
system,  being  sometimes  greatly  increased  in  hysteria,  and  some  other 
nervous  affections;  and  at  other  times  diminished.  In  some  diseases  it  is 
enormously  increased;  and  its  increase  may  be  either  attended  with  an  aug- 
mented quantity  of  solid  matter,  as  in  ordinary  diabetes,  or  may  be  nearly 
the  sole  change,  as  in  the  affection  termed  diabetes  insipidus.  In  other 
diseases,  e.g.,  the  various  forms  of  albuminuria,  the  quantity  may  be  con- 
siderably diminished.  A  febrile  condition  almost  always  diminishes  the 
quantity  of  water;  and  a  like  diminution  is  caused  by  any  affection  which 
draws  off  a  large  quantity  of  fluid  from  the  body  through  any  other  chan- 
nel than  that  of  the  kidneys,  e.g.,  the  bowels  or  the  skin. 

Method  of  estimating  the  Solids. — A  useful  rule 'for  approximately 
estimating  the  total  solids  in  any  given  specimen  of  healthy  urine  is  to 
multiply  the  last  two  figures,  representing  the  specific  gravity  by  2-33. 
Thus,  in  urine  of  sp.  gr.  1025,  2*33  X  25  =  58 '25  grains  of  solids,  are  con- 
tained in  1000  grains  of  the  urine.  In  using  this  method  it  must  be 
remembered  that  the  limits  of  error  are  much  wider  in  diseased  than  in 
healthy  urine. 

Variations  in  the  Specific  Gravity.— The  specific  gravity  of  the 
human  urine  is  about  1020.  Probably  no  other  animal  fluid  presents  so 
many  varieties  in  density  within  twenty-four  hours  as  the  urine  does;  for 
the  relative  quantity  of  water  and  of  solid  constituents  of  which  it  is 
composed  is  materially  influenced  by  the  condition  and  occupation  of  the 
body  during  the  time  at  which  it  is  secreted,  by  the  length  of  time  which 
has  elapsed  since  the  last  meal,  and  by  several  other  accidental  circum- 
stances. The  existence  of  these  causes  of  difference  in  the  composition 
of  the  urine  has  led  to  the  secretion  being  described  under  the  three  heads 
of  itrina  sanguinis,  urina  potus,  and  urina  cihi.  The  first  of  these 
names  signifies  the  urine,  or  that  part  of  it  which  is  secreted  from 
the  blood  at  times  in  which  neither  food  nor  drink  has  been  recently 
taken,  and  is  applied  especially  to  the  urine  which  is  evacuated  in  the 
morning  before  breakfast.  The  term  urina  potus  indicates  the  urine 
secreted  shortly  after  the  introduction  of  any  considerable  quantity  of 
fluid  into  the  body:  and  the  urina  cihi,  the  portions  secreted  during  the 
period  immediately  succeeding  a  meal  of  solid  food.  The  last  kind  con- 
tains a  larger  quantity  of  solid  matter  than  either. of  the  others;  the  first 
or  second,  being  largely  diluted  with  water,  possesses  a  comparatively 
low  specific  gravity.  Of  these  three  kinds,  the  morning  urine  is  the  best 
calculated  for  analysis  in  health,  since  it  represents  the  simple  secretion 
unmixed  with  the  elements  of  food  or  drink;  if  it  be  not  used,  the  whole 
of  the  urine  passed  during  a  period  of  twenty-four  hours  should  be  taken. 


358 


HAND-BOOK  OF  PHYSIOLOGY. 


In  accordance  Avith  the  various  circumstances  above-mentioned,  the 
specitic  gravity  of  the  urine  may,  consistently  with  health,  range  widely 
on  both  sides  of  the  usual  average.  The  average  healthy  range  may  be 
stated  at  from  1015  in  the  winter  to  10"-25  in  the  summer;  but  variations 
of  diet  and  exercise,  and  many  other  circumstances,  may  make  even  greater 
differences  than  these.  In  disease,  the  variation  may  be  greater;  some- 
times descending,  in  albuminuria,  to  1004,  and  frequently  ascending  in 
diabetes,  when  the  urine  is  loaded  with  sugar,  to  1050,  or  even  to  1060. 

Quantity. — The  total  quantity  of  urine  passed  in  twenty-four  hottrs 
is  affected  by  numerous  circumstances.  On  taking  the  mean  of  many 
observations  by  several  experimenters,  the  average  quantity  voided  in 
twenty-four  hours  by  healthy  male  adults  from  20  to  40  years  of  age  has 
been  found  to  amottnt  to  about  52 J  fluid  ounces  (1-|  to  2  litres). 

Abnormal  Constituents. — In  disease,  or  after  the  ingestion  of 
special  foods,  various  abnormal  substances  occur  in  urine,  of  which  the 
following  may  be  mentioned — serum-albumin,  globulin,  ferments  (ap- 
parently present  in  health  also),  blood,  sugar,  bile  acids,  and  pigments, 
fats,  oxalates,  various  salts  taken  as  medicine,  and  other  matters,  as  bac- 
teria and  renal  casts. 


The  Solids  of  the  Ueixe. 


Urea  (CH^]N".,0). — Urea  is  the  principal  solid  constitttent  of  the 
urine,  forming  nearly  one-half  of  the  whole  qtiantity  of  solid  matter.  It 
is  also  the  most  important  ingredient,  since  it  is  the  chief  substance  by 
which  the  nitrogen  of  decomposed  tissue  and  superfluous  food  is  excreted 

from  the  body.  For  its  removal,  the  secre- 
tion of  urine  seems  especially  provided;  and 
by  its  retention  in  the  blood  the  most  per- 
nicious effects  are  produced. 

Properties. — Urea,  like  the  other  solid 
constituents  of  the  urine,  exists  in  a  state 
of  solution.  But  it  may  be  procured  in  the 
solid  state,  and  then  appears  in  the  form  of 
delicate  silvery  acicular  crystals,  which, 
under  the  microscope,  appear  as  four-sided 
prisms  (Fig.  2-4T).  It  is  obtained  in  this 
state  by  evaporating  urine  carefully  to  the 
consistence  of  honey,  acting  on  the  inspis- 
sated mass  with  four  parts  of  alcohol,  then  evaporating  the  alcoholic 
solution,  and  ]nirifying  the  residue  by  repeated  solution  in  water  or  alco- 
hol, and  linally  allowing  it  to  crystallize.  It  readily  combines  with 
some  acids,  like  a  weak  base;  and  may  thus  be  conveniently  procured 
in  tlu'  form  of  crvstals  of  nitrate  or  oxalate  of  urea. 


Fig.  247.— Crj-stals  of  Urea. 


THE  KIDNEYS  AND  URINE. 


359 


Urea  is  colorless  when  pure;  when  impure,  yellow  or  hrown:  without 
smell,  and  of  a  cooling  nitre-like  taste;  has  neither  an  acid  nor  an  alka- 
line reaction,  and  deliquesces  in  a  moist  and  warm  atmosphere.  At  59°  F. 
(15*^  C.)  it  requires  for  its  solution  less  than  its  weight  of  water;  it  is 
dissolved  in  all  proportions  by  boiling  water;  but  it  requires  five  times  its 
weight  of  cold  alcohol  for  its  solution.  It  is  insoluble  in  ether.  At  248°  F. 
(120°  C.)  it  melts  without  undergoing  decomposition;  at  a  still  higher 
temperature  ebullition  takes  place,  and  carbonate  of  ammonium  sublimes; 
the  melting  mass  gradually  acquires  a  pulpy  consistence;  and  if  the  heat 
is  carefully  regulated,  leaves  a  grey-white  powder,  cyanic  acid. 

Chemical  Nature  of  Urea. — The  chemical  nature  of  urea  is  ex- 
plained elsewhere,'  but  it  will  be  as  well  to  mention  here  that  urea  is 
isomeric  with  ammonium  cyanate,  and  that  it  was  first  artificially  pro- 
duced from  this  substance.  Thus: — Ammonium  cyanate  (NH^.C^N'O) 
=  urea  (CH^l^^^).  The  action  of  heat  upon  urea  in  evolving  ammonium 
carbonate  and  leaving  cyanic  acid,  is  thus  explained.  A  similar  de- 
composition of  the  urea  with  development  of  ammonium  carbonate 
ensues  spontaneously  when  urine  is  kept  for  some  days  after  being  voided, 
and  explains  the  ammoniacal  odor  then  evolved  (p.  356).  The  urea  is  some- 
times decomposed  before  it  leaves  the  bladder,  when  the  mucous  mem- 
brane is  diseased,  and  the  mucus  secreted  by  it  is  both  more  abundant, 
and,  probably,  more  prone  to  act  as  a  ferment;  although  the  decomposi- 
tion does  not  often  occur  unless  atmospheric  germs  have  had  access  to 
the  urine. 

Variations  in  the  Quantity  of  Urea. — The  quantity  of  urea  ex- 
creted is,  like  that  of  the  urine  itself,  subject  to  considerable  variation. 
For  a  healthy  adult  500  grains  (about  32-5  grms.)  per  diem  maybe  taken 
as  rather  a  high  average.  Its  percentage  in  healthy  urine  is  1*5  to  2  "5. 
It  is  materially  influenced  by  diet,  being  greater  when  animal  food  is  ex- 
clusively used,  less  when  the  diet  is  mixed,  and  least  of  all  with  a  vegeta- 
ble diet.  As  a  rule,  men  excrete  a  larger  quantity  than  women,  and  per- 
sons in  the  middle  periods  of  life  a  larger  quantity  than  infants  or  old 
people.  The  quantity  of  urea  excreted  by  children,  relatively  to  their 
body-weight,  is  much  greater  than  in  adults.  Thus  the  quantity  of  urea 
excreted  per  kilogram  of  weight  was,  in  a  child,  0  '8  grm. :  in  an  adult 
only  0*4  grm.  Eegarded  in  this  way,  the  excretion  of  carbonic  acid 
gives  similar  result,  the  proportion  in  the  child  and  adult  being  as  82  : 34. 

The  quantity  of  urea  does  not  necessarily  increase  and  decrease  with 
that  of  the  urine,  though  on  the  whole  it  would  seem  that  whenever  the 
amount  of  urine  is  much  augmented,  the  quantity  of  urea  also  is  usually 
increased;  and  it  appears  that  the  quantity  of  urea,  as  of  urine,  may  be 
especially  increased  by  drinking  large  quantities  of  water.    In  various 


'  Appendix. 


360 


HAND-BOOK  OF  PHYSIOLOGY. 


diseases  the  quantity  is  reduced  considerably  below  the  healthy  standard, 
while  in  other  affections  it  is  above  it. 

Estimation  of  Urea. — A  convenient  apparatus  for  estimating  the 
quantity  of  urea  in  a  given  sample  of  urine  is  that  devised  by  Eussell  and 
West. 

Urea  contains  nearly  half  its  weight  of  nitrogen;  hence  this  gas  may 
be  taken  as  a  measure  of  the  urea.  A  small  quantity  of  urine  is  mixed 
with  a  large  excess  of  solution  of  sodium  hypobromite,  which  completely 
decomposes  the  urea,  liberating  all  the  nitrogen  in  a  gaseous  form:  a 
gentle  heat  promotes  the  reaction.  The  percentage  of  urea  can  of  course 
be  readily  calculated  from  the  volume  of  nitrogen  evolved  from  a  measured 
quantity  of  the  urine,  but  this  calculation  is  avoided  by  graduating  the 
tube  in  which  the  nitrogen  is  collected  with  numbers  which  indicate  the 
corresponding  percentage  of  urea.  -\-  3NaBrO  +  2NaH0  = 

3NaBr  +  3H,0  +  mfiO,  +  IST,. 

Uric  Acid  (C^H^N^Og). — This  substance,  which  was  formerly  termed 
lithic  acid,  on  account  of  its  existence  in  many  forms  of  urinary  calculi, 
is  rarely  absent  from  the  urine  of  man  or  animals,  though'in  the  feline 
tribe  it  seems  to  be  sometimes  entirely  replaced  by  urea.  The  jDro- 
portionate  quantity  of  uric  acid  varies  considerably  in  different  animals. 
In  man,  and  Mammalia  generally,  especially  the  Herbivora,  it  is  com- 
paratively small.  In  the  whole  tribe  of  birds,  and  of  serpents,  on  the 
other  hand,  the  quantity  is  very  large,  greatly  exceeding  that  of  the  urea. 
In  the  urine  of  granivorous  birds,  indeed,  urea  is  rarely  if  ever  found,  its 
place  being  entirely  supplied  by  uric  acid. 

Variations  in  Quantity. — The  quantity  of  uric  acid,  like  that  of 
urea,  in  human  urine,  is  increased  by  the 'use  of  animal  food,  and  de- 
creased by  the  use  of  food  free  from  nitrogen,  or  by  an  exclusively  vege- 
table diet.  In  most  febrile  diseases,  and  in  plethora,  it  is  formed  in  un- 
naturally large  quantities;  and  in  gout  it  is  deposited  in,  and  around, 
joints,  in  the  form  of  urate  of  soda,  of  which  the  so-called  clialk-stones 
of  this  disease  are  principally  composed.  The  average  amount  secreted 
in  twenty-four  hours  is  8*5  grains  (rather  more  than  half  a  gramme). 

Condition  of  Uric  Acid  in  the  Urine. — The  condition  in  which 
uric  acid  exists  in  solution  in  the  urine  has  formed  th3  subject  of  some 
discussion,  because  of  its '  difficult  solubility  in  water.  It  is  found  chiefly 
in  the  form  of  urate  of  sodium,  produced  by  the  uric  acid  as  soon  as  it  is 
formed,  combining  with  part  of  tlie  base  of  the  alkaline  sodium  phosphate 
of  tlie  blood.  Ilippuric  acid,  wliich  exists  in  human  urine  also,  acts  upon 
the  alkaline  phosphate  in  tlie  same  way,  and  increases  still  more  the  quan- 
tity of  acid  phosphate,  on  the  presence  of  which  it  is  probable  tliat  a  part 
of  the  natural  acidity  of  the  urine  depends.  It  is  scarcely  possible  to  say 
whether  the  union  of  uric  acid  with  the  base  sodium  and  probably  ammo- 
nium, takes  place  in  the  blood,  or  in  the  act  of  secretion  in  the  kidney: 


THE  KIDNEYS  AND  URINE. 


361 


the  latter  is  the  more  likely  opinion;  but  the  quantity  of  either  uric  acid 
or  urates  in  the  blood  is  probably  too  small  to  allow  of  this  question  being 
solved. 

Owing  to  its  existence  in  combination  in  healthy  urine,  uric  acid  for 
examination  must  generally  be  precipitated  from  its  bases  by  a  stronger 
acid.  Frequently,  however,  when  excreted  in  excess,  it  is  deposited  in  a 
crystalline  form  (Fig.  248),  mixed  with  large  quantities  of  ammonium  or 
sodium  urate.  In  such  cases  it  may  be  procured  for  microscopic  exami- 
nation by  gently  warming  the  portion  of  urine  containing  the  sediment; 
this  dissolves  urate  of  ammonium  and  sodium,  while  the  comparatively 
insoluble  crystals  of  uric  acid  subside  to  the  bottom. 

The  most  common  form  in  which  uric  acid  is  deposited  in  urine,  is  that 
of  a  brownish  or  yellowish  powdery  substance,  consisting  of  granules  of 


FiGF.  248.— Various  forms  of  uric  acid  crystals.  Fig.  249.— Crystals  of  hippuric  acid. 

ammonium — or  sodium  urate.  When  deposited  in  crystals,  it  is  most 
frequently  in  rhombic  or  diamond-shaped  laminae,  but  other  forms  are  not 
uncommon  (Fig.  248).  When  deposited  from  the  urine,  the  crystals  are 
generally  more  or  less  deeply  colored,  from  being  combined  with  the 
coloring  principles  of  the  urine. 

There  are  two  chief  tests  for  uric  acid  besides  the  microscopic  evidence 
of  its  crystalline  structure:  (1)  The  Murexide  test,  which  consists  of 
evaporating  to  dryness  a  mixture  of  strong  nitric  acid  and  uric  acid  in  a 
water  bath.  This  leaves  a  yellowish-red  residue  of  Alloxan  (C^H^N^OJ 
and  urea,  and  this,  on  addition  of  ammonium  hydrate,  gives  a  beautiful 
purple  (ammonium  purpurate,  OgH^  (NHJ  N^Og),  deepened  on  addition 
of  caustic  potash.  (2)  Scliiff's  test.  Dissolve  the  uric  acid  in  sodium 
carbonate  solution,  and  drop  some  of  it  on  a  filter  paper  moistened  with 
silver  nitrate,  a  black  spot  appears,  which  corresponds  to  the  reduction 
of  silver  by  the  uric  acid. 

Hippuric  Acid  (CgHgNOg)  has  long  been  known  to  exist  in  the  urine 
of  herbivorous  animals  in  combination  with  soda.    It  also  exists  naturally 


362 


HAND-BOOK  OF  PHYSIOLOGY. 


in  the  urine  of  man,  in  quantity  equal  or  rather  exceeding  that  of  the 
uric  acid. 

Pigments. — The  coloring  matters  of  the  urine  are:  (1)  Uro-biIi?i, 
a  substance  connected  with  the  coloring  matters  of  the  blood  and  bile 
(p.  275);  it  is  especiall}^  seen  in  febrile  urine  and  exists  normally,  but 
to  less  amount;  it  is  of  a  yellowish-red  color;  (2)  Uro-chrome,  which  on 
exposure  undergoes  oxidation,  and  becomes  Uro-erytlirin,  the  former 
being  yellowish  and  the  latter  sandy  red;  and  (3)  Indican  is  occasionally 
present. 

Indican  is  not  itself  pigmentary,  though  by  its  decomposition  indigo 
blue  and  indigo  red  are  produced.  Its  presence  can  usually  be  detected 
by  adding  to  a  small  quantity  of  urine  an  equal  bulk  of  strong  hydrochloric 
acid,  and  gently  heating  the  solution;  on  the  addition  of  two  or  three 
drops  of  strong  nitric  acid  a  delicate  purplish  tint  is  developed,  and  indigo 
blue  and  red  crystals  separate  out. 

Mucus. — JIucKS  in  the  urine  consists  principally  of  the  epithelial 
debris  of  the  mucous  surface  of  the  urinary  passages.  Particles  of  epithe- 
lium, in  greater  or  less  abundance,  may  be  detected  in  most  samples  of 
urine,  especially  if  it  has  remained  at  rest  for  some  time  and  the  lower 
strata  are  then  examined  (Fig.  250).    As  urine  cools,  the  mucous  is  some- 


times seen  suspended  in  it  as  a  delicate  opaque  cloud,  but  generally  it 
falls.  In  inflammatory  affections  of  the  urinary  passages,  especially  of 
the  bladder,  mucus  in  large  quantities  is  poured  forth,  and  speedily  un- 
dergoes decomposition.  The  presence  of  the  decomposing  mucus  excites 
(as  already  stated,  p.  356)  chemical  changes  in  the  urea,  whereby  ammo- 
nia, or  carbonate  of  ammonium,  is  formed,  which,  combining  with  the 
excess  of  acid  in  the  super-phosphates  in  the  urine,  produces  insoluble 
neutral  or  alkaline  phosphates  of  calcium  and  magnesium,  and  phosphate 
of  ammonium  and  magnesium.  These  mixing  witli  the  mucus,  constitute 
tlie  peculiar  white,  viscid,  mortar-like  substance  which  collects  upon  the 
mucous  surface  of  the  bladder,  and  is  often  passed  with  the  urine,  form- 
ing a  thick  tenacious  sediment. 


Fig.  250.— 3Iucus  deposited  from  urine. 


THE  KIDNEYS  AND  URINE. 


363 


Extractives. — Besides  mucus  and  coloring  matter,  urine  contains  a 
considerable  quantity  of  nitrogenous  compounds,  usually  described  under 
the  generic  name  of  extractives.  Of  these,  the  chief  are:  (1)  Kreatinin 
(O^H^lSTgO)  a  substance  derived,  probably,  from  the  metamorphosis  of  mus- 
cular tissue,  crystallizing  in  colorless  oblique  rhombic  prisms;  a  fairly 
definite  amount  of  this  substance,  about  15  grains  (1  grm.),  appears  in 
the  urine  daily,  so  that  it  must  be  looked  upon  as  a  normal  constituent;  it 
is  increased  on  an  increase  of  the  nitrogenous  constituents  of  the  food; 
(2)  Xanthin  (O^N^H^OJ,  an  amorphous  powder  soluble  in  hot  water;  (3) 
Hypo-xantJiin,  or  sarkin  (O^N^H^O);  (4)  Oxaluric  acid  {QJl^Jd^  in 
combination  with  ammonium;  (5)  Allantoin  (O^HgN^Og),  in  the  urine 
of  the  new-born  child.  All  these  extractives  are  chiefly  interesting  as 
being  closely  connected  with  urea,  and  mostly  yielding  that  substance  on 
oxidation.  Leucin  and  tyrosin  can  scarcely  be  looked  upon  as  normal 
constituents  of  urine. 

Saline  Matter. — The  sulphuric  acid  in  the  urine  is  combined  chiefly 
or  entirely  with  sodium  or  potassium;  forming  salts  which  are  taken  in 
very  small  quantity  with  the  food,  and  are  scarcely  found  in  other  fluids 
or  tissues  of  the  body;  for  the  sulphates  commonly  enumerated  among 
the  constituents  of  the  ashes  of  the  tissues  and  fluids  are  for  the  most 
part,  or  entirely,  produced  by  the  changes  that  take  place  in  the  burn- 
ing. Only  about  one-third  of  the  sulphuric  acid  found  in  the  urine  is 
derived  directly  from  the  food  (Parkes).  Hence  the  greater  part  of  the 
sulphuric  acid  which  the  sulphates  in  the  urine  contain,  must  be  formed 
in  the  blood,  or  in  the  act  of  secretion  of  urine;  the  sulphur  of  which  the 
acid  is  formed  being  probably  derived  from  the  decomposing  nitrogenous 
tissues,  the  other  elements  of  which  are  resolved  into  urea  and  uric  acid. 
It  may  be  in  part  derived  also  from  the  sulphur-holding  taurin  and 
cystin,  which  can  be  found  in  the  liver,  lungs,  and  other  parts  of  the 
body,  but  not  generally  in  the  excretions;  and  which,  therefore,  must  be 
broken  up.  The  oxygen  is  supplied  through  the  lungs,  and  the  heat  gen- 
erated during  combination  with  the  sulphur,  is  one  of  the  subordinate 
means  by  which  the  animal  temperature  is  maintained. 

Besides  the  sulphur  in  these  salts,  some  also  appears  to  be  in  the  urine, 
uncombined  with  oxygen;  for  after  all  the  sulphates  have  been  re- 
moved from  urine,  sulphuric  acid  may  be  formed  by  drying  and  burning 
it  with  nitre.  From  three  to  five  grains  of .  sulphur  are  thus  daily  ex- 
creted. The  combination  in  which  it  exists  is  uncertain:  possibly  it  is  in 
some  compound  analogous  to  cystin  or  cystic  oxide  (p.  365).  Sulphuric 
acid  also  exists  normally  in  the  urine  in  combination  with  phenol 
(CgHgO)  as  phenol  sulphuric  acid  or  its  corresponding  salts,  with 
sodium,  etc. 

The  phosphoric  acid  in  the  urine  is  combined  partly  with  the  alkalies, 
partly  with  the  alkaline  earths — about  four  or  five  times  as  much  with 


364 


HAND-BOOK  OF  PHYSIOLOGY. 


the  former  as  with  the  latter.  In  blood,  saliva,  and  other  alkaline  fluids 
of  the  body,  phosphates  exist  in  the  form  of  alkaline,  neutral,  or  acid 
salts.  In  the  urine  they  are  acid  salts,  viz.,  the  sodium,  ammonium, 
calcium,  and  magnesium  phosphates,  the  excess  of  acid  being  (Liebig) 
due  to  the  appropriation  of  the  alkali  with  which  the  phosphoric  acid  in 
the  blood  is  combined,  by  the  several  new  acids  which  are  formed  or  dis- 
charged at  the  kidneys,  namely,  the  uric,  hippuric,  and  sulphuric  acids, 
all  of  which  are  neutralized  with  soda. 

The  phosphates  are  taken  largely  in  both  vegetable  and  animal  food; 
some  thus  taken  are  excreted  at  once;  others,  after  being  transformed 
and  incorporated  with  the  tissues.  Calcium  phosphate  forms  the  prin- 
cipal earthy  constituent  of  bone,  and  from  the  decomposition  of  the  osse- 
ous tissue  the  urine  derives  a  large  quantity  of  this  salt.  The  decompo- 
sition of  other  tissues  also,  but  especially  of  the  brain  and  nerve-sub- 
stance, furnishes  large  supplies  of  phosphorus  to  the  urine,  which 


Fig.  251.— Urinary  sediment  of  triple  phosphates  (large  prismatic  crystals)  and  urate  of  am- 
monimn,  from  m-ine  which  had  undergone  alkaline  fermentation. 


phosphorus  is  supposed,  like  the  sulphur,  to  be  united  with  oxygen,  and 
then  combined  with  bases.  This  quantity  is,  however,  liable  to  consid- 
erable variation.  Any  undue  exercise  of  the  brain,  and  all  circumstances 
producing  nervous  exhaustion,  increase  it.  The  earthy  phosphates  are 
more  abundant  after  meals,  whether  on  animal  or  vegetable  food,  and  are 
diminished  after  long  fasting.  The  alkaline  phosphates  are  increased 
after  animal  food,  diminished  after  vegetable  food.  Exercise  increases 
the  alkaline,  but  not  the  earthy  phosphates  (Bence  Jones).  Phosphorus 
uncombined  with  oxygen  appears,  like  sulphur,  to  be  excreted  in  the 
urine  (Ronalds).  When  the  urine  undergoes  alkaline  fermentation, 
phosphates  are  deposited  in  the  form  of  a  urinary  sediment,  consisting 
chiefly  of  ammonio-magnesium  phosphate  (triple  phosphate)  (Fig.  251). 
This  compound  does  not,  as  such,  exist  in  healtliy  urine.  The  ammonia 
is  chicily  or  wholly  derived  from  the  decomposition  of  urea  (p.  359). 

Tlie  chlorine  of  the  urine  occurs  chiefly  in  combination  with  sodium, 
but  slightly  also  witli  ammonium,  and  perhaps  potjissium.    As  the  chlo- 


THE  KIDNEYS  AND  URINE. 


365 


rides  exist  largely  in  food  and  in  most  of  the  animal  fluids,  their  occur- 
rence in  the  urine  is  easily  understood. 

Cystin  (CgH^^s^SOJ  (Fig.  252)  is  an  occasional  constituent  of  urine. 
It  resembles  taurin  in  containing  a  large  quantity  of  sulphur — more  than 
25  per  cent.    It  does  not  exist  in  healthy  urine. 

Another  common  morbid  constituent  of  the  urine  is  oxalic  acid,  which 
is  frequently  deposited  in  combination  with  calcium  (Fig.  253)  as  a 


Fig.  252.— Crystals  of  cystin.  Fia.  253.— Crystals  of  calcium  oxalate. 


urinary  sediment.  Like  cystin,  but  much  more  commonly,  it  is  the  chief 
constituent  of  certain  calculi. 

Of  the  other  abnormal  constituents  of  the  urine  mentioned  it  will  be 
unnecessary  to  speak  at  length  in  this  work. 

Gases. — A  small  quantity  of  gas  is  naturally  present  in  the  urine  in 
a  state  of  solution.  It  consists  of  carbonic  acid  (chiefly)  and  nitrogen 
and  a  small  quantity  of  oxygen. 

The  Method  of  the  Exceetioj^"  op'IIeixe. 

The  excretion  of  the  urine  by  the  kidney  is  believed  to  consist  of  two 
more  or  less  distinct  processes — viz.,  (1.)  of  filtratioii,  by  which  the  water 
and  the  ready-formed  salts  are  eliminated;  and  (2.)  of  true  secretion,  by 
which  certain  substances  forming  the  chief  and  more  important  part  of 
the  urinary  solids  are  removed  from  the  blood.  This  division  of  function 
corresponds  more  or  less  to  the  division  in  the  functions  of  other  glands 
of  which  we  have  already  treated.  It  will  be  as  well  to  consider  them 
separately. 

(1.)  Of  Filtration. — This  part  of  the  renal  function  is  performed 
within  the  Malpighian  corpuscles  by  the  renal  glomeruli.  By  it  not  only 
the  water  is  strained  off,  but  also  certain  other  constituents  of  the 
urine,  e.g.,  sodium  chloride,  are  separated.  The  amount  of  the  fluid 
filtered  off  depends  almost  entirely  upon  the  blood-pressure  in  the 
glomeruli. 


366 


HAND-BOOK  OF  PHYSIOLOGY. 


The  greater  the  blood-pressure  in  the  arterial  system  generally,  and 
consequently  in  the  renal  arteries,  the  greater,  cmteris  paribus,  will  be 
the  blood-pressure  in  the  glomeruli,  and  the  greater  the  quantity  of  urine 
separated;  but  even  without  increase  of  the  general  blood-pressure,  if  the 
renal  arteries  be  locally  dilated,  the  pressure  in  the  glomeruli  will  be 
increased  and  with  it  the  secretion  of  urine.  On  the  other  hand,  if  the 
local  blood-pressure  be  diminished,  the  amount  of  fluid  will  be  lessened. 
All  the  numerous  causes,  therefore,  which  increase  the  blood-pressure  (p. 
152)  will,  as  a  rule,  secondarily  increase  the  secretion  of  urine.  Of  these 
the  hearths  action  is  amongst  the  most  important.  When  its  contractions 
are  increased  in  force,  increased  diuresis  is  the  result.  Similarly,  causes 
which  lower  the  blood-pressure,  e.g.,  enfeebled  action  of  the  heart,  great 
loss  of  blood,  etc.,  will  diminish  the  activity  of  the  secretion  of  urine. 

The  close  connection  between  the  blood-pressure  generally  and  the 
nervous  system  has  been  before  considered,  and  it  will  be  clear,  therefore, 
that  the  amount  of  urine  secreted  depends  greatly  upon  the  influence  of 
the  nervous  system.  Thus,  division  of  the  spinal  cord,  by  producing 
general  vascular  dilatation,  causes  a  great  diminution  of  blood-pressure, 
and  so  diminishes  the  amount  of  water  passed;  since  the  local  dilatation 
in  the  renal  arteries  is  not  sufficient  to  counteract  the  general  diminution 
of  pressure.  Stimulation  of  the  cut  cord  produces,  strangely  enough, 
the  same  results — i.e.,  a  diminution  in  the  amount  of  the  urine  passed, 
but  in  a  different  way,  viz.,  by  constricting  the  arteries  generally,  and, 
among  others,  the  renal  arteries;  the  diminution  of  blood-pressure  result- 
ing from  the  local  resistance  in  the  renal  arteries  being  more  potent  to 
diminish  blood-pressure  in  the  glomeruli  than  the  general  increase  of 
blood-pressure  is  to  increase  it.  Section  of  the  renal  nerves  or  of  any 
others  which  produce  local  dilatation  without  greatly  diminishing  the 
general  blood-pressu're  will  cause  an  increase  in  the  quantity  of  fluid 
passed. 

The  fact  that  in  summer  or  in  hot  weather  the  urine  is  diminished 
may  be  attributed  partly  to  the  copious  elimination  of  water  by  the  skin 
in  the  form  of  sweat  which  occurs  in  summer,  as  contrasted  with  the 
greatly  diminished  functional  activity  of  the  skin  in  winter,  but  also  to 
the  dilated  condition  of  the  vessels  of  the  skin  causing  a  decrease  in  the 
general  blood-pressure.  Thus  we  see  that  in  regard  to  the  elimination 
of  water  from  the  system,  the  skin  and  kidneys  perform  similar  functions, 
and  are  capable  to  some  extent  of  acting  vicariously,  one  for  the  other. 
Their  relative  activities  are  inversely  proportional  to  each  other. 

The  intimate  connection  between  the  condition  of  the  kidney  and  the 
])lood-pressure  has  been  exceedingly  well  shown  by  the  introduction  of  an 
instrument  called  tlie  Oncometer,  recently  introduced  by  Roy,  whicli  is  a 
modification  of  the  plethysmograph  (Fig.  138).  By  means  of  this  a})pa- 
ratus  any  alteration  in  the  volume  of  the  kidney  is  communicated  to  an 


THE  KIDNEYS  AND  UKINE. 


367 


apparatus  (oncograph)  capable  of  recording  graphically,  with  a  writing 
lever,  such  variations.  It  has  been  found  that  the  kidney  is  extremely 
sensitive  to  any  alteration  in  the  general  blood-pressure,  every  fall  in  the 
general  blood-pressure  being  accompanied  by  a  decrease  in  the  volume  of 
the  kidney,  and  every  rise,  unless  produced  by  considerable  constriction 
of  the  peripheral  vessels,  including  those  of  the  kidney,  being  accompanied 
by  a  corresponding  increase  of  volume.  Increase  of  volume  is  followed 
by  an  increase  in  the  amount  of  urine  secreted,  and  decrease  of  volume 
by  a  decrease  in  the  secretion.  In  addition,  however,  to  the  response  of 
the  kidney  to  alterations  in  the  general  blood-pressure,  it  has  been  fur- 
ther observed  that  certain  substances,  when  injected  into  the  blood,  will 
also  produce  an  increase  in  volume  of  the  kidney,  and  consequent  increased 
flow  of  urine,  without  affecting  the  general  blood-pressure — such  bodies 
as  sodium  acetate  and  other  diuretics.  These  observations  appear  to  prove 
that  local  dilatation  of  the  renal  vessels  may  be  produced  by  alterations 
in  the  blood  upon  a  local  nervous  mechanism,  as  the  effect  is  produced 
when  all  of  the  renal  nerves  have  been  divided.  The  alterations  are  not 
only  produced  by  the  addition  of  drugs,  but  also  by  the  introduction  of 
comparatively  small  quantities  of  water  or  saline  solution.  To  this  altera- 
tion of  the  blood  acting  upon  the  renal  vessels  (either  directly  or)  through 
a  local  vaso- motor  mechanism,  and  not  to  any  great  alteration  in  the 
general  blood-pressure,  must  we  attribute  the  effect  of  meals,  etc.,  ob- 
served by  Eoberts.  '  'The  renal  excretion  is  increased  after  meals  and 
diminished  during  fasting  and  sleep.  The  increase  began  within  the  first 
hour  after  breakfast,  and  continued  during  the  succeeding  two  or  three 
hours;  then  a  diminution  set  in,  and  continued  until  an  hour  or  two  after 
dinner.  The  effect  of  dinner  did  not  appear  until  two  or  three  hours  after 
the  meal;  and  it  reached  its  maximum  about  the  fourth  hour.  From  this 
period  the  excretion  steadily  decreased  until  bedtime.  During  sleep  it 
sank  still  lower,  and  reached  its  minimum — being  not  more  than  one- 
third  of  the  quantity  excreted  during  the  hours  of  digestion. The  in- 
creased amount  of  urine  passed  after  drinking  large  quantities  of  fluid 
probably  depends  upon  the  diluted  condition  of  the  blood  thereby  in- 
duced. 

The  following  table'  will  help  to  explain  the  dependence  of  the  filtra- 
tion function  upon  the  blood-pressure  and  the  nervous  system: — 

Table  of  the  Relation  of  the  Secretion  of  Urine  to  Arterial  Pressure, 

A.  Secretion  of  Urine  may  be  increased — 

a.  By  increasing  the  general  hlood-pressure,  by 

1.  Increase  of  force  or  frequency  of  heart-beat. 

2.  Constriction  of  small  arteries  of  areas  other  than  the  kidney. 


^  Modified  from  M.  Foster. 


368 


HAND-BOOK  OF  PHYSIOLOGY. 


d.  By  relaxation  of  the  renal  artery  ivithout  compensating  relaxa- 
tion elsewhere,  by 

1.  Division  of  the  renal  nerves  (causing  polyuria). 

2.  "  and  afterward  stimulating  cord 
below  medulla  (causing  greater  polyuria). 

3.  Division  of  the  splanchnic  nerves;  but  polyuria  is  less  than 

in  1  or  2^  as  these  nerves  are  distributed  to  a  wider  area, 
the  dilatation  of  the  renal  artery  is  accompanied  by  dila- 
tation of  other  vessels,  and  therefore  with  a  somewhat 
diminished  general  blood  sujoply. 

4.  Puncture  of  the  floor  of  fourth  ventricle  or  mechanical  irri- 

tation of  the  superior  cervical  ganglion  of  the  sympathetic, 
possibly  from  dilatation  of  the  renal  arteries. 

B.  Secretion  of  urine  may  be  diminished — 

a.  By  diminishing  the  general  Uood-presmre,  by 

1.  Diminishing  the  force  or  frequency  of  the  heart-beats. 

2.  Dilatation  of  capillary  areas  other  than  the  kidney. 

3.  Division  of  spinal  cord  below  medulla,  which  causes  dilata- 

tion of  general  abdominal  area,  and  urine  generally  ceases 
being  secreted. 

t.  By  increasing  the  Uood-pressure,  by  stimulation  of  spinal  cord 
below  medulla,  the  constriction  of  the  renal  artery  not  being- 
compensated  for  by  the  increase  of , general  blood-pressure. 

c.  By  constriction  of  the  renal  artery,  by  stimulating  the  renal  or 
splanchnic  nerves,  or  by  stimulating  the  spinal  cord. 

Although  it  is  convenient  to  call  the  processes  which  go  on  in  the  renal 
glomeruli,  filtration,  there  is  reason  to  believe  that  they  are  not  absolutely 
mechanical,  as  the  term  might  seem  to  imply,  since,  when  the  epithelium 
of  the  Malpighian  capsule  has  been,  as  it  were,  put  out  of  order  by  liga- 
ture of  the  renal  artery,  on  removal  of  the  ligature,  the  urine  has  been 
found  temporarily  to  contain  albumen,  indicating  that  a  selective  power 
resides  in  the  healthy  epitlielium,  wdiicli  allows  a  certain  constituent  part 
of  the  blood  to  be  filtered  off  and  not  others. 

(2.)  Of  True  Secretion. — That  there  is  a  second  part  in  the  process 
of  the  excretion  of  urine,  which  is  true  secretion,  is  suggested  by  the 
structure  of  the  tubuli  uriniferi,  and  the  idea  is  supported  by  various 
experiments.  It  will  be  remembered  that  the  convoluted  portions  of  the 
tubules  are  lined  w^ith  epithelium,  wdiich  bears  a  close  resemblance  to  the 
secretory  epithelium  of  other  glands,  whereas  the  Malpigliian  capsules 
and  portions  of  the  loops  of  Ileide  are  lined  simply  by  endothelium.  The 
two  functions  are,  then,  suggested  by  the  differences  of  epithelium,  and 
also  by  the  fact  that  the  blood  supply  is  different,  since  the  convoluted 
tubes  are  surrounded  by  cai)illary  vessels  derived  from  the  breaking  u])  of 
the  efferent  vessels  of  the  Malpigliian  tufts.  The  theory  first  suggested 
by  Bowman  (1842),  and  still  generally  accepted,  of  the  function  of  the 


THE  KIDNEYS  AND  URINE. 


869 


two  parts  of  the  tubules,  is  that  the  cells  of  the  convoluted  tubes,  by  a 
process  of  true  secretion,  separate  from  the  blood  substances  such  as 
urea,  whereas  from  the  glomeruli  are  separated  the  water  and  the  inor- 
ganic salts.  Another  theory  suggested  by  Ludwig  (1844)  is  that  in  the 
glomeruli  is  filtered  off  from  the  blood  all  the  constituents  of  the  urine  in 
a  very  diluted  condition.  When  this  passes  along  the  tortuous  uriniferous 
tube,  part  of  the  water  is  re-absorbed  into  the  vessels  surrounding  them, 
leaving  the  urine  in  a  more  concentrated  condition — retaining  all  its 
proper  constituents.  This  osmosis  is  promoted  by  the  high  specific  gravity 
of  the  blood  in  the  capillaries  surrounding  the  convoluted  tubes,  but  the 
return  of  the  urea  and  similar  substances  is  prevented  by  the  secretory 
epithelium  of  the  tubules.  Ludwig's  theory,  however  plausible,  must, 
we  think,  give  way  to  the  first  theory,  which  is  more  strongly  supported 
by  direct  experiment. 

By  using  the  kidney  of  the  newt,  which  has  two  distinct  vascular  sup- 
plies, one  from  the  renal  artery  to  the  glomeruli,  and  the  other  from  the 
renal  portal  vein  to  the  convoluted  tubes,  Nussbaum  has  shown  that  cer- 
tain substances,  e.g.,  peptones,  sugar,  when  injected  into  the  blood,  are 
eliminated  by  the  glomeruli,  and  so  are  not  got  rid  of  when  the  renal 
arteries  are  tied;  whereas  certain  other  substances,  e.g.,  urea,  when  injected 
iftto  the  blood,  are  eliminated  by  the  convoluted  tubes,  even  when  the 
renal  arteries  have  been  tied.  This  evidence  is  very  direct  that  urea  is 
excreted  by  the  convoluted  tubes. 

Heidenhain  also  has  shown  by  experiment  that  if  a  substance  (sodium 
sulphindigotate),  which  ordinarily  produces  blue  urine,  be  injected  into 
the  blood  after  section  of  the  medulla  which  causes  lowering  of  the  blood- 
pressure  in  the  renal  glomeruli,  that  when  the  kidney  is  examined,  the 
cells  of  the  convoluted  tubules  (and  of  these  alone)  are  stained  with  the 
substance,  which  is  also  found  in  the  lumen  of  the  tubules.  This  appears 
to  show  that  under  ordinary  circumstances  the  pigment  at  any  rate  is 
eliminated  by  the  cells  of  the  convoluted  tubules,  and  that  when  by 
diminishing  the  blood-pressure,  the  filtration  of  urine  ceases,  the  pigment 
remains  in  the  convoluted  tubes,  and  is  not,  as  it  is  under  ordinary  cir- 
cumstances, swept  away  from  them  by  the  flushing  of  them  which  ordi- 
narily takes  place  with  the  watery  part  of  urine  derived  from  the  glom- 
eruli. It  therefore  is  probable  that  the  cells,  if  they  excrete  the  pigment, 
excrete  urea  and  other  substances  also.  But  urea  acts  somewhat  differ- 
ently to  the  pigment,  as  when  it  is  injected  into  the  blood  of  an  animal  in 
which  the  medulla  has  been  divided  and  the  secretion  of  urine  stopped,  a 
copious  secretion  of  urine  results,  which  is  not  the  case  when  the  pigment 
is  used  instead  under  similar  conditions.  The  flow  of  urine,  independent 
of  the  general  blood-pressure,  might  be  supposed  to  be  due  to  the  action 
of  the  altered  blood  upon  some  local  vaso-motor  mechanism;  and,  indeed, 
the  local  blood-pressure  is  directly  affected  in  this  way,  but  there  is  reason 
Vol.  I.— 24. 


370 


HAND-BOOK  OF  PHYSIOLOGY. 


for  believing  that  part  of  the  increase  of  the  secretion  is  due  to  the  direct 
stimulation  of  the  cells  by  the  urea  contained  in  the  blood. 

To  sum  up,  then,  the  relation  of  the  two  functions:  (1.)  The  process 
of  filtration,  by  which  the  chief  part  if  not  the  whole  of  the  fluid  is  elim- 
inated, together  with  certain  inorganic  salts,  and  possibly  other  solids,  is 
directly  dependent  upon  blood-pressure,  is  accomplished  by  the  renal 
glomeruli,  and  is  accompanied  by  a  free  discharge  of  solids  from  the 
tubules.  (2.)  The  process  of  secretion  proper,  by  which  urea  and  the 
principal  urinary  solids  are  eliminated,  is  only  indirectly,  if  at  all,  de- 
pendent upon  blood-pressure,  and  is  accomplished  by  the  cells  of  the  con- 
voluted tubes.  It  is  sometimes  accompanied  by  the  elimination  of  copious 
fluid,  produced  by  the  chemical  stimulation  of  the  epithelium  of  the  same 
tubules. 

Sources  of  the  Niteogenous  Urii^ary  Solids. 

Urea. — In  speaking  of  the  method  of  the  secretion  of  urine,  it  was 
assumed  that  the  part  played  by  the  cells  of  the  uriniferous  tubules  was 
that  of  mere  separation  of  the  constituents  of  the  urine  which  existed 
ready-formed  in  the  blood:  there  is  considerable  evidence  to  favor  this 
assumption.  What  may  be  called  the  specially  characteristic  solid  of  the 
urine,  i.e.,  urea  (as  well  as  most  of  the  other  solids),  may  be  detected  in 
the  blood,  and  in  other  parts  of  the  body,  e.g.,  the  humors  of  the  eye  (Mil- 
Ion),  even  while  the  functions  of  the  kidneys  are  unimpaired;  but  when 
from  any  cause,  especially  extensive  disease  or  extirpation  of  the  kidneys, 
the  separation  of  urine  is  imperfect,  the  urea  is  found  largely  in  the  blood 
and  in  most  other  fluids  of  the  body. 

It  must,  therefore,  be  clear  that  the  urea  is  for  the  most  part  made 
somewhere  else  than  in  the  kidneys,  and  simply  brought  to  them  by  the 
blood  for  elimination.  It  is  not  absolutely  proved,  however,  that  all  the 
urea  is  formed  away  from  these  organs,  and  it  is  possible  that  a  small 
quantity  is  actually  secreted  by  the  cells  of  the  tubules.  The  sources  of 
the  urea,  which  is  brought  to  the  kidneys  for  excretion,  are  stated  to  be 
two. 

(1.)  From  the  splitting  up  of  tJie  Elements  of  the  Kitrogenons  Food. — 
The  origin  of  urea  from  this  source  is  shown  by  the  increase  which  ensues 
on  substituting  an  animal  or  highly  nitrogenous  for  a  vegetable  diet;  in 
the  much  larger  amount — nearly  double — ^^excreted  by  Carnivora  than 
Ilerbivora,  independent  of  exercise;  and  in  its  diminution  to  about  one- 
half  during  starvation,  or  during  the  exclusion  of  non-nitrogenous  prin- 
ciples of  food.  Part,  at  any  rate,  of  tlie  increased  amount  of  urea  wliich 
appears  in  the  urine  soon  after  a.  full  meal  of  proteid  material  may  be 
attributed  to  the  jiroduction  of  a  considerable  amount  of  leucin  and  ty- 
rosin  as  by-products  of  pancreatic  digestion,    '^riiese  substances  are  car- 


THE  KIDNEYS  AND  URINE. 


371 


ried  by  the  portal  vein  to  the  liver,  and  it  is  there  that  the  change  in  all 
probability  takes  place;  as  when  the  functions  of  the  organ  are  gravely 
interfered  with,  as  in  the  case  of  acute  yellow  atrophy,  the  amount  of  urea 
is  distinctly  diminished,  and  its  place  appears  to  be  taken  by  leucin  and 
tyrosin.  It  has  been  found  by  experiment,  too,  that  if  these  substances 
be  introduced  into  the  alimentary  canal,  the  introduction  is  followed  by 
a  corresponding  increase  in  the  amount  of  urea,  but  not  by  the  presence 
of  the  bodies  themselves  in  the  urine. 

(2.)  From  the  JVitrogenous  metabolism  of  the  Tissues. — This  second  ori- 
gin of  urea  is  shown  by  the  fact  that  it  continues  to  be  excreted,  though  in 
smaller  quantity  than  usual,  when  all  nitrogenous  substances  are  strictly 
excluded  from  the  food,  as  when  the  diet  consists  for  several  days  of 
sugar,  starch,  gum,  oil,  and  similar  non-nitrogenous  substances  (Lehmann). 
It  is  excreted  also,  even  though  no  food  at  all  be  taken  for  a  considerable 
time;  thus  it  is  found  in  the  urine  of  reptiles  which  have  fasted  for 
months;  and  in  the  urine  of  a  madman  who  had  fasted  eighteen  days, 
Lassaigne  found  both  urea  and  all  the  components  of  healthy  urine. 

Turning  to  the  muscles,  however,  as  the  most  actively  metabolic 
tissue,  we  find  as  a  result  of  their  activity  not  urea,  but  hreatin;  and 
although  it  may  be  supposed  that  some  of  this  latter  body  appears  natur- 
ally as  hreatinin,  yet  it  is  not  in  sufficient  quantity  to  represent  the  large 
amount  of  it  formed  by  the  muscles,  and,  indeed,  by  others  of  the  tissues. 
It  is  assumed  that  kreatin  therefore  is  the  nitrogenous  antecedent  of  urea; 
where  its  conversion  into  urea  takes  place  is  doubtful,  but  very  likely  the 
liver,  and  possibly  the  spleen,  may  be  the  seats  of  the  change.  It  may  be, 
however,  that  part — but  if  so,  a  small  part — reaches  the  kidneys  without 
previous  change,  leaving  it  to  the  cells  of  the  renal  tubules  to  complete  the 
action.  In  speaking  of  kreatin  as  the  antecedent  of  urea,  it  should  be 
recollected  that  other  nitrogenous  products,  such  as  xanthin  (C^H^N^OJ, 
appear  in  conjunction  with  it,  and  that  these  may  also  be  converted  into 
urea. 

It  was  formerly  taken  for  granted  that  the  quantity  of  urea  in  the 
urine  is  greatly  increased  by  active  exercise;  but  numerous  observers  have 
failed  to  detect  more  than  a  slight  increase  under  such  circumstances;  and 
our  notions  concerning  the  relation  of  this  excretory  product  to  the  de- 
struction of  muscular  fibre,  consequent  on  the  exercise  of  the  latter,  have 
undergone  considerable  modification.  There  is  no  doubt,  of  course,  that 
like  all  parts  of  the  body,  the  muscles  have  but  a  limited  term  of  exist- 
ence, and  are  being  constantly  although  very  slowly  renewed,  at  the  same 
time  that  a  part  of  the  products  of  their  disintegration  appears  in  the 
urine  in  the  form  of  urea.  But  the  waste  is  not  so  fast  as  it  was  formerly 
supposed  to  be;  and  the  theory  that  the  amount  of  work  done  by  the 
muscle  is  expressed  by  the  quantity  of  urea  excreted  in  the  urine  must 
without  doubt  be  given  up. 


372 


HAT^D-BOOK  OF  PHYSIOLOGY. 


Uric  Acid. — Uric  acid  probably  arises  much  in  the  same  way  as  urea, 
either  from  the  disintegration  of  albuminous  tissues,  or  from  the  food. 
The  relation  which  uric  acid  and  urea  bear  to  each  other  is,  however,  still 
obscure:  but  uric  acid  is  said  to  be  a  less  advanced  stage  of  the  oxidation 
of  the  products  of  proteid  metabolism.  The  fact  that  they  often  exist 
together  in  the  same  urine,  makes  it  seem  probable  that  they  have  differ- 
ent origins;  but  the  entire  replacement  of  either  by  the  other,  as  of  urea 
by  uric  acid  in  the  urine  of  birds,  serpents,  and  many  insects,  and  of  uric 
acid  by  urea,  in  the  urine  of  the  feline  tribe  of  Mammalia,  shows  that 
either  alone  may  take  the  place  of  the  two.  At  any  rate,  although  it  is 
true  that  one  molecule  of  uric  acid  is  capable  of  splitting  up  into  two 
molecules  of  urea  and  one  of  mes-oxalic  acid,  there  is  no  evidence  for 
believing  that  uric  acid  is  an  antecedent  of  urea  in  the  nitrogenous 
metabolism  of  the  body.  Some  experiments  seem  to  show  that  uric  acid 
is  formed  in  the  kidney. 

Hippuric  Acid  (CgHgXOg). — Hippuric  acid  is  closely  allied  to  benzoic 
acid;  and  this  substance  when  introduced  into  the  system,  is  excreted  by 
the  kidneys  as  hippuric  acid  (Urel.  Its  source  is  not  satisfactorily  deter- 
mined: in  part  it  is  probably  derived  from  some  constituents  of  vegetable 
diet,  though  man  has  no  hippuric  acid  in  his  food,  nor,  commonly,  any 
benzoic  acid  that  might  be  converted  into  it;  in  part  from  the  natural 
disintegration  of  tissues,  independent  of  vegetable  food,  for  AVeismann 
constantly  found  an  appreciable  quantity,  even  when  living  on  an  exclu- 
sively animal  diet.  Hippuric  acid  arises  from  the  union  of  benzoic  acid 
with  glycin  (C,H,NO,  +  C,llfi„  =  C.R.'KO,  +  H,0),  which  union  may 
take  place  in  the  kidneys  themselves,  as  well  as  in  the  liver. 

Hxtractives. — The  source  of  the  extractives  of  the  urine  is  probably 
in  chief  part  the  disintegration  of  the  nitrogenous  tissues,  but  we  are 
unable  to  say  whether  these  nitrogenous  bodies  are  merely  accidental, 
having  resisted  further  decomposition  into  urea,  or  whether  they  are  the 
representatives  of  the  decomposition  of  special  tissues,  or  of  special  forms 
of  metabolism  of  the  tissues.  There  is,  however,  one  excejition.  and  this 
is  in  the  case  of  kreatinin;  there  is  great  reason  for  believing  that  the 
amount  of  this  body  which  appears  in  the  urine  is  derived  from  the  metab- 
olism of  the  nitrogenous  food,  as  when  this  is  diminished,  it  diminishes* 
and  when  stopped,  it  no  longer  appears  in  the  urine. 

The  Passage  of  Urixe  ixto  the  Bladder. 

As  cacli  portion  of  urine  is  secreted  it  propels  that  wliich  is  already 
in  the  tubes  onward  into  the  pelvis  of  the  kidney.  Thence  through  the 
ureter  the  urine  passes  into  the  bladder,  into  which  its  rate  and  mode  of 
entrance  lias  been  watched  in  cases  of  ectopia  review,  i.e.,  of  such  fissures 
in  the  anteriyr  or  lower  ]nirt  of  the  walls  of  the  abdomen,  and  of  the  front 


THE  KIDNEYS  AND  URINE. 


373 


wall  of  the  bladder,  as  expose  to  view  its  hinder  wall  together  with  the 
orifices  of  the  ureters.  The  urine  does  not  enter  the  bladder  at  any  reg- 
ular rate,  nor  is  there  a  synchronism  in  its  movement  through  the  two 
ureters.  During  fasting,  two  or  three  drops  enter  the  bladder  every 
minute,  each  drop  as  it  enters  first  raising  up  the  little  papilla  on  which, 
in  these  cases,  the  ureter  opens,  and  then  passing  slowly  through  its  orifice, 
which  at  once  again  closes  like  a  sphincter.  In  the  recumbent  posture, 
the  urine  collects  for  a  little  time  in  the  ureters,  then  flows  gently,  and, 
if  the  body  be  raised,  runs  from  them  in  a  stream  till  they  are  empty. 
Its  flow  is  increased  in  deep  inspiration,  or  straining,  and  in  active  exer- 
cise, and  in  fifteen  or  twenty  minutes  after  a  meal  (Erichsen).  The 
urine  collecting  is  prevented  from  regurgitation  into  the  ureters  by  the 
mode  in  which  these  pass  through'  the  walls  of  the  bladder,  namely,  by 
their  lying  for  between  half  and  three-quarters  of  an  inch  between  the 
muscular  and  mucous  coats  before  they  turn  rather  abruptly  forward, 
and  open  through  the  latter  into  the  interior  of  the  bladder. 

Micturition. — The  contraction  of  the  muscular  walls  of  the  bladder 
may  by  itself  expel  the  urine  with  little  or  no  help  from  other  muscles, 
when  the  sphincter  of  the  organ  is  relaxed.  In  so  far,  however,  as  it  is  a 
voliuitai^y  act,  micturition  is  performed  by  means  of  the  abdominal  and 
other  expiratory  muscles  which,  in  their  contraction,  press  on  the  abdom- 
inal viscera,  the  diaphragm  being  fixed,  and  cause  the  expulsion  of  the 
contents  of  the  bladder.  The  muscular  coat  of  the  bladder  co-operates, 
in  micturition,  by  reflex  involuntary  action,  with  the  abdominal  muscles; 
and  the  act  is  completed  by  the  accelerator  urines,  which,  as  its  name 
implies,  quickens  the  stream,  and  expels  the  last  drops  of  urine  from  the 
urethra.  The  act,  so  far  as  it  is  not  directed  by  volition,  is  under  the 
control  of  a  nervous  centre  in  the  lumbar  spinal  cord,  through  which,  as 
in  the  case  of  the  similar  centre  for  defgecation  (p.  288),  the  various 
muscles  concerned  are  harmonized  in  their  action.  It  is  well  known  that 
the  act  may  be  reflexly  induced,  e.g.,  in  children  who  suffer  from  intes- 
tinal worms,  or  other  such  irritation.  Generally  the  afferent  impulse 
which  calls  into  action  the  desire  to  micturate  is  excited  by  over  disten- 
tion of  the  bladder,  or  even  by  a  few  drops  of  urine  passing  into  the 
urethra. 


END  OF  YOL.  I. 


KIEKES'  IIAISTD-BOOK  OF  PHYSIOLOGY 


HAI^D-BOOK 

OF 

PHYSIOLOGY 

BY 

W.  MOEEANT  BAKEE,  F.E.O.S. 

SURGEON  TO  ST.   BARTHOLOMEW'S  HOSPITAL  AND   CONSULTING  SURGEON  TO  THE  EVELINA  HOSPITAL 
FOE    SICK    children:    lecturer    on    PHYSIOLOGY    AT    ST.    BARTHOLOMEW'S  HOSPITAL. 
AND  LATE  MEMBER  OP  THE    BOARD  OP  EXAMINERS    OP  THE    ROYAL  COLLEGE 
OP  SURGEONS  OP  ENGLAND. 

AND 

VINCENT  DORMEE  HARRIS,  M.D.,  Lond. 

DEMONSTRATOR  OP  PHYSIOLOGY  AT  ST.  BARTHOLOMEW'S  HOSPITAL. 

ELEVENTH  EDITION 

WITH  NEARLY  BOO  ILLUSTRATIONS 

TWO  VOLUMES  IN  ONE 
VOLUME  II 


NEW  YOEK 

WILLIAM  WOOD  &  COMPANY 

56  &  58  Lafayette  Place 
1886 


OOITTENTS  TO  VOLUME  II. 


CHAPTER  XIV. 

PAGE 

The  Vascular  Glands   1 

Structure  and  Functions  of  the  Spleen   3 

Thymus   5 

Thyroid   7 

"        "         "         Supra-renal  capsules   8 

Pituitary  Body   10 

Pineal  Gland   .10 

Functions  of  the  Vascular  Glands  in  general   10 

CHAPTER  XV. 

Causes  and  Phenomena  op  Motion   12 

Ciliary  Motion   12 

Amoeboid  Motion   13 

Muscular  Motion  ■   14 

Plain  or  Unstriped  Muscle  .14 

Striated  Muscle   15 

Development  of  Muscle   20 

Physiology  of  Muscle  at  rest  .20 

"              "in  activity   24 

Kigor  Mortis   37 

Actions  of  the  Voluntary  Muscles  .39 

"         "    Involuntary  Muscles   44 

Sources  of  Muscular  Action   44 

Electrical  Currents  in  Nerves   45 

CHAPTER  XVL 

The  Voice  and  Speech   50 

Mode  of  Production  of  the  Human  Voice   50 

The  Larynx   51 

Application  of  the  Voice^n  Singing  and  Speaking   56 

Speech   60 


iv 


CONTENTS. 


CHAPTER  XVII. 

PAGE 

Nutkition:  The  Income  and  Expenditure  op  the  Human  Body    .      .  63 
Nitrogenous  Equilibrium  and  Formation  of  Fat  66 


CHAPTER  XVIII. 

The  Nervous  System      .                                                        .      .  6{ 

Elementary  Structures  of  the  Nervous  System    ......  6^ 

Structure  of  Nerve-Fibres     .                                                     .      .  Q{ 

Terminations  of  Nerve-Fibres      .      .   7^ 

Structure  of  Nerve-Centres   7"; 

Functions  of  Nerve-Fibres   7{ 

Classification  of  Nerve-Fibres   8( 

Laws  of  Conduction  in  Nerve- Fibres                                                .  8j 

Functions  of  Nerve-Centres  ........      I      ,.  8( 

Laws  of  Reflex  Actions   8{ 

Secondary  or  Acquired  Reflex  Actions   8' 


Cerebro- SPINAL  Nervous  System 

The  Spinal  Cord  and  its  Nerves   90 

The  White  Matter  of  the  Spinal  Cord   91 

The  Grey  Matter  of  the  Spinal  Cord   .  .92 

Nerves  of  the  Spinal  Cord   94 

Functions  of  the  Spinal  Cord       .    97 

^HE  Medulla  Oblongata   105 

Its  Structure   105 

Distribution  of  the  Fibres  of  the  Medulla  Oblongata   106 

Functions  Of  the  Medulla  Oblongata   109 


Structure  and  Physiology  of  the  Pons  Varolii,  Crura  Cerebri,  Cor- 
pora Quadrigemina,  Corpora  Geniculata,  Optic  Thalami,  and  Cor- 


pora Striata    112 

Pons  Varolii         .      .       .  .112 

Crura  Cerebri        .   113 

Corpora  Quadrigemina   114 

Corpora  Striata  and  Optic  Thalami   114 

The  Cerebellum   115 

Functions  of  the  Cerebellum   118 


The  Cerebrum   120 

Convolutions  of  the  Cerebrum      .       .   120 

Structure  of  the  Cerebrum   123 

€hemical  Composition  of  the  Grey  and  White  Matter   125 

Functions  of  the  Cerebrum  ,       .       .       .  127 

Effects  of  the  Removal  of  the  Cerebrum   128 

Localization  of  Functions   129 

Experimental  Localization  of  Functions      .      .  •   131 

Sleep   135 


CONTENTS. 


Physiology  of  the  Cranial  Nerves     .      .      ,      .  ,     .      .      •      .  136 


Phys: 


ology  of  the  Third  Cranial  Nerve  137 

Fourth  Cranial  Nerve   .138 

Fifth  or  Trigeminal  Nerve  139 

Sixth  Nerve  143 

Facial  Nerve    .       .  144 

Glosso-Pharyhgeal  Nerve  145 

Pneumogastric  Nerve  146 

Spinal  Accessory  Nerve  .      .      .      .      .      .  .149 

Hypoglossal  Nerve  .      .      .      .      .      •      .      .  150 


Physiology  of  the  Spinal  Nerves  . 


150 


Physiology  of  the  Sympathetic  Nerve  151 

Functions  of  the  Sympathetic  Nervous  System  153 


CHAPTER  XIX. 


The  Senses  -      .      .  158 

Common  Sensations  .       .       .       ,  158 

Special  Sensations     ...........  159 

The  Sense  of  Touch  .      .  ........  163 

The  Sense  of  Taste   168 

The  Tongue  and  its  Papillae   .  .169 

The  Sense  of  Smell   175 

The  Sense  of  Hearing     .      .      .     ^   .179 

Anatomy  of  the  Organ  of  Hearing    ....      .      .      .       .  .  179 

Physiology  of  Hearing  186 

Functions  of  the  External  Ear                                                 .  .  186 

Functions  of  the  Middle  Ear;  the  Tympanum,  Ossicula,  and  Fenestras  .  187 

Functions  of  the  Labyrinth                                               .       .  .  191 

Sensibility  of  the  Auditory  Nerve     .      .      .      .    '  .      .      .  .193 

The  Sense  of  Sight   .      ...      .  .196 

The  Eyelids  and  Lachrymal  Apparatus    .      ...      .       .       .  196 

The  Structure  of  the  Eyeball  197 

Optical  Apparatus  '  203 

Accommodation  of  the  Eye      .       .  206 

Defects  in  the  Apparatus  ,      .      .  .211 

Spherical  Aberration  .       .       ,  212 

Chromatic  Aberration       .       .       .       .       .      .      .      .       .      .  213 

The  Blind  Spot  .       ...      .      .      .      .      .      .      .  .215 

Visual  Purple  21^ 

Color  Sensations   .      .      .      .      .  233 


vi 


CONTENTS. 


PAGE 

Eeciprocal  Action  of  different  parts  of  the  Retina   226 

Movements  of  the  Eye   228 

Simultaneous  Action  of  the  two  Eyes   228 

CHAPTER  XX. 

Generation  and  Development       .      .      .      ,      .      ,      ,  .234 

Generative  Organs  of  the  Female   234 

Unimpregnated  Ovum   236 

Discharge  of  the  Ovum   239 

Menstruation   240 

Corpus  Luteum  ,      .      ,             ...  243 

Impregnation  op  the  Ovum   246 

Male  Sexual  Functions   246 

Structure  of  the  Testicle    .  "   246 

Spermatozoa   247 

The  Semen  .   251 

Development   252 

Changes  of  the  Ovum  up  to  the  Formation  of  the  Blastoderm .      .      .  252 

Segmentation  of  the  Ovum   253 

Fundamental  Layers  of  the  Blastoderm:  Epiblast;  Mesoblast;  Hypoblast.  255 

First  Rudiments  of  the  Embryo  and  its  Chief  Organs      ....  256 

Foetal  Membranes   261 

The  Umbilical  Vesicle                                                            .       .  262 

The  Amnion  and  AUantois   262 

The  Chorion   264 

Changes  of  the  Mucous  Membrane  of  the  Uterus  and  Formation  of  the 

.  Placenta   266 

Development  of  Organs   270 

Development  of  the  Vertebral  Column  and  Cranium      ....  270 

"            "    Face  and  Visceral  Arches   273 

"    Extremities   275 

"    Vascular  System   276 

Circulation  of  Blood  in  the  Foetus   286 

Development  of  the  Nervous  System   287 

'*    Organs  of  Sense   291 

'*            "    Alimentary  Canal   295 

**            "     Respiratory  Apparatus   298 

'*  "    Wolffian  Bodies,  Urinary  Apparatus,  and  Sexual 

Organs   298 

CHAPTER  XXI. 

On  the  Relation  of  Life  to  other  Forces   806 


CONTENTS.  vii 

APPENDIX  A: 

PAGE 

The  Chemical  Basis  of  the  Human  Body   335 

APPENDIX  B  : 

Anatomical  Weights  and  Measures   345 

Measures  of  Weight   345 

"  Length   345 

Sizes  of  various  Histological  Elements  and  Tissues   346 

Specific  Gravity  of  various  Fluids  and  Tissues   347 

Table  showing  the  percentage  composition  of  various  Articles  of  Food  .  347 

Classification  of  the  Animal  Kingdom   348 

"   349 


INDEX  351 


HAID-BOOK  OF  PHYSIOLOGY. 


CHAPTER  XIV. 

THE  VASCULAR  GLANDS. 

The  materials  separated  from  the  blood  by  the  ordinary  process  of 
secretion  in  glands,  are  always  discharged  from  the  organ  in  which  they 
are  formed,  and  are  either  straightway  expelled  from  the  body,  or  if  they 
are  again  received  into  the  blood,  it  is  only  after  they  have  been  altered 
from  their  original  condition,  as  in  the  cases  of  the  saliva  and  bile.  There 
appears,  however,  to  be  a  modification  of  the  process  of  secretion,  in  which 
certain  materials  are  abstracted  from  the  blood,  undergo  some  change, 
and  are  added  to  the  lymph  or  restored  to  the  blood,  without  being  pre- 
viously discharged  from  the  secreting  organ,  or  made  use  of  for  any  second- 
ary purpose.  The  bodies  in  which  this  modified  form  of  secretion  takes 
place,  are  usually  described  as  vascular  glands,  or  glands  without  ducts,  and 
include  the  spleen,  the  thymus  and  thyroid  glands,  the  supra-renal  cap- 
sules, the  pineal  gland  audi  pituitary  body,  the  tonsils.  The  solitary  and 
agminate  glands  (Peyer^s)  of  the  intestine,  and  lymph-glands  in  general, 
also  closely  resemble  them;  indeed,  both  in  structure  and  function,  the 
vascular  glands  bear  a  close  relation,  on  the  one  hand,  to  the  true  secret- 
ing glands,  and  on  the  other,  to  the  lymphatic  glands.  The  evidence  in 
favor  of  the  view  that  these  organs  exercise  a  function  analogous  to  that  of 
secreting  glands,  has  been  chiefly  obtained  from  investigations  into  their 
structure,  which  have  shown  that  most  of  the  glands  without  ducts  contain 
the  same  essential  structures  as  the  secreting  glands,  except  the  ducts. 

The  Spleen. 

The  Spleen  is  the  largest  of  the  so-called  ductless  glands;  it  is  situated' 
to  the  left  of  the  stomach,  between  it  and  the  diaphragm.   It  is  of  a  deep 
red  color,  of  a  variable  shape,  generally  oval,  somewhat  concavo-convex. 
Vessels  enter  and  leave  the  spleen  at  the  inner  side  (hilus). 
Vol.  IL— 1. 


2 


HAND-BOOK  OF  PHYSIOLOGY. 


Structure. — The  spleen  is  covered  externally  almost  completely  by 
a  serous  coat  derived  from  the  peritoneum,  while  Avithin  this  is  the  proper 
fibrous  coat  or  capsule  of  the  organ.  The  latter,  composed  of  connective 
tissue,  with  a  large  preponderance  of  elastic  fibres,  and  a  certain  propor- 
tion of  unstriated  muscular  tissue,  forms  the  immediate  investment  of  the 
spleen.  Prolonged  from  its  inner  surface  are  fibrous  processes  or  trabeculcB, 
containing  much  unstriated  muscle,  which  enter  the  interior  of  the  organ, 
and,  dividing  and  anastomosing  in  all  parts,  form  a  kind  of  supporting 


Fig.  254.— Section  of  dog's  spleen  injected:  c,  capsule;  fr,  trabeculae;  m,  two  Malpighian  bcxiies 
with  numerous  small  arteries  and  capillaries;  a,  artery;  Z,  lymphoid  tissue,  consisting  of  closely- 
packed  lymphoid  cells  supported  by  very  delicate  retiform  tissue ;  a  light  space  unoccupied  by  cells  is 
seen  all  round  the  trabecute,  wliich"  corresponds  to  the  "  lymph  path"'  Ij-mphatic  glands.  (.Schofield.) 

framework  or  .stroma,  in  the  interstices  of  which  the  proper  substance  of 
the  spleen  {splee?i-pulp)  is  contained  (Fig.  254).  At  the  hilus  of  the 
spleen,  the  blood-vessels,  nerves,  and  lymphatics  enter,  and  the  fibrous 
coat  is  prolonged  into  the  spleen-substance  in  the  form  of  investing  sheaths 
for  the  arteries  and  veins,  which  sheaths  again  are  continuous  with  the 
trahpculm  before  referred  to. 

The  splcen-pnlp,  wliich  is  a  dark  red  or  reddish-brown  color,  is  com- 
posed chiefly  of  cells,  imbedded  in  a  matrix  of  libres  formed  of  the 
branching  of  large  flattened  nucleated  endotheloid  cells.  The  spaces  of 
the  network  only  partially  occupied  by  colls  form  fi  freely  communicating 


THE  VASCULAR  GLANDS. 


3 


system.  Of  the  cells  some  are  granular  corpuscles  resembling  the  lymph 
corpuscles,  more  or  less  connected  with  the  cells  of  the  meshwork,  both 
in  general  appearance  and  in  being  able  to  perform  amoeboid  movements; 
others  are  red  blood-corpuscles  of  normal  appearance  or  variously  changed; 
while  there  are  also  large  cells  containing  either  a  pigment  allied  to  the 
coloring  matter  of  the  blood,  or  rounded  corpuscles  like  red  blood-cells. 

The  splenic  artery,  after  entering  the  spleen  by  its  concave  surface, 
divides  and  subdivides,  with  but  little  anastomosis  between  its  branches; 
at  the  same  time  its  branches  are  sheathed  by  the  prolongations  of  fibrous 
coat,  which  they,  so  to  speak,  carry  into  the  spleen  with  them.  The 
arteries  send  off  branches  into  the  spleen-pulp  which  end  in  capillaries, 
and  these  either  communicate,  as  in  other  parts  of  the  body,  with  t*he 
radicles  of  the  veins,  or  end  in  lacunar  spaces  in  the  spleen-pulp,  from 
which  veins  arise  (Gray). 

The  walls  of  the  smaller  veins  are  more  or  less  incomplete,  and  readily 
allow  lymphoid  corpuscles  to  be  swept  into  the  blood-current.  ''The 
blood  traverses  the  network  of  the  pulp,  and  interstices  of  the  lymphoid 
cells  contained  in  the  latter,  in  the  same  manner  as  the  water  of  a  river 
finds  its  way  among  the  pebbles  of  its  bed:  the  blood  from  the  arterial 
capillaries  is  emptied  into  a  system  of  intermediate  passages,  which  are 
directly  bounded  by  the  cells  and  fibres  of  the  network  of  the  pulp,  and 
from  which  the  smallest  venous  radicles  with  their  cribriform  walls  take 
origin^'  (Prey).  The  veins  are  large  and  very  distensible:  the  whole  tis- 
sue of  the  spleen  is  highly  vascular,  and  becomes  readily  engorged  with 
blood:  the  amouni;  of  distension  is,  however,  limited  by  the  fibrous  and 
muscular  tissue  of  its  capsule  and  trabeculge,  which  forms  an  investment 
and  support  for  the  pulpy  mass  within. 

On  the  face  of  a  section  of  the  spleen  can  be  usually  seen  readily  with 
the  naked  eye,  minute,  scattered  rounded  or  oval  whitish  spots,  mostly 
from  -3V  to  gig-  inch  in  diameter.  These  are  the  MalpigUian  corpuscles 
of  the  spleen,  and  are  situated  on  the  sheaths  of  the  minute  splenic  arte- 
ries, of  which,  indeed,  they  may  be  said  to  be  outgrowths  (Fig.  254).  For 
while  the  sheaths  of  the  larger  arteries  are  constructed  of  ordinary  con- 
nective tissue,  this  has  become  modified  where  it  forms  an  investment 
for  the  smaller  vessels,  so  as  to  be  composed  of  adenoid  tissue,  with  abun- 
dance of  corpuscles,  like  lymph-corpuscles,  contained  in  its  meshes,  and 
the  Malpighian  corpuscles  are  but  small  outgrowths  of  this  cytogenous  or 
cell-bearing  connective  tissue.  They  are  composed  of  cylindrical  masses  of 
corpuscles,  intersected  in  all  parts  by  a  delicate  fibrillar  tissue,  which 
though  it  invests  the  Malpighian  bodies,  does  not  form  a  complete  cap- 
sule. Blood-capillaries  traverse  the  Malpighian  corpuscles  and  form  a 
plexus  in  their  interior.  The  structure  of  a  Malpighian  corpuscle  of  the 
spleen  is,  therefore,  very  similar  to  that  of  lymphatic-gland  substance. 

Functions. — With  respect  to  the  office  of  the  spleen,  we  have  the 


4 


HAND-BOOK  OF  PHYSIOLOGY. 


following  data.  (1.)  The  large  size  which  it  gradually  acquires  toward 
the  termination  of  the  digestive  process,  and  the  great  increase  observed 
about  this  period  in  the  amount  of  the  finely-granular  albuminous  plasma 
within  its  parenchyma,  and  the  subsequent  gradual  decrease  of  this  mate- 
rial, seem  to  indicate  that  this  organ  is  concerned  in  elaborating  the  albu- 
minous materials  of  food,  and  for  a  time  storing  them  up,  to  be  gradually 
introduced  into  the  blood,  according  to  the  demands  of  the  general 
system. 

(2.)  It  seems  probable  that  the  spleen,  like  the  lymphatic  glands,  is 
engaged  in  the  formation  of  blood-corpuscles.  For  it  is  quite  certain, 
that  the  blood  of  the  splenic  vein  contains  an  unusually  large  amount  of 
white  corpuscles;  and  in  the  disease  termed  leucocythaemia,  in  which  the 
pale  corpuscles  of  the  blood  are  remarkably  increased  in  number,  there  is 
almost  always  found  an  hyper tropliied  state  of  the  spleen  or  of  the  lym- 
phatic glands.  In  Kolliker's  opinion,  the  development  of  colorless  and 
also  colored  corpuscles  of  the  blood  is  one  of  the  essential  functions  of 
the  spleen,  into  the  veins  of  which  the  new-formed  corpuscles  pass,  and 
are  thus  conveyed  into  the  general  current  of  the  circulation. 

(3.)  There  is  reason  to  believe,  that  in  the  spleen  many  of  the  red  cor- 
puscles of  the  blood,  those  probably  which  have  discharged  their  office 
and  are  worn  out,  undergo  disintegration;  for  in  the  colored  portions  of 
the  spleen-pulp  an  abundance  of  such  corpuscles,  in  various  stages  of 
degeneration,  are  found,  while  the  red  corpuscles  in  the  splenic  venous 
blood  are  said  to  be  relatively  diminished.  This  process  appears  to  be  as 
follows.  The  blood-corpuscles,  becoming  smaller  and  darker,  collect  to- 
gether in  roundish  heaps,  which  may  remain  in  this  condition,  or  become 
each  surrounded  by  a  cell-wall.  The  cells  thus  produced  may  contain 
from  one  to  twenty  blood-corpuscles  in  their  interior.  These  corpuscles 
become  smaller  and  smaller;  exchange  their  red  for  a  golden  yellow, 
brown,  or  black  color;  and  at  length,  are  converted  into  pigment- 
granules,  which  by  degrees  become  paler  and  paler,  until  all  color  is  lost. 
The  corpuscles  undergo  these  changes  whether  the  heaps  of  them  are 
enveloped  by  a  cell-wall  or  not. 

(4. )  From  the  almost  constant  presence  of  uric  acid,  as  well  as  of  the 
nitrogenous  bodies,  xanthin,  hypoxanthin,  and  leucin,  in  the  spleen, 
some  nitrogenous  metabolism  may  be  fairly  inferred  to  occur  in  it. 

(5.)  Besides  these,  its  supposed  direct  offices,  the  spleen  is  believed  to 
fulfil  some  purpose  in  regard  to  the  portal  circulation,  with  which  it  is  in 
close  connection.  From  the  readiness  with  which  it  admits  of  being  dis- 
tended, and  from  the  fact  that  it  is  generally  small  while  gastric  diges- 
tion is  going  on,  and  enlarges  when  that  act  is  concluded,  it  is  supposed 
to  act  as  a  kind  of  vascular  reservoir,  or  diverticulum  to  the  portal  S3'stem, 
or  more  particularly  to  the  vessels  of  the  stomach.  That  it  may  serve 
such  a  purpose  is  also  made  probable  by  the  enlargement  which  it  under- 


THE  VASCULAR  GLANDS. 


5 


goes  in  certain  affections  of  the  heart  and  liver,  attended  with  obstruction 
to  the  passage  of  blood  through  the  latter  organ,  and  by  its  diminution 
when  the  congestion  of  the  portal  system  is  relieved  by  discharges  from 
the  bowels,  or  by  the  effusion  of  blood  into  the  stomach.  This  mechani- 
cal influence  on  the  circulation,  however,  can  hardly  be  supposed  to  be 
more  than  a  very  subordinate  function. 

It  is  only  necessary  to  mention  that  Schiff  believes  that  the  spleen 
manufactures  a  substance  without  which  the  pancreatic  secretion  cannot 
act  upon  proteids,  so  that  when  the  spleen  is  removed  the  digestive  action 
of  the  pancreas  is  stopped. 

Influence  of  the  Nervous  System  upon  the  Spleen. — When  the 
spleen  is  enlarged  after  digestion,  its  enlargement  is  probably  due  to  two 
causes,  (1)  a  relaxation  of  the  muscular  tissue  which  forms  so  large  a 
part  of  its  framework;  (2)  a  dilatation  of  the  vessels.  Both  these  phe- 
nomena are  doubtless  under  control  of  the  nervous  system.  It  has  been 
found  by  experiment  that  when  the  splenic  nerves  are  cut  the  spleen 
enlarges,  and  that  contraction  can  be  brought  about  (1)  by  stimulation 
of  the  spinal  cord  (or  of  the  divided  nerves) ; 
(2)  reflexly  by  stimulation  of  the  central 
stumps  of  certain  divided  nerves,  e.g.,  vagus 
and  sciatic;  (3)  by  local  stimulation  by  an 
electric  current;  (4)  the  exhibition  of  quinine 
and  some  other  drugs.  It  has  been  shown  by 
means  of  a  modification  of  the  plethysmo- 
graph  (Roy),  that  the  spleen  undergoes  rhyth- 
mical contractions  and  dilatations,  due  no 
doubt  to  the  contraction  and  relaxation  of 
the  muscular  tissue  in  its  capsule  and  tra- 
beculae.  The  gland  also  shows  the  rhythmical 
alteration  of  the  general  blood  pressure,  but 
to  a  less  extent  than  the  kidney. 

The  Thymus. 

This  gland  must  be  looked  upon  as  a  tem- 
porary organ,  as  it  attains  its  greatest  size 
early  after  birth,  and  after  the  second  year 
gradually  diminishes,  until  in  adult  life  hard- 
ly a  vestige  remains.  At  its  greatest  devel- 
opment it  is  a  long  narrow  body,  situated  in  the  front  of  the  chest  behind 
the  sternum  and  partly  in  the  lower  part  of  the  neck.  It  is  of  a  reddish 
or  greyish  color,  distinctly  lobulated. 

Structure. — The  gland  is  surrounded  by  a  fibrous  capsule  which 


Fig.  255.— Transverse  section  of  a 
lobule  of  an  injected  infantile  thymus 
gland,  a,  capsule  of  connective  tis- 
sue surrounding  the  lobule;  6,  mem- 
brane of  the  glandular  vesicles;  c, 
cavity  of  the  lobule,  from  which  the 
larger  blood-vessels  are  seen  to  ex- 
tend toward  and  ramify  in  the  sphe- 
roidal masses  of  the  lobule.  X  30. 
(KoUiker.) 


6  HAND-BOOK  OF  PHYSIOLOGY. 

sends  in  processes,  forming  trabeculae,  which  divide  the  gland  into  lobes, 
and  carry  the  blood  and  lymph-vessels.  The  large  trabeculae  branch  into 
small  ones,  which  divide  the  lobes  into  lobules.  The  gland  is  encased  in 
a  fold  of  the  pleura.  The  lobules  are  further  subdivided  into  follicles  by 
fine  connective  tissue.  A  follicle  (Fig.  256)  is  more  or  less  polyhedral  in 
shape,  and  consists  of  cortical  and  medullary  portions,  the  structure  of 
both  being  of  adenoid  tissue,  but  in  the  medullary 
portion  the  matrix  is  coarser,  and  is  not  so  filled  up 
with  lymphoid  corpuscles  as  in  the  cortex.  The 
adenoid  tissue  of  the  cortex,  and  to  a  less  marked  ex- 
tent in  the  medulla,  consists  of  two  kinds  of  tissue, 
one  with  small  meshes  formed  of  fine  fibres  with 
thickened  nodal  points,  and  the  other  enclosed  within 
the  first,  composed  of  branched  connective-tissue  cor- 
puscles (Watney).  Scattered  in  the  adenoid  tissue  of 
the  medulla  are  the  concentric  corpuscles  of  Hassall, 
which  are  protoplasmic  masses  of  various  sizes,  con- 
sisting of  a  central  nucleated  granular  centre,  sur- 
rounded by  flattened  nucleated  endothelial  cells.  In 
the  reticulum,  especially  of  the  medulla,  are  large 
transparent  giant  cells.  In  the  thymus  of  the  dog  and  of  other  animals 
are  to  be  found  cysts,  probably  derived  from  the  concentric  corpuscles, 
some  of  which  are  lined  with  ciliated  epithelium,  and  others  with  short 
columnar  cells.  Haemoglobin  is  found  in  the  thymus  of  all  animals, 
either  in  these  cysts,  or  in  cells  near  to  or  of  the  concentric  corpuscles. 
In  the  lymph  issuing  from  the  thymus  are  found  cells  containing  colored 
blood-corpuscles  and  hemoglobin  granules,  and  in  the  lymphatics  of  the 
thymus  there  are  more  colorless  cells  than  in  the  lymphatics  of  the  neck. 
In  the  blood  of  the  thymic  vein,  there  appears  sometimes  to  be  an  in- 
crease in  the  colorless  corpuscles  and  also  masses  of  granular  matter  (cor- 
puscles of  Zimmermann)  (Watney).  The  arteries  radiate  from  the  centre 
of  the  gland.  Lymph  sinuses  may  be  seen  occasionally  surrounding  a 
greater  or  smaller  portion  of  the  periphery  of  the  follicles  (Klein).  The 
nerves  are  very  minute. 

Function. — The  thymus  appears  to  take  part  in  producing  colored 
corpuscles,  both  from  the  large  corpuscles  containing  haemoglobin,  and 
also  indirectly  from  the  colorless  corpuscles  (Watney).  Respecting  the 
function  of  the  gland  in  the  hybernating  animals,  in  Avhich  it  exists 
throughout  life;  as  each  successive  period  of  hibernation  approaches,  the 
thymus  greatly  enlarges  and  becomes  laden  with  fat,  which  accumulates 
in  it  and  in  fat-glands  connected  with  it,  in  even  larger  proportions 
than  it  does  in  the  ordinary  seats  of  adipose  tissue.  Hence  it  appears 
to  serve  for  the  storing  up  of  materials  which,  being  re-absorbed  in 
inactivity  of  the  hibernating  period,  may  maintain  the  respiration  and 


Fig.  256.— From  a  hor- 
izontal section  through 
superficial  part  of  the 
thymus  of  a  calf,  slight- 
ly magnified.  Showing 
in  the  centre  a  follicle 
of  polygonal  shape  with 
similarly  shaped  folli- 
cles round  it.  (Klein 
and  Noble  Smith.) 


THE  VASCULAK  GLANDS.  7 

the  temperature  of  the  body  in  the  reduced  state  to  which  they  fall 
during  that  time. 

The  Thyroid. 

The  Thyroid  gland  is  situated  in  the  neck.  It  consists  of  two  lobes, 
one  on  each  side  of  the  trachea  extending  upward  to  the  thyroid  cartilage, 
covering  its  inferior  cornu  and  part  of  its  body;  these  lobes  are  connected 


Fig.  257.— Part  of  a  section  of  the  hiunan  Thyroid,  a,  fibrous  capsule;  6,  thyroid  vesicles  filled 
with,  e,  colloid  substance;  c,  supporting  fibrous  tissue;  d,  short  columnar  cells  lining  vesicles;  /,  ar- 
teries; g,  veins  filled  with  blood;  h,  lymphatic  vessel  filled  with  colloid  substance.   (S.  K.  Alcock.) 

across  the  middle  line  oy  a  middle  lobe  or  isthmus.  The  thyroid  is  cov- 
ered by  the  muscles  of  the  neck.  It  is  highly  vascular,  and  varies  in  size 
in  different  individuals. 

Structure. — The  gland  is  encased  in  a  thin  transparent  layer  of  dense 
areolar  tissue,  free  from  fat,  containing  elastic  fibres.  This  capsule  sends 
in  strong  fibrous  trabeculse,  which  enclose  the  thyroid  vesicles — which  are 
rounded  or  oblong  irregular  sacs,  consisting  of  a  wall  of  thin  hyaline 
membrane  lined  by  a  single  layer  of  low  cylindrical  or  cubical  cells. 
These  vesicles  are  filled  with  a  coagulable  fluid  or  transparent  colloid 
material.  The  colloid  substance  increases  with  age,  and  the  cavities 
appear  to  coalesce.  In  the  interstitial  connective  tissue  is  a  round  meshed 


8 


HAND-BOOK  OF  PHYSIOLOGY. 


capillary  plexus  and  a  large  number  of  lymphatics.  The  nerves  adhere 
closely  to  the  vessels. 

In  the  vesicles  there  are  in  addition  to  the  yellowish  glassy  colloid 
material,  epithelium  cells,  colorless  blood  corpuscles,  and  also  colored  cor- 
puscles undergoing  disintegration. 

Function. — There  is  little  known  definitely  about  the  function  of  the 
thyroid  body.  It,  however,  produces  the  colloid  material  of  the  vesicles, 
which  is  carried  off  by  the  lymphatics  and  discharged  into  the  blood,  and 
so  may  contribute  its  share  to  the  elaboration  of  that  fluid.  The  destruc- 
tion of  red  blood-corpuscles  is  also  supposed  to  go  on  in  the  gland. 

SUPRA-EEKAL  CAPSULES  OR  AdRENALS. 

These  are  two  flattened,  more  or  less  triangular  or  cocked-hat  shaped 
bodies,  resting  by  their  lower  border  upon  the  upper  border  of  the 
kidneys. 

Structure. — The  gland  is  surrounded  by  an  outer  sheath  of  connec- 
tive tissue,  which  sometimes  consists  of  two  layers,  sending  in  exceedingly 


Fig.  258.— Vertical  section  through  part  of  the  cortical  portion  of  supra-renal  of  guinea-pig.  a, 
capsule;  6,  zonaglomerulosa;  c,  zona  fasciculata;  d,  connective  tissue  supporting  the  columns  of  the 
cells  of  the  latter,  and  also  indicating  the  position  of  the  blood-vessels.   (S.  K.  Alcock.) 

fine  prolongations  forming  the  framework  of  the  gland.  The  gland  tissue 
proper  consists  of  an  outside  firmer  cortical  portion,  and  an  inside  soft 
dark  medullary  portion.  (1.)  The  cortical  portion  is  divided  into  (Fig. 
258  b)  an  external  narrow  layer  of  small  rounded  or  oval  spaces,  the  zona 
glomerutosa,  made  by  the  fibrous  trabecula?,  containing  multinucleated 


THE  VASCULAR  GLANDS. 


9 


masses  of  protoplasm,  the  differentiation  of  which  into  distinct  cells  cannot 
be  made  out.  {h)  A  layer  of  cells  arranged  radially,  the  zona  fasciculata  {c). 
The  substance  of  this  layer  is  broken  up  into  cylinders,  each  of  which  is 
surrounded  by  the  connective -tissue  framework.  The  cylinders  thus  pro- 
duced are  of  three  kinds — one  containing  an  opaque,  resistant,  highly 
refracting  mass  (probably  of  a  fatty  nature);  frequently  a  large  number 
of  nuclei  are  present;  the  individual  cells  can  only  be  made  out  with  diffi- 
culty. The  second  variety  of  cylinders  is  of  a  brownish  color,  and  con- 
tains finely  granular  cells,  in  which  are  fat  globules.  The  third  variety 
consists  of  grey  cylinders,  containing  a  number  of  cells  whose  nuclei  are 
filled  with  a  large  number  of  fat  granules.  The  third  layer  of  the  corti- 
cal portion  is  the  zona  reticularis  (not  shown  in  Fig.  258).  This  layer  is 
apparently  formed  by  the  breaking  up  of  the  cylinders,  the  elements  being 


Fig.  259.— Section  through  a  portion  of  the  medullary  part  of  the  supra-renal  of  guinea-pig.  The 
vessels  are  very  numerous,  and  the  fibrous  stroma  more  distinct  than  in  the  cortex,  and  is  moreover 
reticulated.   The  cells  are  irregular  and  larger,  clean,  and  free  from  oil  globules.   (S.  K.  Alcock.) 

dispersed  and  isolated.  The  cells  are  finely  granular,  and  have  no 
deposit  of  fat  in  their  interior;  but  in  some  specimens  fat  may  be  pres- 
ent, as  well  as  certain  large  yellow  granules,  which  may  be  called  pig- 
ment granules. 

(2.)  The  medullary  substance  consists  of  a  coarse  rounded  or  irregular 
meshwork  of  fibrous  tissue,  in  the  alveoli  of  which  are  masses  of  multi- 
nucleated protoplasm  (Fig.  259);  numerous  blood-vessels;  and  an  abun- 
dance of  nervous  elements.  The  cells  are  very  irregular  in  shape  and  size, 
poor  in  fat,  and  occasionally  branched;  the  nerves  run  through  the  corti- 
cal substance,  and  anastomose  over  the  medullary  portion. 

Function. — Of  the  function  of  the  supra-renal  bodies  nothing  can  be 
definitely  stated,  but  they  are  in  all  probability  connected  with  the  lym- 
phatic system. 


10 


HAND-BOOK  OF  PHYSIOLOGY. 


Addison's  Disease. — The  collection  of  large  numbers  of  cases  in  which 
the  supra-renal  capsules  have  been  diseased,  has  demonstrated  the  very 
close  relation  subsisting  between  disease  of  those  organs  and  brown  dis- 
coloration of  the  skin  (Addison's  disease);  but  the  explanation  of  this 
relation  is  still  involved  in  obscurity,  and  consequently  does  not  aid  much 
in  determining  the  functions  of  the  supra-renal  capsules. 

PiTuiTAKY  Body. 

This  body  is  a  small  reddish- grey  mass,  occupying  the  sella  turcica  of 
the  sphenoid  bone. 

Structure. — It  consists  of  two  lobes — a  small  posterior  one,  consist- 
ing of  nervous  tissue;  an  anterior  larger  one,  resembling  the  thyroid  in 
structure.  A  canal  lined  with  flattened  or  with  ciliated  epithelium,  passes 
through  the  anterior  lobe;  it  is  connected  with  the  infundibulum.  The 
gland  spaces  are  oval,  nearly  round  at  the  periphery,  spherical  toward  the 
centre  of  the  organ;  they  are  filled  with  nucleated  cells  of  various  sizes 
and  shapes  not  unlike  ganglion  cells,  collected  together  into  rounded 
masses,  filling  the  vesicles,  and  contained  in  a  semi-fluid  granular  sub- 
stance. The  vesicles  are  enclosed  by  connective  tissue  rich  in  capil- 
laries. 

Function. — Nothing  is  known  of  the  function  of  the  pituitary  body. 
Pineal  Gland. 

This  gland,  which  is  a  small  reddish  body,  is  placed  beneath  the  back 
part  of  the  corpus  callosum,  and  rests  upon  the  corpora  quadrigemina 
(Fig.  327,  g). 

Structure. — It  contains  a  central  cavity  lined  with  ciliated  epithe- 
lium. The  gland  substance  proper  is  divisible  into — (1.)  An  outer  corti- 
cal layer,  analogous  in  structure  to  the  anterior  lobe  of  the  pituitary  body; 
and  (2)  An  inner  central  layer,  wholly  nervous.  The  cortical  layer  con- 
sists of  a  number  of  closed  follicles,  containing  (a)  cells  of  variable  shape, 
rounded,  elongated,  or  stellate;  (b)  fusiform  cells.  There  is  also  present 
a  gritty  matter  (acervulus  cerebri),  consisting  of  round  particles  aggre- 
gated into  small  masses.  The  central  substance  consists  of  white  and  grey 
matter.  The  blood-vessels  are  small,  and  form  a  very  delicate  capillary 
plexus. 

Function. — Of  this  there  is  nothing  known. 

Functions  of  the  Vascular  Glands  in  General. 

The  opinion  that  the  vascular  glands  serve  for  the  higher  organization 
of  the  blood,  is  supported  by  their  being  all  especially  active  in  the  dis- 
charge of  tlieir  functions  during  fa3tal  life  and  childliood,  when,  for  the 


THE  VASCULAR  GLANDS. 


11 


development  and  growth  of  the  body,  the  most  abundant  supply  of  highly 
organized  blood  is  necessary.  The  bulk  of  the  thymus  gland,  in  propor- 
tion to  that  of  the  body,  appears  to  bear  almost  a  direct  proportion  to  the 
activity  of  the  body's  development  and  growth,  and  when,  at  the  period 
of  puberty,  the  development  of  the  body  may  be  said  to  be  complete,  the 
gland  wastes,  and  finally  disappears.  The  thyroid  gland  and  supra-renal 
capsules,  also,  though  they  probably  never  cease  to  discharge  some  amount 
of  function,  yet  are  proportionally  much  smaller  in  childhood  than  in  foetal 
life  and  infancy;  and  with  the  years  advancing  to  the  adult  period,  they 
diminish  yet  more  in  proportionate  size  and  apparent  activity  of  function. 
The  spleen  more  nearly  retains  its  proportionate  size,  and  enlarges  nearly 
as  the  whole  body  does. 

The  vascular  glands  seem  not  essential  to  life,  at  least  not  in  the 
adult.  The  thymus  wastes  and  disappears:  no  signs  of  illness  attend  some 
of  the  diseases  which  wholly  destroy  the  structure  of  the  thyroid  gland; 
and  the  spleen  has  been  often  removed  in  animals,  and  in  a  few  instances 
in  men,  without  any  evident  ill-consequence.  It  is  possible  that,  in  such 
cases,  some  compensation  for  the  loss  of  one  of  the  organs  may  be  afforded 
by  an  increased  activity  of  function  in  those  that  remain. 

Although  the  functions  of  all  the  vascular  glands  may  be  similar,  in 
so  far  as  they  may  all  alike  serve  for  the  elaboration  and  maintenance  of 
the  blood,  yet  each  of  them  probably  discharges  a  peculiar  office,  in  rela- 
tion  either  to  the  whole  economy,  or  to  that  of  some  otliet  organ.  Ee- 
specting  the  special  office  of  the  thyroid  gland,  nothing  reasonable  can  be 
suggested;  nor  is  there  any  certain  evidence  concerning;  that  of  the  supra- 
renal capsules.  Bergman  believed  that  they  formed  part  of  the  sympa- 
thetic nervous  system  from  the  richness  of  their  nervous  supply.  Kolliker 
states  that  he  is  inclined  to  look  upon  the  two  parts  as  functionally  dis- 
tinct, the  cortical  part  belonging  to  the  blood  vascular  system,  and  the 
medullary  to  the  nervous  system. 


CHAPTER  XV. 


CAUSES  AND  PHENOMENA  OF  MOTION. 


IiT  the  animal  body,  motion  is  produced  in  these  several  ways:  (1.) 
The  oscillatory  or  vibratory  movement  of  Cilia,  (2.)  Amosioid  and  certain 
Molecular  moYements.    (3.)  The  contrsLction  ot  Muscular  fibre. 


Ciliary,  which  is  closely  allied  to  amoeboid  and  muscular  motion  (p.  8, 
Vol.  I.),  consists  in  the  incessant  vibration  of  fine,  pellucid  processes,  about 
-g^g-g-  of  an  inch  long,  termed  cilia  (Figs.  260,  261,)  situated  on  the  free 
extremities  of  the  cells  of  epithelium  covering  certain  surfaces  of  the  body. 

The  distribution  and  structure  of  ciliary  epithelium  and  the  micro- 
scopic appearances  of  cilia  in  motion  have  been  already  described  (pp. 
25,  26,  Vol.  L). 

Ciliary  motion  is  alike  independent  of  the  will,  of  the  direct  influ- 
ence of  the  nervous  system,  and  of  muscular  contraction.  It  continues 
for  several  hours  after  death  or  removal  from  the  body,  provided  the 


Fig.  260.— Spheroidal  ciliated  cells  from  the  mouth  of  the  frog;  magnified  300  diameters, 

(Sharpey.) 

Fig.  261.— Columnar  ciliated  cells  from  the  human  nasal  membrane:  magnified  300  diameters. 
(Sharpey.) 

portion  of  tissue  under  examination  bo  kept  moist.  Its  independence  of 
the  nervous  system  is  sliown  also  in  its  occurrence  in  the  lowest  inverte- 
brate animals  apparently  unprovided  with  anything  analogous  to  a  nervous 
system,  in  its  persistence  in  animals  killed  by  prussic  acid,  by  narcotic  or 
other  poisons,  and  after  the  direct  application  of  narcotics  to  the  ciliary  sur- 


I.  Ciliary  Motion. 


Fig.  260. 


Fig.  261. 


CAUSES  AND  PHENOMENA  OF  MOTION. 


13 


face,  or  the  discharge  of  a  Leyden  jar,  or  of  a  galvanic  shock  throngh  it. 
The  vapor  of  chloroform  arrests  the  motion;  but  it  is  renewed  on  the  dis- 
continuance of  the  application  (Lister).  The  movement  ceases  in  an  at- 
mosphere deprived  of  oxygen,  but  is  revised  on  the  admission  of  this  gas. 
Carbonic  acid  stops  the  movement.  The  contact  of  various  substances 
will  stop  the  motion  altogether;  but  this  seems  to  depend  chiefly  on 
destruction  of  the  delicate  substance  of  which  the  cilia  are  composed. 

Nature  of  Ciliary  Action. — Little  or  nothing  is  known  with  cer- 
tainty regarding  the  nature  of  ciliary  action.  It  is  a  special  manifestation 
of  a  similar  property  to  that  by  which  the  other  motions  of  animals  are 
effected,  namely,  by  what  we  term  vital  contractility  (Sharpey).  The 
fact  of  the  more  evident  movements  of  the  larger  animals  being  effected 
by  a  structure  apparently  different  from  that  of  cilia,  is  no  argument 
against  such  a  supposition.  For,  if  we  consider  the  matter,  it  will  be 
plain  that  our  prejudices  against  admitting  a  relationship  to  exist  between 
the  two  structures,  muscles  and  cilia,  rests  on  no  definite  ground;  and 
for  the  simple  reason,  that  we  know  so  little  of  the  manner  of  production 
of  movement  in  either  case.  The  mere  difference  of  structure  is  not  an 
argument  in  point;  neither  is  the  presence  or  absence  of  nerves.  For  in 
the  foetus  the  heart  begins  to  pulsate  when  it  consists  of  a  mass  of  em- 
bryonic cells,  and  long  before  either  muscular  or  nervous  tissue  has  been 
differentiated.  The  movements  of  both  muscles  and  cilia  are  manifesta- 
tions of  energy,  by  certain  special  structures,  which  we  call  respectively 
muscles  and  cilia.  We  know  nothing  more  about  the  means  by  which 
the  manifestation  is  effected  by  one  of  these  structures  than  by  the  other: 
and  the  mere  fact  that  one  has  nerves  and  the  other  has  not,  is  no  more 
argument  against  cilia  having  what  we  call  a  vital  power  of  contraction, 
than  the  presence  or  absence  of  stripes  from  voluntary  or  involuntary 
muscles  respectively,  is  an  argument  for  or  against  the  contraction  of  one 
of  them  being  vital  and  the  other  not  so. 

As  a  special  subdivision  of  ciliary  action  may  be  mentioned  the  motion 
of  spermatozoa  (Fig.  403),  which  may  be  regarded  as  cells  with  a  single 
cilium. 

II.  Amceboid  Motion. 

The  remarkable  movements  observed  in  colorless  blood  corpuscles, 
connective-tissue  corpuscles,  and  many  other  cells  (p.  8,  Vol.  I.),  must  be 
regarded  as  depending  on  a  kind  of  contraction  of  portions  of  their  mass 
very  similar  to  muscular  contraction. 

There  is  certainly  an  analogy  between  the  spherical  form  assumed  by  a 
colorless  blood-corpuscle  on  electric  stimulation  and  the  condition  known 
as  tetanus  in  muscles. 


14 


HAND-BOOK  OF  PHYSIOLOGY. 


III.  MuscuLAE  Motion. 

Varieties  of  Muscular  Tissue. —  There  are  two  chief  kinds  of 
muscular  tissue:  (1.)  the  plain  or  non-striated,  arid  (2.)  the  striated,  and 
they  are  distinguished  by  structural  peculiarities  and  mode  of  action. 
The  striped  form  of  muscular  fibre  is  sometimes  called  mluntary  muscle, 
because  all  muscles  under  the  direct  control  of  the  will  are  constructed  of 
it.  The  plain  or  unstriped  variety  is  often  termed  involuntary,  because 
it  alone  is  found  in  the  greater  number  of  the  muscles  over  which  the 
will  has  no  power. 

(1.)  Plain  oe  Unsteiped  Muscle. 

Distribution. — Involuntary  muscle  forms  the  proper  muscular  coats 
(1.)  of  the  digestive  canal  from  the  middle  of  the  oesophagus  to  the  inter- 
nal sphincter  ani;  (2.)  of  the  ureters  and  urinary  bladder;  (3.)  the  trachea 
and  bronchi;  (4.)  the  ducts  of  glands;  (5.)  the  gall-l)ladder;  (6.)  the 
vesiculge  seminales;  (7.)  the  pregnant  uterus;  (8.)  of  blood-vessels  and 
lymphatics;  (9.)  the  iris,  and  some  other  parts.    This  form  of  tissue  also 


Fig.  262.— Vertical  section  through  the  scalp  with  two  hair-sacs;  a,  epidermis;  6,  cutis;  c,  muscles 
of  the  hair-foUicles.  (Kolliker.) 

enters  (10.)  largely  into  the  composition  of  the  tunica  dartos,  and  is  the 
principal  cause  of  the  wrinkling  and  contraction  of  the  scrotum  on  expo- 
sure to  cold.  Unstriped  muscular  tissue  occurs  largely  also  (11. )  in  the  cutis 
(p.  335,  Vol.  I.),  being  especially  abundant  in  the  interspaces  between 
the  bases  of  the  papillae.  Hence  when  it  contracts  under  the  influence  of 
cold,  fear,  electricity,  or  any  other  stimulus,  tlie  papillae  are  made  unusually 
prominent,  and  give  rise  to  the  peculiar  roughness  of  the  skin  termed 
cutis  anserina,  or  goose  skin.  It  occurs  also  in  the  superficial  portion  of 
the  cutis,  in  all  parts  where  hairs  occur,  in  the  form  of  flattened  roundish 
bundles,  whicli  lie  alongside  the  hair-follicles  and  sebaceous  glands.  Tliey 
pass  obliquely  from  without  inward,  embrace  the  sebaceous  glands,  and 
are  attached  to  the  hair-follicles  near  their  base  (Fig.  228). 


CAUSES  AND  PHENOMENA  OF  MOTION. 


15 


Structure. — The  non-striated  muscles  are  made  up  of  elongated, 
spindle-shaped,  nucleated,  fibre  cells  (Fig.  263),  which  in  their  perfect 
form  are  flat,  from  about  ^^Vo  j^^^tf  c>f  an  inch  broad,  and  to  -g-J-g-  of 
an  inch  in  length, — very  clear,  granular,  and  brittle,  so  that  when  they 


Fig.  263. — A,  unstriped  muscle  cells  from  mesentery  of  newt,  sheath  with  transverse  marking 
faintly  seen.  X  180.  B,  from  similar  preparation,  showing  each  muscle  cell  consists  of  a  central 
bundle  of  fibrils  (contractile  part)  connected  with  the  intranuclear  network  and  a  sheath  with  annu- 
lar thickenings.  The  cells  show  varicosities  due  to  local  contraction,  and  on  these  the  annular  thick- 
enings are  most  marked.    X  450.   (Klein  and  Noble  Smith.) 

break  they  often  have  abruptly  rounded  or  square  extremities.  Each 
muscle  cell  consists  of  a  fine  sheath,  probably  elastic;  of  a  central  bundle 
of  fibrils  representing  the  contractile  substance;  and  of  an  oblong  nucleus 
which  includes  within  a  membrane  a  fine,  network  anastomosing  at  the 
poles  of  the  nucleus  with  the  contractile  fibrils.    The  ends  of  fibres 


Fig.  264. 


-Plexus  of  bundles  of  unstriped  muscle  cells  of  the  pulmonary  pleura  of  the  guinea-pig 
X  180.   (Klein  and  Noble  Smith.) 


are  usually  single,  sometimes  divided.  Between  the  fibres  is  an  albumi- 
nous cementing  material  (endomysium)  in  which  are  found  connective- 
tissue"  corpuscles,  and  a  few  fibres.  The  perimysium  is  the  fibrous  con- 
nective tissue  surrounding  and  separating  the  bundles  of  muscle  cells. 

(2.)  Stkiated  ok  Steiped  Muscle. 

Distribution. — The  striated  muscles  include  the  whole  class  of  vol- 
untary muscles,  the  heart,  and  those  muscles  neither  completely  volun- 


16 


HAND-BOOK  OF  PHYSIOLOGY. 


tary  nor  involuntary,  which  form  part  of  the  walls  of  the  pharynx,  and 
exist  in  many  other  parts  of  the  body,  as  the  internal  ear,  urethra,  etc. 

Structure. — All  these  muscles  are  composed  of  larger  or  smaller 
bundles  of  muscular  fibres  called  fasciculi,  enclosed  in  coverings  of  fibro- 
cellular  tissue  {perimysium),  by  which  each  is  at  once  connected  with 
and  isolated  from  those  adjacent  to  it  (Fig.  265).  Supporting  the  fibres 
contained  in  each  fasciculus  is  a  scanty  amount  of  fine  connective  tissue 
endomysium. 

Each  muscular  fibre  is  thus  constructed: — Externally  is  a  fine,  trans- 
parent, structureless  membrane,  called  the  sarcolemma  (Fig.  266,  A), 
which  in  the  form  of  a  tubular  investing  sheath  forms  the  outer  wall  of 


Fig.  265.  Fig.  266. 


Fig.  265.— a  small  portion  of  muscle  natural  size,  consisting  of  larger  and  smaller  fasciculi,  ocjen 
in  a  transverse  section,  and  the  same  magnified  5  diameters.  (Sharpey.) 

Fig.  266.— Part  of  a  striped  muscle-fibre  of  a  water-beetle  (hydrophilus)  prepared  with  absolute 
alcohol.  A,  sarcolemma;  B,  Krause's  membrane.  Owing  to  contraction  during  hardening,  the  sar- 
colemma shows  regular  bulgings.  Above  and  below  Krause's  membrane  are  seen  the  transparent 
"lateral  discs.""  The  chief  mass  of  a  muscular  compartment  is  occupied  by  the  contractile  disc  com- 
posed of  sarcous  elements.  The  substance  of  the  individual  sarcous  elements  has  collected  more  at 
the  extremity  than  in  the  centre:  hence  this  latter  is  more  transparent.  The  optical  effect  of  this  is 
that  the  contractile  disc  appears  to  possess  a  "median  disc"  (Disc  of  Hensen).  Several  nuclei  of 
muscle  corpuscles,  C  and  D,  are  shown,  and  in  them  a  minute  network,  x  300.  (Klein  and  Noble 
Smith.) 

the  fibre,  and  is  filled  up  by  the  contractile  material  of  which  the  fibre  is 
chiefly  composed.  Sometimes,  from  its  comparative  toughness,  the  sarco- 
lemma will  remain  untorn,  when  by  extension  the  contained  part  can  be 
broken  (Fig.  269),  and  its  presence  is  in  this  way  best  demonstrated. 
The  fibres,  which  are  cylindriform  or  prismatic,  with  an  average  diameter 
of  about  of  an  inch,  are  of  a  pale  yellow  color,  and  apparently  marked 
by  fine  striae,  which  pass  transversely  round  them,  in  slightly  curved  or 
wholly  parallel  lines.  Each  fibre  is  found  to  consist  of  broad  dim  bands 
of  highly  refractive  substance  representing  the  contractile  portion  of  the 
muscle  fibre — tlie  contractile  discs  (Fig.  267,  A,  c) — alternating  Avith  nar- 
row bright  bands  of  a  less  refractive  substance — the  interstitial  discs 
(Fig.  267,  A,  i).  After  hardening,  each  contractile  disc  becomes  longi- 
tudinally striated,  the  thin  oblong  rods  tlius  formed  being  the  sarcous 
elements  of  ]k)wmau.  The  sarcous  elements  are  not  the  optical  units, 
since  each  consists  of  minute  doubly-refracting  elements — the  disdiaclasts 


CAUSES  AND  PHENOMENA  OF  MOTION. 


17 


of  Briicke.  When  seen  in  transverse  section  the  contractile  discs  appear 
to  be  subdivided  by  clear  lines  into  polygonal  areas,  Cohnheim's  fields 
(Fig.  271),  each  corresponding  to  one  sarcous  element  prism.  The  clear 
lines  are  due  to  a  transparent  interstitial  fluid  substance  pressed  out  of 
the  sarcous  elements  when  they  coagulate.  There  is  still  some  doubt 
regarding  the  nature  of  the  fibrils.  Each  of  them  appears  to  be  com- 
posed of  a  single  row  of  minute  dark  quadrangular  particles,  called  sarcous 
elements,  which  are  separated  from  each  other  by  a  bright  space  formed 
of  a  pellucid  substance  continuous  with  them.  Sharpey  believes  that, 
even  in  a  fibril  so  constituted,  the  ultimate  anatomical  element  of  the 
fibre  has  not  been  isolated.  He  believes  that  each  fibril  with  quadrangular 


Fig.  267.— a.  Portion  of  a  medium-sized  hvmian  muscular  fibre,  x  800.  B.  Separated  bundles 
of  fibrils  ec[uaUy  magnified;  a,  a,  larger,  and  6,  6,  smaUer  coUections;  c,  still  smaller;  d,  d,  the 
smallest  which  could  be  detached,  possibly  representing  a  single  series  of  sarcous  elements.  (Sharpey.) 

sarcous  elements  is  composed  of  a  number  of  other  fibrils  still  finer,  so  that 
the  sarcous  element  of  an  ultimate  fibril  would  be  not  quadrangular,  but 
as  a  streak.  In  either  case  the  appearance  of  striation  in  the  whole  fibre 
would  be  produced  by  the  arrangement,  side  by  side,  of  the  dark  and 
light  portions  respectively  of  the  fibrils  (Fig.  267,  B,  d). 

A  fine  streak  can  usually  be  discerned  passing  across  the  interstitial 
disc  between  the  sarcous  elements:  this  streak  is  termed  Krause^s  mem- 
brane: it  is  continuous  at  each  end  with  the  sarcolemma  investing  the 
muscular  fibre  (Fig.  266,  B). 

Thus  the  space  enclosed  by  the  sarcolemma  is  divided  into  a  series  of 
compartments  by  the  transverse  partitions  known  as  Krause^s  membranes; 
these  compartments  being  occupied  by  the  true  muscle  substance.  On 
Vol.  II.— 3. 


18  HAND-BOOK  OF  PHYSIOLOGY. 

each  side  (above  and  below)  of  Krause's  membrane  is  a  bright  border 
(lateral  disc).  In  the  centre  of  the  dark  zone  of  sarcous  elements  a  lighter 
band  can  sometimes  be  dimly  discerned:  this  is  termed  the  middle  disc 
of  Hensen  (see  Fig.  266,  A). 

In  some  fibres,  chiefly  those  from  insects,  each  lateral  disc  contains  a 
row  of  bright  granules  forming  the  granular  layer  of  Flogel.    The  fibres 


(Todd  and  Bowman.) 

contain  nuclei,  which  are  roundish  ovoid,  or  spindle-shaped  in  different 
animals.  These  nuclei  are  situated  close  to  the  sarcolemma,  their  long 
axes  being  parallel  to  the  fibres  which  contain  them.  Each  nucleus  is 
composed  of  a  uniform  network  of  fibrils,  and  is  embedded  in  a  thin. 


Fig.  270.  Fig.  271. 


Fig.  270.— Section  through  the  muscular  substance  of  the  tongue,  with  capillaries  injected,  their 
meshes  running  parallel  to  the  fibres.  Three  muscular  fibres  are  seen  running  longitudinally,  and 
two  bundles  of  fibres  in  transverse  section.    X  150.    (Klein  and  Nc^ble  Snuth.') 

Fig.  271.— Transverse  section  through  muscular  fibres  of  human  tongue;  the  fibres  appear  in 
transverse  section  of  dilTerent  sizes  owing  to  their  being  more  or  h'ss  s]iin(ll(^-shaped.  The  muscle- 
corpuscles  are  indicated  by  their  deeply-stained  nuclei  situated  at  (he  inside  of  tlie  sarcolenuua. 
Each  muscle-fibre  shows  the  "Cohnheini's  fields,"  that  is  the  sareons  eltMuents  in  transverse  section 
separated  by  clear  (apparently  linear)  interstitial  substance.    X  450.     Klein  and  Noble  Smith.) 

more  or  less  branched  film  of  protoplasm.  The  nncleus  and  protoi)lasm 
together  form  the  muscle  cell  or  muscle  corpuscle  of  ^fax  Scluiltzo. 

The  sarcous  elements  and  Krause's  membranes  are  doubly  refracting, 
the  rest  of  the  fibre  singly  refracting  (l^riickc). 


CAUSES  AKD  PHENOMENA  OF  MOTION. 


19 


According  to  Schafer,  the  granules,  which  have  been  mentioned  on 
either  side  of  Krause's  membrane,  are  little  knobs  attached  to  the  ends  of 
"muscle-rods;"'  and  these  muscle-rods,  knobbed  at  each  end  and  imbedded 
in  a  homogeneous  protoplasmic  ground-substance,  form  the  substance  of 
the  muscles.  This  view,  however,  of  the  structure  of  muscle  requires 
further  confirmation  before  it  can  be  accepted. 

Although  each  muscular  fibre  may  be  considered  to  be  formed  of  a 
number  of  longitudinal  fibrils,  arranged  side  by  side,  it  is  also  true  that 
they  are  not  naturally  separate  from  each  other,  there  being  lateral 
cohesion,  if  not  fusion,  of  each  sarcous  element  with  those  around  and  in 
contact  with  it;  so  that  it  happens  that  there  is  a  tendency  for  a  fibre  to 


Fig.  272.— Muscular  fibres  from  the  heart,  magnified,  showing  their  cross-striae,  divisions,  and 
junctions.  (Kolliker.) 

Fia.  273. — Network  of  muscular  fibres  (striated)  from  the  heart  of  a  pig.  The  nuclei  of  the  mus- 
cle-corpuscles are  well  shown,    x  450.   (Klein  and  Noble  Smith.) 

split,  not  only  into  separate  fibrils,  but  also  occasionally  into  plates  or 
discs,  each  of  which  is  composed  of  sarcous  elements  laterally  adherent 
one  to  another. 

Muscular  Fibres  of  the  Heart  (Figs.  272  and  273)  form  the  chief, 
though  not  the  only  except-ion  to  the  rule,  that  involuntary  muscles  are 
constructed  of  plain  fibres;  but  although  striated  and  so  far  resembling 
those  of  the  skeletal  muscles,  they  present  these  distinctions: — Each 
muscular  fibre  is  made  up  of  elongated,  nucleated,  and  branched  cells, 
the  nuclei  or  muscle-corpuscles  being  centrally  placed  in  the  fibre.  The 
fibres  are  finer  and  less  distinctly  striated  than  those  of  the  voluntary 
muscles;  and  no  sarcolemma  can  be  usually  discerned. 

Blood  and  Nerve  Supply. — The  voluntary  muscles  are  freely  sup- 
plied with  blood-vessels;  the  capillaries  form  a  network  with  oblong 


Fig.  272. 


Fig.  27i 


20 


HAND-BOOK  OF  PHYSIOLOGY. 


meshes  around  the  fibres  on  the  outside  of  the  sarcolemma.  No  vessels 
penetrate  tlie  sarcolemma  to  enter  the  interior  of  the  fibre  (Fig.  270). 
Nerves  also  are  supplied  freely  to  muscles  (pp.  76,  80,  Vol.  II.);  the  volun- 
tary muscles  receiving  chiefly  nerves  from  the  cerebro-spinal  system,  and 
the  unstriped  muscles  from  the  sympathetic  or  ganglionic  system. 


Fig.  274— Muscular  fibre  cells  from  the  heart.   (E.  A.  Schafer.) 

Development. — (1.)  Unstriped. — The  cells  of  unstriped  muscle  are 
derived  directly  from  embryonic  cells,  by  an  elongation  of  the  cell,  and 
its  nucleus;  the  latter  changing  from  a  vascular  to  a  rod  shape. 

(2.)  Striped. — Formerly  it  was  supposed  that  striated  fibres  are  formed 
by  the  coalescence  of  several  cells,  but  recently  it  has  been  proved,  that 
each  fibre  is  formed  from  a  single  cell,  the  process  involving  an  enormous 
increase  in  size,  a  multiplication  of  the  nucleus  by  fission,  and  a  differen- 
tiation of  the  cell-contents  (Eemak,  Wilson  Fox).  This  view  differs  but 
little  from  that  previously  taken  by  Savory,  that  the  muscular  fibre  is 
produced,  not  by  multiplication  of  cells,  but  by  arrangement  of  nuclei  in 
a  growing  mass  of  protoplasm  (answering  to  the  cell  in  the  theory  just 
referred  to),  which  becomes  gradually  differentiated  so  as  to  assume  the 
characters  of  a  fully  developed  muscular  fibre. 

Growth  of  Muscle. — The  growth  of  muscles,  both  striated  and  non- 
striated,  is  the  result  of  an  increase  both  in  the  number  and  size  of  the 
individual  elements. 

In  the  pregnant  uterus  the  fibre-cells  may  become  enlarged  to  ten 
times  their  original  length.  In  involution  of  the  uterus  after  parturition 
the  reverse  changes  occur,  accompanied  generally  by  some  fatty  infil- 
tration of  the  tissue  and  degeneration  of  the  fibres. 

Physio  L<)(}Y  of  Muscu.e. 
Muscle  may  exist  in  three  different  conditions:  restf  arfivify,  and  rigor. 


CAUSES  AND  PHENOJMENA  OF  MOTION. 


21 


I.  Eest. 

Physical  Condition. — During  rest  or  inactivity  a  muscle  has  a  slight 
but  very  perfect  elasticity;  it  admits  of  being  considerably  stretched;  but 
returns  readily  and  completely  to  its  normal  length.  In  the  living  body  the 
muscles  are  always  stretched  somewhat  beyond  their  natural  length,  they 
are  always  in  a  condition  of  slight  tension;  an  arrangement  which  enables 
the  whole  force  of  the  contraction  to  be  utilized  in  a^jproximating  the 
points  of  attachment.  It  is  obvious  that  if  the  muscles  were  lax,  the  first 
part  of  the  contraction  till  the  muscle  became  tight  would  be  wasted. 

There  is  no  doubt  that  even  in  a  condition  of  rest  oxygen  is  being 
alstr  acted  from  the  Hood  and  carbonic  acid  given  out  by  a  muscle;  for  the 
blood  becomes  venous  in  the  transit,  and  since  the  muscles  form  by  far 
the  largest  element  in  the  composition  of  the  body,  chemical  changes 
must  be  constantly  going  on  in  them  as  in  other  tissues  and  organs, 
although  not  necessarily  accompanied  by  contraction.  When  cut  out  of 
the  body  such  muscles  retain  their  contractility  longer  in  an  atmosphere 
of  oxygen  than  in  an  atmosphere  of  hydrogen  or  carbonic  acid,  and  during 
life,  an  amount  of  oxygen  is  no  doubt  necessary  to  the  manifestation  of 
energy  as  well  as  for  the  metabolism  going  on  in  the  resting  condition. 

Chemical  composition. — The  reaction  of  living  muscle  is  neutral  or 
slightly  cdhaline.  The  substance  or  muscle  plasma  which  forms  the  con- 
tractile principal  element  in  its  composition  undergoes  coagulation  when 
the  muscle  is  removed  from  the  body,  and  the  process  may  be  observed 
if  the  coagulation  be  delayed  by  cold.  If  the  muscles  of  a  frog  be  frozen, 
minced  whilst  in  that  condition,  and  reduced  to  a  pulp  by  being  rubbed 
up  with  a  1  per  cent,  solution  of  sodium  chloride,  the  temperature  of 
which  must  be  very  low,  on  filtration  in  the  cold,  a  colorless,  somewhat 
turbid  filtrate  separates  with  difficulty,  which  is  muscle  plasma.  This 
fluid  at  the  ordinary  temperature  of  the  air  undergoes  a  coagulation  or 
clotting,  by  which  it  is  separated,  as  in  the  case  of  blood,  into  muscle- 
serum,  and  muscle-clot.  The  latter,  however,  is  not  made  up  of  fibrin  but  of 
myosin,  which  is  a  globulin  (p.  328,  Vol.  II. ).  Myosin  may  also  be  obtained 
from  dead  muscle  by  subjecting  it,  after  all  the  blood,  fat,  fibrous  tissue, 
and  substances  soluble  in  water,  have  been  removed,  to  a  ten  per  cent, 
solution  of  sodium  chloride,  filtering  and  allowing  the  filtrate  to  drop  into 
a  large  quantity  of  water;  myosin  separating  out  as  a  white  flocculent 
precipitate.  Obtained  in  either  way,  viz.,  from  living  or  dead  muscle, 
myosin  is  soluble  in  dilute  saline  solutions,  and  the  solution  undergoes 
coagulation  at  a  lower  temperature  than  serum-albumin  or  paraglobulin, 
viz.,  at  131°— 140°  F.  (55°— 60°  0.).  It  is  coagulated  also  by  alcohol. 
It  is  dissolved  and  converted  into  acid-albumin  by  dilute  acid,  such  as 
hydrochloric. 


22 


HAND-BOOK  OF  PHYSIOLOGY. 


Muscle-serum  is  acid  in  reaction,  contains  serum-albumin  and  several 
other  proteids  as  well  as  other  bodies,  among  which  are  fats;  free  acids, 
especially  sarco-lactic,  formic,  and  acetic;  glucose,  glycogen  and  inosite; 
kreatin,  hypoxanthin,  or  carnin,  taurin,  and  other  nitrogenous  crystalline 
bodies;  many  salts,  of  which  the  chief  is  potassium  phosphate;  Carbonic 
acid,  and  lastly  Haemoglobin,  on  which  the  color  of  muscles  partially 
depends.    There  are  also  traces  of  ferments,  pepsin  among  others. 

Electrical  Condition;  Natural  muscle  currents. — In  muscles  which 
have  been  removed  from  the  body,  it  has  been  found  that  electrical  cur- 
rents can  be  demonstrated  for  some  little  time,  passing  from  point  to 
point  on  their  surface;  but  as  soon  as  the  muscles  die  or  enter  into  rigor 
mortis,  these  currents  disappear.    The  method  of  demonstration  usually 


Fig.  275.— Diagram  of  Du  Bois  Reymond's  non-polarizable  electrodes,  a,  glass  tube  filled  with  a 
saturated  solution  of  zinc  sulphate,  in  the  end,  c,  of  which  is  china  clay  drawn  out  to  a  point ;  in  the 
solution  a  weU  amalgamated  zinc  rod  is  immersed  and  comiected  by  means  of  the  wire  which  passes 
through  A  with  the  galvanometer.  The  remainder  of  the  apparatus  is  simply  for  convenient  apphca- 
tion.   The  muscle  to  the  end  of  the  second  electrode  is  to  the  right  of  the  figure. 


employed  is  as  follows:  The  frog's  muscles'are  most  convenient  for  ex- 
periment, and  a  muscle  of  regular  shape,  in  which  the  fibres  are  parallel, 
is  selected.  The  ends  are  cut  off  by  clean  vertical  cuts,  and  the  resulting 
piece  of  muscle  is  called  a  regular  muscle  prism.  The  muscle  prism  is  in- 
sulated, and  a  pair  of  non-polarizable  electrodes  connected  with  a  very  deli- 
cate galvanometer  are  applied  to  various  points  of  the  prism,  and  by  a  de- 
flection of  the  needle  to  a  greater  or  less  extent  in  one  direction  or  another, 
the  strength  and  direction  of  the  currents  in  the  piece  of  muscle  can  be 
estimated.  It  is  necessary  to  use  non-polarizable  and  not  metallic  elec- 
trodes in  this  experiment,  as  otherwise  there  is  no  certainty  that  the  whole 
of  tlie  current  observed  is  communicated  from  the  muscle  and  is  not 
derived  from  tlie  metallic  electrodes  tliemselves  in  consequence  of  the 
action  of  the  saline  juices  of  the  tissues  upon  them.  The  form  of  the 
non-polarizable  electrodes  is  a  inodifunition  of  Du  Bois  Heymond^s  appa- 


CAUSES  AND  PHENOMENA  OF  MOTION, 


23 


ratus  (Fig.  275),  which  consists  of  a  somewhat  flattened  glass  cylinder  a, 
drawn  abruptly  to  a  point  and  fitted  to  a  socket  capable  of  movement  and 
attached  to  a  stand  A,  so  that  it  can  be  raised  or  lowered  as  required.  The 
lower  portion  of  the  cylinder  is  filled  with  china  clay  moistened  with 
saline  solution,  part  of  which  projects  through  its  drawn-out  point,  the 
rest  of  the  cylinder  is  fitted  with  a  saturated  solution  of  zinc  sulphate 
into  which  dips  a  well  amalgamated  piece  of  zinc  which  is  connected  by 
means  of  a  wire  with  the  galvanometer.  In  this  way  the  zinc  sulphate 
forms  an  homogeneous  and  non-polar izable  conductor  between  the  zinc 
and  the  china  clay.  A  second  electrode  of  the  same  kind  is,  of  course, 
necessary. 

In  such  a  regular  muscle  prism  the  currents  are  found  to  be  as 
follows: — 


If  from  a  point  on  the  surface  a  line — the  equator — be  drawn  across 
the  muscle  prism  equally  dividing  it,  currents  pass  from  this  point  to 
points  away  from  it,  which  are  weak  if  the  points  are  near,  and  increase 
in  strength  as  the  points  are  further  and  further  away  from  the  equator; 
the  strongest  passing  from  the  equator  to  a  point  representing  the  middle 
of  the  cut  ends  (Fig.  276,  2);  currents  also  pass  from  points  nearer  the 
equator  to  those  more  remote  (Fig.  276,  1,  3,  4),  but  not  from  points 
equally  distant,  or  iso-electric  points  (Fig.  276,  6.  7,  8).  The  cut  ends 
are  always  negative  to  the  equator.  These  currents  are  constant  for  some 
time  after  removal  of  the  muscle  from  the  body,  and  in  fact  remain  as 
long  as  the  muscle  retains  its  life.  They  are  in  all  probability  due  to 
chemical  change  going  on  in  the  muscles. 

The  currents  are  diminished  by  fatigue  and  are  increased  by  an  in- 
crease of  temperature  within  natural  limits.  If  the  uninjured  tendon  be 
used  as  the  end  of  the  muscle,  and  the  muscle  be  examined  without  re- 
moval from  the  body,  the  currents  are  very  feeble,  but  they  are  at  once 
much  increased  by  injuring  the  muscle,  as  by  cutting  otf  its  tendon.  The 
last  observation  appears  to  show  that  they  are  right  who  believe  that  the 
currents  do  not  exist  in  muscles  uninjured  in  situ,  but  that  injury,  either 


Fig.  276. — Diagram  of  the  currents  in  a  muscle  prism.   (Du  Bois  Reymond.) 


24 


HAND-BOOK  OF  PHYSIOLOGY 


mechanical,  chemical  or  tliermal,  will  render  the  injured  part  electrically 
negative  to  other  points  on  the  muscle.  In  a  frog^s  heart  it  has  been 
shown,  too,  that  no  currents  exist  during  its  inactivity,  but  that  as  soon 
as  it  is  injured  in  any  way  currents  are  developed,  the  injured  part  being 
negative  to  the  rest  of  the  muscle.  The  currents  which  have  been  above 
described  are  called  either  natural  muscle  currents  or  currents  of  rest, 
according  as  they  are  looked  upon  as  always  existing  in  muscle  or  as 
developed  when  a  part  of  the  muscle  is  subjected  to  injury;  in  either 
case,  up  to  a  certain  point,  it  is  agreed  that  the  strength  of  the  currents 
is  in  direct  proportion  to  the  injury. 

II.  Activity. 

The  property  of  muscular  tissue,  by  which  its  peculiar  functions  are 
exercised,  is  its  contractility,  which  is  excited  by  all  kinds  of  stimuli 
applied  either  directly  to  the  muscles,  or  indirectly  to  them  through  the 
medium  of  their  motor  nerves.  This  property,  although  commonly 
brought  into  action  through  the  nervous  system,  is  inherent  in  the  mus- 
cular tissue.  For — (1).  it  may  be  manifested  in  a  muscle  which  is  iso- 
lated from  the  influence  of  the  nervous  system  by  division  of  the  nerves 
supplying  it,  so  long  as  the  natural  tissue  of  the  muscle  is  duly  nourished; 
and  (2).  it  is  manifest  in  a  portion  of  muscular  fibre,  in  which,  under 
the  microscope,  no  nerve-fibre  can  be  traced.  (3).  Substances  such  as 
urari,  which  paralyze  the  nerve-endings  in  muscles,  do  not  at  all  diminish 
the  irritability  of  the  muscle.  (4).  When  a  muscle  is  fatigued,  a  local 
stimulation  is  followed  by  a  contraction  of  a  small  part  of  the  fibre  in  the 
immediate  vicinity  without  any  regard  to  the  distribution  of  nerve -fibres. 

If  the  removal  of  nervous  influence  be  long  continued,  as  by  division 
of  the  nerves  supplying  a  muscle,  or  in  cases  of  paralysis  of  long-standing, 
tlie  irritability,  i.e.,  the  power  of  both  perceiving  and  responding  to  a 
stimulus,  may  be  lost;  but  probably  this  is  chiefiy  due  to  the  impaired 
nutrition  of  the  muscular  tissue,  Avhich  ensues  through  its  inaction.  The 
irritability  of  muscles  is  also  of  course  soon  lost,  unless  a  supply  of  arterial 
blood  to  them  is  kept  up.  Thus,  after  ligature  of  the  main  arterial  trunk 
of  a  limb,  the  power  of  moving  the  muscles  is  partially  or  wholly  lost,  until 
the  collateral  circulation  is  established;  and  when,  in  animals,  the  abdom- 
inal aorta  is  tied,  the  hind  legs  are  rendered  almost  powerless. 

The  same  fact  may  be  readily  shown  by  compressing  the  abdominal 
aorta  in  a  rabbit  for  about  10  minutes;  if  the  pressure  be  released  and  tlie 
animal  be  placed  on  the  ground,  it  will  work  itself  along  with  its  front 
legs,  while  the  hind  legs  sprawl  helplessly  behind.  Gradually  the  muscles 
recover  their  power  and  become  quite  as  efficient  as  before. 

8o.  also,  it  is  to  the  imporfc(^t  supply  of  arterial  bUHnl  to  the  muscular 


CAUSES  AND  PHENOMENA  OF  MOTION. 


25 


tissue  of  the  heart,  that  the  cessation  of  the  action  of  this  organ  in 
asphyxia  is  in  some  measure  due. 

Sensibility. — Besides  the  property  of  contractility,  the  muscles, 
especially  the  striated,  possess  sensibility  by  means  of  the  sensory  nerve- 
fibres  distributed  to  them.  The  amount  of  common  sensibility  in  muscles 
is  not  great;  for  they  may  be  cut  or  pricked  without  giving  rise  to  severe 
pain,  at  least  in  their  healthy  condition.  But  they  have  a  peculiar  sensi- 
bility, or  at  least  a  peculiar  modification  of  common  sensibility,  which  is 
shown  in  that  their  nerves  can  communicate  to  the  mind  an  accurate 
knowledge  of  their  states  and  positions  when  in  action.  By  this  sensibil- 
ity, we  are  not  only  made  conscious  of  the  morbid  sensations  of  fatigue 
and  cramp  in  muscles,  but  acquire,  through  muscular  action,  a  knowledge 
of  the  distance  of  bodies  and  their  relation  to  each  other,  and  are  enabled 
to  estimate  and  compare  their  weight  and  resistance  by  the  effort  of  which 
we  are  conscious  in  measuring,  moving,  or  raising  them.  Except  with 
such  knowledge  of  the  position  and  state  of  each  muscle,  we  could  not 
tell  how  or  when  to  move  it  for  any  required  action;  nor  without  such  a 
sensation  of  effort  could  we  maintain  the  muscles  in  contraction  for  any 
prolonged  exertion. 

Muscular  Contraction. 

The  power  which  muscles  possess  of  contraction  may  be  called  forth 
by  stimuli  of  various  kinds,  viz.,  by  Mechanical,  Thermal,  Chemical,  and 
Electrical  means,  and  these  stimuli  may  also  be  a^^plied  directly  to  the 
muscle  or  indirectly  to  the  nerve  supplying  it.  There  are  distinct  advan- 
tages, however,  in  applying  the  stimulus  through  the  nerves,  as  it  is  more 
convenient,  as  well  as  more  potent. 

Mechanical  stimuli,  as  by  a  blow,  pinch,  prick  of  the  muscle  or  its 
nerve,  will  produce  a  contraction,  repeated  on  the  repetition  of  the  stim- 
ulus; but  if  applied  to  the  same  point  for  a  limited  number  of  times 
only,  as  such  stimuli  will  soon  destroy  the  irritability  of  the  preparation. 

Thermal  stimuli. — If  a  needle  be  heated  and  applied  to  a  muscle  or 
its  nerve,  the  muscle  will  contract.  A  temperature  of  over  100^  F. 
(37*8^  C.)  will  cause  the  muscles  of  a  frog  to  pass  into  a  condition  known 
as  heat  rigor. 

Chemical  stimuli. — A  great  variety  of  chemical  substances  will  excite 
the  contraction  of  muscles,  some  substances  being  more  potent  in  irrita- 
ting the  muscle  itself,  and  other  substances  having  more  effect  upon  the 
nerve.  Of  the  former  may  be  mentioned,  dilute  acids,  salts  of  certain 
metals,  e.g.,  zinc,  copper  and  iron;  to  the  latter  belong  strong  glycerin, 
strong  acids,  ammonia  and  bile  salts  in  strong  solution. 

Electrical  sti^yiuli. — These  are  most  frequently  used  as  muscle  stimuli, 
as  the  strength  of  the  stimulus  may  be  more  conveniently  regulated. 


26 


HAND-BOOK  OF  PHYSIOLOGY. 


The  kind  of  current  employed  may  be,  for  the  sake  of  clearness,  treated 
of  under  two  heads: — (1)  The  continuous  current,  and  (2)  Tlie  induced 
current.  (1)  The  continuous  current  is  supplied  by  a  battery  such  as 
that  of  Daniell,  by  which  an  electrical  current  which  varies  but  little  in 
intensity  is  obtained.  The  battery  (Fig.  2TT)  consists  of  a  positive  plate  of 
well-amalgamated  zinc  immersed  in  a  porous  cell,  containing  dilute  sul- 
phuric acid;  and  this  cell  is  again  contained  within  a  larger  copper  vessel 
(forming  the  negative  plate),  containing  besides  a  saturated  solution  of 
copper  sulphate.  The  electrical  current  is  made  continuous  by  the  use  of 
the  two  fluids  in  the  following  manner.  The  action  of  the  dilute  sulphui'ic 
acid  upon  the  zinc  plate  partly  dissolves  it  and  liberates  hydrogen,  and 
this  gas  passes  through  the  porous  vessel  and  decomposes  the  copper  sul- 
phate into  copper  and  sulphuric  acid.    The  former  is  deposited  upon  the 


Fig.  277.— Diagram  of  a  Darnell's  Battery.   (After  Balfour  Stewart.) 

copper  plate  and  the  latter  passes  through  the  porous  vessel  to  renew  the 
sulphuric  acid  which  is  being  used  up.  The  copper  sulphate  solution  is 
renewed  by  spare  crystals  of  the  salt  which  are  kept  on  a  little  shelf 
attached  to  the  copper  plate  and  slightly  below  the  level  of  the  solution 
in  the  vessel.  The  current  of  electricity  supplied  by  this  battery  will 
continue  without  variation  for  a  considerable  time.  Other  continuous- 
current  batteries  such  as  Grove's  may  be  used  in  place  of  DanielFs.  The 
way  in  which  the  apparatus  is  arranged  is  to  attach  wires  to  the  copper 
and  zinc  plates  and  to  bring  them  to  a  key,  which  is  a  little  apparatus 
for  connecting  the  wires  of  a  battery.  One  often  employed  is  Du  Bois 
Reymond's  (Fig.  280,  d);  it  consists  of  two  pieces  of  brass  about  an  inch 
long,  in  each  of  which  are  two  holes  for  wires  and  binding  screws  to  fix 
them  tightly;  these  pieces  of  brass  are  fixed  upon  a  vulcanite  plate,  to 
the  under  surface  of  which  is  a  screw  clamp  by  which  it  can  be  secured 
to  the  table.  The  interval  between  the  pieces  of  brass  can  be  bridged 
over  by  means  of  a  third  thinner  piece  of  similar  metal  fixed  by  a  screw 
to  one  of  the  brass  pieces  and  capable  of  movement  by  a  handle  at  right 
angles,  so  as  to  touch  the  other  piece  of  brass.    If  the  wires  from  the 


CAUSES  AND  PHENOMEI^A  OF  MOTION. 


27 


battery  are  brought  to  the  inner  binding  screws,  and  the  bridge  be  brought 
to  connect  them,  the  current  passes  across  it  and  back  to  the  battery. 
Wires  are  connected  with  the  outer  binding  screws,  and  the  other  ends 
are  approximated  for  about  two  inches,  but,  being  covered  except  at  their 
points,  are  insulated,  the  uncovered  points  are  about  an  eighth  of  an  inch 
apart.  These  wires  are  the  electrodes,  and  the  electrical  stimulus  is  ap- 
plied to  the  muscle,  if  they  are  placed  behind  its  nerve  and  the  connection 
between  the  two  brass  plates  of  the  key  be  broken  by  depressing  the 
handle  of  the  bridge  and  so  raising  the  connecting  piece  of  metal.  The 
key  is  then  said  to  be  opened.  (2)  The  induced  current, — An  induced 
current  is  developed  by  means  of  an  apparatus  called  an  induction  coil, 
and  the  one  employed  for  physiological  purposes  is  mostly  the  one  (Fig. 
278). 

Wires  from  a  battery  are  brought  to  the  two  binding  screws  d'  and  d, 


Fig.  278.— Du  Bois  Reymond's  induction  coil. 


a  key  intervening.  These  binding  screws  are  the  ends  of  a  coil  of  coarse 
covered  wire  called  the  primary  coil.  The  ends  of  a  coil  of  finer  cov- 
ered wire  g,  are  attached  to  two  binding  screws  to  the  left  of  the  figure, 
one  only  of  which  is  visible.  This  is  the  secondary  coil  and  is  capable  of 
being  moved  nearer  to  c  along  a  grooved  and  graduated  scale.  To  the 
binding  screws  to  the  left  of  g,  the  wires  of  electrodes  used  to  stimulate 
the  muscle  are  attached.  If  the  key  in  the  circuit  of  wires  from  the  bat- 
tery to  the  primary  coil  (primary  circuit)  be  closed,  the  current  from  the 
battery  passes  through  the  primary  coil  and  across  the  key  to  the  battery 
and  continues  to  pass  as  long  as  the  key  continues  closed.  At  the  moment 
of  closure  of  the  key,  at  the  exact  instant  of  the  completion  of  the  primary 
circuit,  an  instantaneous  current  of  electricity  is  induced  in  the  secondary 
coil,  g,  if  it  be  sufficiently  near,  and  the  nearer  it  is  to  c,  the  stronger  is 
the  current.    The  induced  current  is  only  momentary  in  duration  and 


28 


HAND-BOOK  OF  PHYSIOLOGY. 


does  not  continue  during  the  whole  of  the  period  when  the  primary  cir- 
cuit is  complete.  When,  however,  the  primary  current  is  broken  bv 
opening  the  key,  a  second,  also  momentary,  current  is  induced  in  g.  The 
former  induced  current  is  called  the  making,  and  the  latter  the  breaking 
shock;  the  former  is  in  the  opposite  to,  and  the  latter  in  the  same  direc- 
tion, as  the  primary  current. 

The  induction  coil  may  be  used  to  produce  a  rapid  series  of  shocks  by 
means  of  another  and  accessory  part  of  the  apparatus  at  the  right  of  the 
figure.  If  the  wires  from  a  battery  are  connected  with  the  two  pillars  by 
the  binding  screws,  one  below  c,  and  the  other,  a,  the  course  of  the  cur- 
rent is  indicated  in  Fig.  279,  the  direction  being  indicated  by  the  arrows. 


Fig.  279.— Diagram  of  the  course  of  the  current  in  the  magnetic  interrupter  of  Du  Bois  Reymond's 
induction  coil.   (Hehnholz's  modification.) 

The  current  passes  up  the  pillar  from  e  and  along  the  spring,  if  the  end  of  d' 
be  close  to  the  spring,  and  the  current  passes  to  the  primary  coil  c,  and 
to  wires  covering  two  upright  pillars  of  soft  iron,  from  them  to  the  j^illar 
a,  and  out  by  the  wires  to  the  battery;  in  passing  along  the  wire,  Z*,  the 
soft  iron  is  converted  into  a  magnet  and  so  attracts  the  hammer,  /,  of  the 
spring,  breaks  the  connection  of  the  spring  with  and  so  cuts  off  the 
current  from  the  primary  coil  and  also  from  the  electro-magnet.  As  the 
pillars,  hf  are  no  longer  magnetized  the  spring  is  released  and  the  current 
passes  in  the  first  direction,  and  is  in  like  manner  interrupted.  At  each 
make  and  break  of  the  primary  current,  currents  corresponding  are  in- 
duced in  the  secondary  coil.  These  currents  are,  as  before,  in  an  opposite 
direction,  but  are  not  equal  in  intensity,  the  break  shock  being  greater. 
In  order  that  the  shocks  should  be  about  equal  at  the  make  and  break,  a 
wire  (Fig.  279,  e')  connects  e  and  d',  and  the  screw  d'  is  raised  out  of  reach  of 
the  spring,  and  d  is  raised  (as  in  Fig.  279),  so  tliat  part  of  the  current 
always  passes  through  tlie  primary  coil  and  electro-magnet.  When  the 
spring  touolies  d,  tlie  current  in  h  is  diminished,  but  never  entirely  with- 
drawn, and  the  primary  current  is  altered  in  intensity  at  each  contact  of 
the  spring  with  dy  but  never  entirely  broken. 


CAUSES  AND  PHENOMENA  OF  MOTION. 


29 


Record  of  Muscular  Contraction  under  Stimuli. 

The  muscles  of  the  frog  are  those  which  can  most  conveniently  be 
experimented  with  and  their  contractions  recorded.  The  frog  is  pithed, 
that  is  to  say  its  central  nervous  system  is  entirely  destroyed  by  the  inser- 
tion of  a  stout  needle  into  the  spinal  cord  and  the  parts  above  it.  One  of 
its  lower  extremities  is  used  in  the  following  manner.  The  large  trunk  of 
the  sciatic  nerve  is  dissected  out  at  the  back  of  the  thigh,  and  a  pair  of 
electrodes  is  inserted  behind  it.    The  tendo-achillis  is  divided  from  its 


Fig.  280.— Arrangement  of  the  apparatus  necessary  for  recording  muscle  contractions  with  a 
revolving  cylinder  carrying  smoked  paper.  A.  revolving  cylinder;  B,  the  frog  arranged  upon  a  cork- 
covered  board  which  is  capable  of  being  raised  or  lowered  on  the  upright,  which  also  can  be  moved 
along  a  solid  triangular  bar  of  metal  attached  to  the  base  of  the  recording  apparatus— the  tendon  of 
the  gastrocnemius  is  attached  to  the  writing  lever  properly  weighted  by  a  ligature.  The  electrodes 
from  the  secondary  coil  pass  to  the  apparatus— being,  for  the  sake  of  convenience,  first  of  all  brought 
to  a  key,  D  (Du  Bois  Raymond's);  C,  the  induction  coil;  F,  the  battery  (in  this  figure  a  bichromate 
one);  E,  the  key  (Morse's)  in  the  primary  circuit. 

attachment  to  the  os  calcis,  and  a  ligature  is  tightly  tied  round  it.  This 
tendon  is  part  of  the  broad  muscle  of  the  thigh  (gastrocnemius)  which 
arises  from  above  the  condyles  of  the  femur.  The  femur  is  now  fixed 
to  a  board  covered  with  cork,  and  the  ligature  attached  to  the  tendon  is 
tied  to  the  upright  of  a  piece  of  metal  bent  at  right  angles  (Fig.  280,  b), 
which  is  capable  of  movement  about  a  pivot  at  its  knee,  the  horizontal 
portion  carrying  a  writing  lever  (myograph).  When  the  muscle  con- 
tracts the  lever  is  raised.    It  is  necessary  to  attach  a  small  weight  to  the 


30  HAND-BOOK  OF  PHYSIOLOGY. 

lever.  In  this  arrangement  the  muscle  is  i7i  situ,  and  the  nerve  disturbed 
from  its  relations  as  little  as  possible. 

The  muscle  may,  however,  be  detached  from  the  body  with  the  lower 
end  of  the  femur  from  which  it  arises,  and  the  nerve  going  to  it  may  be 
taken  away  with  it.  The  femur  is  divided  at  about  the  lower  third.  The 
bone  is  held  in  a  firm  clamp,  the  nerve  is  placed  upon  two  electrodes  con- 
nected with  an  induction  apparatus,  and  the  lower  end  of  the  muscle  is 
connected  by  means  of  a  ligature  attached  to  its  tendon  with  a  lever 
which  can  write  on  a  recording  apparatus. 

To  prevent  evaporation  this  so-called  nerve-muscle  preparation  is  placed 
under  a  glass  shade,  the  air  in  which  is  kept  moist  by  means  of  blotting 
paper  saturated  with  saline  solution. 

Effect  of  a  single  Induction  Shock. 

Taking  the  nerve-muscle  preparation  in  either  of  these  ways,  on 
closing  or  opening  the  key  in  the  primary  circuit  w^e  obtain  and  can 
record  a  contraction,  and  if  we  use  the  clockwork  apparatus  revolving 
rapidly,'  a  curve  is  traced  such  as  is  shown  in  (Fig.  281). 

Another  way  of  recording  the  contraction  is  by  the  pendulum  myo- 
graph (Fig.  282).    Here  the  movement  of  the  pendulum  along  a  certain 


Fig.  281.— Muscle-curve  obtained  by  the  pendulum  myograph,  s,  indicates  the  exact  instant  of 
the  induction  shock;  c,  commencement;  and m  a;,  the  maximum  elevation  of  lever;  /,  the  line  of  a 
vibrating  timing-fork.    (M.  Foster.) 

arc  is  substituted  for  the  clockwork  movement  of  the  other  apparatus. 
The  pendulum  carries  a  smoked  glass  plate  upon  which  tlie  writing  lever 
of  a  myograph  is  made  to  mark.  The  opening  or  breaking  shock  is  sent 
into  the  nerve-muscle  preparation  by  the  pendulum  in  its  swing  opening  a 
key  (Fig.  282,  C.)  in  tlic  primary  circuit. 

Single  Muscle  Contraction. — The  tracings  obtained  in  a  manner 
above  described  and  seen  in  Fig.  281,  may  be  thus  explained. 

The  upper  line  {m)  ro})resents  tlie  curve  traced  by  the  end  of  the  lever 


CAUSES  AND  PHENOMENA  OF  MOTION. 


31 


after  stimulation  of  the  muscle  by  a  single  induction-shock:  the  middle 
line  (/)  is  that  described  by  the  marking-lever,  and  indicates  by  a  sudden 
drop  the  exact  instant  at  which  the  induction-shock  was  given.  The 


Fig.  282.— Simple  form  of  pendulum  myograph  and  accessory  parts.  A,  pivot  upon  which  pendu- 
lum swings;  B,  catch  on  lower  end  of  myograph  opening  the  key,  C,  in  its  swing:  D,  a  spring-catch 
which  retains  myograph,  as  indicated  by  dotted  lines,  and  on  pressing  down  the  handle  of  which  the 
pendulum  swings  along  the  arc  to  D  on  the  left  of  figure,  and  is  caught  by  its  spring. 

lower  wavy  line  (t)  is  traced  by  a  vibrating  tuning-fork,  and  serves  to 
measure  precisely  the  intervals  of  time  occupied  in  each  part  of  the  con- 
traction. 


Fig.  283.— Tracing  of  a  double  muscle-curve.  To  be  read  from  left  to  right.  While  the  muscle 
was  engaged  in  the  first  contraction  (whose  complete  course,  had  nothing  intervened,  is  indicated  by 
the  dotted  line),  a  second  induction -shock  was  thrown  in,  at  such  a  time  that  the  second  contraction 
began  just  as  the  first  was  beginning  to  decline.  The  second  curve  is  seen  to  stai't  from  the  first,  as 
does  the  first  from  the  base  fine.   (M.  Foster.) 

It  will  be  observed  that  after  the  stimulus  has  been  applied,  as  indi- 
cated by  the  vertical  line  s,  there  is  an  interval  before  the  contraction 


32  HAND-BOOK  OF  PHYSIOLOGY. 

commences,  as  indicated  by  the  line  c.  This  interval,  termed  the  ^ ^latent 
period'^  (Helmholtz),  when  measured  by  the  number  of  vibrations  of  the 
tuning-fork  between  the  lines  s  and  c,  is  found  to  be  about  -^ho  sec. 

Tlie  contraction  progresses  rapidly  at  first  and  afterward  more  slowly  to 
the  maximum  (the  point  in  the  curve  through  which  the  line  mx  is  drawn) 
which  takes  yfo-  sec,  and  then  the  muscle  elongates  again  as  indicated  by 
the  descending  curve,  at  first  rapidly,  afterward  more  slowly,  till  it  attains 
its  original  length  at  the  point  indicated  by  the  line  c',  occupying  y|-g-  sec. 

The  muscle  curve  obtained  from  the  heart  resembles  that  of  unstriped 
muscles  in  the  Jong  duration  of  the  effect  of  stimulation;  the  descending 
curve  is  very  much  prolonged. 

The  greater  part  of  the  latent  period  is  taken  up  by  changes  in  the 
muscle  itself,  the  rest  being  occupied  in  the  propagation  of  the  shock 
along  the  nerve  (M.  Foster). 

Tetanus. — If  instead  of  a  single  induction-shock  through  the  prepa- 
ration we  pass  two,  one  immediately  after  the  other,  when  the  point  of 


Fig.  284.~Curve  of  tetanus,  obtained  from  the  gastrocnemius  of  a  frog,  where  the  shocks  were 
sent  in  from  an  induction  coil,  about  sixteen  times  a  second,  by  the  interruption  of  the  primary  cur- 
rent by  means  of  a  vibrating  spring,  which  dipped  into  a  cnp  of  mercury,  and  broke  the  primary 
current  at  each  vibration. 

stimulation  of  the  second  one  corresponds  to  the  maximum  of  the  first, 
a  second  curve  (Fig.  283)  will  occur  which  will  commence  at  the  highest 
point  of  the  first  and  will  rise  as  high,  so  that  the  sum  of  the  height  of 


Fig.  285.— Curve  of  tebanus,  from  a  series  of  very  rapid  shocks  from  a  magnetic  interrupter. 

the  two  exactly  equals  twice  the  height  of  the  first.  If  a  third  and  a  fourth 
shock  be  iiassed,  a  similar  effect  will  ensue,  and  curves  one  above  the  other 


CAUSES  AND  PHENOMENA  OF  MOTION. 


33 


will  be  traced,  the  third  being  slightly  less  than  the  second,  and  the 
fourth  than  the  third.  If  the  shocks  be  repeated  at  short  intervals,  how- 
ever, the  lever  after  a  time  ceases  to  rise  any  further,  and  the  contraction 
which  has  reached  its  maximum  is  maintained  (Fig.  285),  and  the  lever 
marks  a  straight  line  on  the  recording  cylinder.  This  condition  is  called 
tetanus  of  muscle.  The  condition  of  "an  ordinary  tetanic  muscular 
movement  is  essentially  a  vibratory  movement,  the  apparently  rigid  and 
firm  muscular  mass  is  really  the  subject  of  a  whole  series  of  vibrations,  a  se- 
ries namely  of  simple  spasms;  it  will  be  readily  understood  why  a  tetanized 
muscle,  like  all  other  vibrating  bodies,  gives  out  a  sound'^  (M.  Foster). 

If  the  stimuli  are  not  quite  so-  rapidly  sent  in  the  line  of  maximum 
contraction  it  becomes  somewhat  wavy,  indicating  a  slight  tendency  of  the 
muscles  to  relax  during  the  intervals  between  the  stimuli  (Fig.  284). 

Muscular  Work. — We  have  seen  (p.  124,  Vol.  I.)  that  ivorh  is  esti- 
mated by  multiplying  the  weight  raised,  by  the  height  through  which  it 
has  been  lifted.  It  has  been  found  that  in  order  to  obtain  the  maximum 
of  work,  a  muscle  must  be  moderately  loaded :  if  the  weight  be  increased 
beyond  a  certain  point,  the  muscle  becomes  strained  and  raises  the  weight 
through  so  small  a  distance  that  less  work  is  accomplished.  If  the  load  is 
still  further  increased  the  muscle  is  completely  overtaxed,  cannot  raise  the 
weight,  and  consequently  does  no  work  at  all.  Practical  illustrations  of 
these  facts  must  be  familiar  to  every  one. 

The  power  of  a  muscle  is  usually  measured  by  the  maximum  weight 
which  it  will  support  without  stretching.  In  man  this  is  readily  deter- 
mined by  weighting  the  body  to  such  an  extent  that  it  can  no  longer  be 
raised  on  tiptoe:  thus  the  power  of  the  calf -muscles  is  determined 
(Weber). 

The  power  of  a  muscle  thus  estimated  depends  of  course  upon  its  cross- 
section.  The  power  of  a  human  muscle  is  from  two  to  three  times  as 
great  as  a  frog's  muscle  of  the  same  sectional  area. 

Fatigue  of  Muscle. — A  muscle  becomes  rapidly  exhausted  from 
repeated  stimulation,  and  the  more  rapidly,  the  more  quickly  the  induc- 
tion-shocks succeed  each  other. 

This  is  indicated  by  the  diminished  height  of  contraction  in  the  ac- 
companying diagrams  (Fig.  286).  It  will  be  seen  that  the  vertical  lines, 
which  indicate  the  extent  of  the  muscular  contraction,  decrease  in  length 
from  left  to  right.  The  line  A  B  drawn  along  the  tops  of  these  lines  i& 
termed  the  "fatigue  curve.''    It  is  usually  a  straight  line. 

In  the  first  diagram  the  effects  of  a  short  rest  are  shown :  there  is  a 
pause  of  three  minutes,  and  when  the  muscle  is  again  stimulated  it  con- 
tracts up  to  a',  but  the  recovery  is  only  temporary,  and  the  fatigue  curve, 
after  a  few  more  contractions,  becomes  continuous  with  that  before  the 
rest. 

In  the  second  diagram  is  represented  the  effect  of  a  stream  of  oxygenated 
Vol.  II.-3. 


34 


HAND-BOOK  OF  PHYSIOLOGY. 


blood.  Here  we  have  a  sudden  restoration  of  energy:  the  muscle  in  this 
case  makes  an  entirely  fresh  start  from  a,  and  the  new  fatigue  curve  is 
parallel  to,  and  never  coincides  with  the  old  one. 

A  fatigued  muscle  has  a  much  longer  ''latent  period"  than  a  fresh  one. 
The  slowness  with  which  muscles  respond  to  the  will  when  fatigued  must 
be  familiar  to  every  one. 

In  a  muscle  which  is  exhausted,  stimulation  only  causes  a  contraction 
producing  a  local  bulging  near  the  point  irritated.    A  similar  effect  may 


Fig.  286.— Fatigue  muscle-curves.  (Ray  Laukester.) 


be  produced  in  a  fresh  muscle  by  a  sharp  blow,  as  in  striking  the  biceps 
smartly  with  the  edge  of  the  hand,  when  a  hard  muscular  swelling  is  in- 
stantly formed. 

Accompaniments  of  Muscular  Contraction.— (1.)  Heat  is  de- 
veloped in  the  contraction  of  muscles.  Becquerel  and  Breschet  found, 
with  the  thertno-multiplier,  about  1°  Fahr.  of  heat  produced  by  each  forci- 
ble contraction  of  a  man's  biceps;  and  when  the  actions  were  long  con- 
tinued, the  temperature  of  the  muscle  increased  2°.  This  estimate  is 
probably  high,  as  in  the  frog's  muscle  a  considerable  contraction  has  been 
found  to  produce  an  elevation  of  temperature  equal  on  an  average  to 
less  than  0.  It  is  not  known  whether  this  development  of  heat  is  due 
to  chemical  changes  ensuing  in  the  muscle,  or  to  the  friction  of  its  fibres 
vigorously  acting:  in  either  case,  Ave  may  refer  to  it  a  part  of  the  heat 
developed  in  active  exercise  (p.  310,  Vol.  I.). 

(2.)  Sound  is  said  to  be  produced  when  muscles  contract  forcibly,  as 
mentioned  above.  Wollaston  showed  that  this  sound  might  be  easily 
heard  by  placing  the  ti])  of  the  little  finger  in  the  ear,  and  then  making 
some  muscles  contract,  as  those  of  the  ball  of  the  thumb,  whose  sound 
may  be  conducted  to  the  ear  through  the  substance  of  the  hand  and  finger. 


CAUSES  AND  PHENOMENA  OF  MOTION. 


35 


A  low  shaking  or  rumbling  sound  is  heard,  the  height  and  loudness  of  the 
note  being  in  direct  proportion  to  the  force  and  quickness  of  the  muscular 
action,  and  to  the  number  of  fibres  that  act  together,  or,  as  it  were,  in 
time. 

(3.)  Changes  in  shape. — The  mode  of  contraction  in  the  transversely 
striated  muscular  tissue  has  been  much  disputed.  The  most  probable 
account  is,  that  the  contraction  is  effected  by  an  approximation  of  the 
constituent  parts  of  the  fibrils,  which,  at  the  instant  of  contraction,  without 
any  alteration  in  their  general  direction,  become  closer,  flatter,  and  wider; 
a  condition  which  is  rendered  evident  by  the  approximation  of  the  trans- 
verse striae  seen  on  the  surface  of  the  fasciculus,  and  by  its  increased 
breadth  and  thickness.  The  appearance  of  the  zigzag  lines  into  which  it 
was  supposed  the  fibres  are  thrown  in  contraction,  is  due  to  the  relaxation 
of  a  fibre  which  has  been  recently  contracted,  and  is  not  at  once  stretched 
again  by  some  antagonist  fibre,  or  whose  extremities  are  kept  close  to- 
gether by  the  contractions  of  other  fibres.  The  contraction  is  therefore 
a  simple,  and,  according  to  Ed.  Weber,  a  uniform,  simultaneous,  and 
steady  shortening  of  each  fibre  and  its  contents.  What  each  fibril  or 
fibre  loses  in  length,  it  gains  in  thickness:  the  contraction  is  a  change  of 
form,  not  of  size;  it  is,  therefore,  not  attended  with  any  diminution  in  bulk, 
from  condensation  of  the  tissue.  This  has  been  proved  for  entire  muscles, 
by  making  a  mass  of  muscle,  or  many  fibres  together,  contract  in  a  vessel 
full  of  water,  with  which  a  fine,  perpendicular,  graduated  tube  commu- 
nicates. Any  diminution  of  the  bulk  of  the  contracting  muscle  would 
be  attended  by  a  fall  of  fluid  in  the  tube;  but  when  the  experiment  is 
carefully  performed,  the  level  of  the  water  in  the  tube  remains  the  same, 
whether  the  muscle  be  contracted  or  not. 

In  thus  shortening,  muscles  appear  to  swell  up,  becoming  rounder,  more 
prominent,  harder,  and  apparently  tougher.  But  this  hardness  of  muscle 
in  the  state  of  contraction,  is  not  due  to  increased  firmness  or  condensa- 
tion of  the  muscular  tissue,  but  to  the  increased  tension  to  which  the 
fibres,  as  well  as  their  tendons  and  other  tissues,  are  subjected  from  the 
resistance  ordinarily  opposed  to  their  contraction.  When  no  resistance 
is  offered,  as  when  a  muscle  is  cut  off  from  its  tendon,  not  only  is  no 
hardness  perceived  during  contraction,  but  the  muscular  tissu-e  is  even 
softer,  more  extensile,  and  less  elastic  than  in  its  ordinary  uncontracted 
state. 

(4.)  Chemical  changes. — (a)  The  reaction  of  the  muscle  which  is  nor- 
mally alkaline  or  neutral  becomes  decidedly  acid,  from  the  development 
of  sarcolactic  acid,  {h)  The  muscle  gives  out  carbonic  acid  gas  and  takes 
up  oxygen,  the  amount  of  the  carbonic  acid  given  out  not  appearing  to  be 
entirely  dependent  upon  the  oxygen  taken  in,  and  so  doubtless  in  part 
arising  upon  some  other  source.  {c)  Certain  imperfectly  understood 
chemical  changes  occur,  in  all  probability  connected  with  {a)  and  {d). 


36 


HAND-BOOK  OF  PHYSIOLOGY. 


Glycogen  is  diminished,  and  muscle  sugar  (inosite)  appears;  the  extrac- 
tives are  increased. 

(5.)  Electrical  clianges. — When  a  muscle  contracts  the  natural  muscle 
current  or  currents  of  rest  undergo  a  distinct  diminution,  which  is  due  to 
the  appearance  in  the  actively  contracting  muscle  of  currents  in  an  op- 
posite direction  to  those  existing  in  the  muscle  at  rest.  This  causes  a 
temporary  deflection  of  the  needle  of  a  galvanometer  in  a  direction  oppo- 
site to  the  original  current,  and  is  called  by  some  the  negative  variation  of 
the  muscle  current,  and  by  others  a  current  of  action. 

Conditions  of  Contraction. — {a)  The  irritability  of  muscle  is  great- 
est at  a  certain  mean  temperature;  {!))  after  a  number  of  contractions  a 
muscle  gradually  becomes  exhausted;  {c)  the  activity  of  muscles  after  a 


Fig.  287. — Muscle-curves  from  the  gastrocnemius  of  a  frog,  illustrating  effects  of  alterations  in 

temperature. 

time  disappears  altogether  when  they  are  removed  from  the  body  or  the 
arteries  are  tied;  {d)  oxygen  is  used  up  in  muscular  contraction,  but  a 
muscle  will  act  for  a  time  in  vacuo  or  a  gas  which  contains  no  oxygen: 
in  this  case  it  is  of  course  using  up  the  oxygen  already  in  store 
(Hermann). 

Response  to  Stimuli. — The  two  kinds  of  fibres,  the  striped  and 
unstriped,  have  characteristic  ditferences  in  the  mode  in  which  they  act 
on  the  application  of  the  same  stimulus;  ditferences  which  may  be  ascribed 
in  great  part  to  their  respective  differences  of  structure,  but  to  some 
degree,  possibly,  to  their  respective  modes  of  connection  with  the  nervous 
system.  When  irritation  is  applied  directly  to  a  muscle  with  striated 
fibres,  or  to  the  motor  nerve  supplying  it,  contraction  of  the  part  irri- 
tated, and  of  that  only,  ensues;  and  this  contraction  is  instantaneous,  and 
ceases  on  the  instant  of  withdrawing  the  irritation.  But  when  any  part 
with  unstriped  muscular  fibres,  e.g.,  the  intestines  or  bladder,  is  irritated, 
the  subsequent  contraction  ensues  more  slowly,  extends  beyond  the  part 
irritated,  and,  with  alternating  relaxation,  continues  for  some  time  after 
the  withdrawal  of  the  irritation.  The  difference  in  the  modes  of  con- 
traction of  the  two  kinds  of  muscular  fibres  may  be  particularly  illus- 
trated by  the  effects  of  the  electro-magnetic  stimulus.  Hie  rapidly  suc- 
ceeding shocks  given  by  this  means  to  the  nerves  of  muscles  excite  in 
all  the  transversely-striated  muscles  a  fixed  state  of  tetanic  contraction  as 
previously  described,  which  lasts  as  long  as  the  stimulus  is  continued,  and 
on  its  withdrawal  instantly  ceases;  but  in  the  muscles  with  smooth  fibres 


CAUSES  AND  PHENOMENA  OF  MOTION. 


37 


they  excite,  if  any  movement,  only  one  that  ensues  slowly,  is  compara- 
tively slight,  alternates  with  rest,  and  continues  for  a  time  after  the 
stimulus  is  withdrawn. 

In  their  mode  of  responding  to  these  stimuli,  all  the  skeletal  muscles, 
or  those  with  transverse  striae,  are  alike;  but  among  those  with  plain  or 
unstriped  fibres  there  are  many  ditferences, — a  fact  which  tends  to  con- 
firm the  opinion  that  their  peculiarity  depends  as  well  on  their  connection 
with  nerves  and  ganglia  as  on  their  own  properties.  The  ureters  and 
gall-bladder  are  the  parts  least  excited  by  stimuli:  they  do  not  act  at  all 
till  the  stimulus  has  been  long  applied,  and  then  contract  feebly,  and  to  a 
small  extent.  The  contractions  of  the  caecum  and  stomach  are  quicker 
and  wider-spread:  still  quicker  those  of  the  iris,  and  of  the  urinary  blad- 
der if  it  be  not  too  full.  The  actions  of  the  small  and  large  intestines,  of 
the  vas  deferens,  and  pregnant  uterus,  are  yet  more  vivid,  more  regular, 
and  more  sustained;  and  they  require  no  more  stimulus  than  that  of  the 
air  to  excite  them.  The  heart,  on  account,  doubtless,  of  its  striated 
muscle,  is  the  quickest  and  most  vigorous  of  all  the  muscles  of  organic 
life  in  contracting  upon  irritation,  and  appears  in  this,  as  in  nearly  all 
other  respects,  to  be  the  connecting  member  of  the  two  classes  of  muscles. 

All  the  muscles  retain  their  property  of  contracting  under  the  influence 
of  stimuli  applied  to  them  or  to  their  nerves  for  some  time  after  death, 
the  period  being  longer  in  cold-blooded  than  in  warm-blooded  Verte- 
brata,  and  shorter  in  Birds  than  in  Mammalia.  It  would  seem  as  if  the 
more  active  the  respiratory  process  in  the  living  animal,  the  shorter  is  the 
time  of  duration  of  the  irritability  in  the  muscles  after  death;  and  this 
is  confirmed  by  the  comparison  of  different  species  in  the  same  order  of 
Vertebrata.  But  the  period  during  which  this  irritability  lasts,  is  not  the 
same  in  all  persons,  nor  in  all  the  muscles  of  the  same  persons.  In  a 
man  it  ceases,  according  to  Nysten,  in  the  following  order: — first  in  the 
left  ventricle,  then  in  the  intestines  and  stomach,  the  urinary  bladder, 
right  ventricle,  oesophagus,  iris;  then  in  the  voluntary  muscles  of  the 
trunk,  lower  and  upper  extremities;  lastly  in  the  right  and  left  auricle  of 
the  heart. 

III.  RiGOE  MOETIS. 

After  the  muscles  of  the  dead  body  have  lost  their  irritability  or  capa- 
bility of  being  excited  to  contraction  by  the  application  of  a  stimulus, 
they  spontaneously  pass  into  a  state  of  contraction,  apparently  identical 
with  that  which  ensues  during  life.  It  affects  all  the  muscles  of  the 
body;  and,  where  external  circumstances  do  not  prevent  it,  commonly 
fix^s  the  limbs  in  that  which  is  their  natural  posture  of  equilibrium  or 
rest.  Hence,  and  from  the  simultaneous  contraction  of  all  the  muscles 
of  the  trunk,  is  produced  a  general  stiffening  of  the  body,  constituting  the 
rigor  mortis  or  jjost-mortem  rigidity. 


38 


HAXD-BOOK  OF  PHYSIOLOGY. 


When  this  condition  has  set  in,  the  muscle  becomes  acid  in  reaction 
(due  to  sarco-lactic  acid),  and  gives  off  carbonic  acid  in  great  excess.  Its 
Yohime  is  slightly  diminished:  the  muscular  fibres  become  shortened 
and  opaque,  and  their  substance  has  set  firm.  It  comes  on  much  more 
rapidly  after  muscular  activity,  and  is  hastened  by  warmth.  It  may  be 
brought  on,  in  muscles  exposed  for  experiment,  by  the  action  of  distilled 
water  and  many  acids,  also  by  freezing  and  thawing  again. 

Cause. — The  immediate  cause  of  rigor  seems  coagulation  of  the 
muscle  plasma  (Briicke,  Kiihne,  Norris).  We  may  distinguish  three 
main  stages. — (1.)  Gradual  coagulation.  (2.)  Contraction  of  coagulated 
muscle-clot  (myosin)  and  squeezing  out  of  muscle-serum.  (3.)  Putrefac- 
tion. After  the  first  stage,  restoration  is  possible  through  the  circulation 
of  arterial  blood  through  the  muscles,  and  even  when  the  second  stage 
has  set  in,  vitality  may  be  restored  by  dissolving  the  coagulum  of  the 
muscle  in  salt  solution,  and  passing  arterial  blood  through  its  vessels. 
In  the  third  stage  recovery  is  impossible. 

Order  of  Occurrence. — The  muscles  are  not  affected  simultaneously 
by  post-mortem  contraction.  It  affects  the  neck  and  lower  jaw  first; 
next,  the  upper  extremities,  extending  from  above  downward;  and  lastly, 
reaches  the  lower  limbs;  in  some  rare  instances  only,  it  affects  the  lower 
extremities  before,  or  simultaneously  with,  the  upper  extremities.  It 
usually  ceases  in  the  order  in  which  it  began;  first  at  the  head,  then  in 
the  upper  extremities,  and  lastly  in  the  lower  extremities.  It  never  com- 
mences earlier  than  ten  minutes,  and  never  later  than  seven  hours,  after 
death;  and  its  duration  is  greater  in  proportion  to  the  lateness  of  its  ac- 
cession. Heat  is  developed  during  the  passage  of  a  muscular  fibre  into 
the  condition  of  rigor  mortis. 

Since  rigidity  does  not  ensue  until  muscles  have  lost  the  capacity  of 
being  excited  by  external  stimuli,  it  follows  that  all  circumstances  which 
cause  a  speedy  exhaustion  of  muscular  irritability,  induce  an  early  occur- 
rence of  the  rigidity,  while  conditions  by  which  the  disappearance  of  the 
irritability  is  delayed,  are  succeeded  by  a  tardy  onset  of  this  rigidity. 
Hence  its  speedy  occurrence,  and  equally  speedy  departure,  in  the  bodies 
of  persons  exhausted  by  chronic  diseases;  and  its  tardy  onset  and  long 
continuance  after  sudden  death  from  acute  diseases.  In  some  cases  of 
sudden  death  from  lightning,  violent  injuries,  or  paroxysms  of  passion, 
rigor  mortis  has  been  said  not  to  occur  at  all;  but  this  is  not  always 
the  case.  It  may,  indeed,  be  doubted  whether  there  is  really  a  complete 
absence  of  the  post-mortem  rigidity  in  any  such  cases;  for  the  experi- 
ments of  Brown-Sequard  make  it  probable  that  the  rigidity  may  super- 
vene immediately  after  death,  and  then  pass  away  with  such  rapidity  ^as 
to  be  scarcely  observable. 

Experiments. — Brown-Sequard  took  five  rabbits,  and  killed  them  by 


CAUSES  AND  PHENOMENA  OF  MOTION. 


39 


removing  their  hearts.  In  the  first,  rigidity  came  on  in  10  hOurs,  and 
lasted  192  hours;  in  the  second,  which  was  feebly  electrified,  it  com- 
menced in  7  hours,  and  lasted  144;  in  the  third,  which  was  more  strongly 
electrified,  it  came  on  in  two,  and  lasted  72  hours;  in  the  fourth,  which 
was  still  more  strongly  electrified,  it  came  on  in  one  hour,  and  lasted  20; 
while,  in  the  last  rabbit,  which  was  submitted  to  a  powerful  electro -gal- 
vanic current,  the  rigidity  ensued  in  seven  minutes  after  death,  and 
passed  away  in  25  minutes.  From  this  it  appears  that  the  more  powerful 
the  electric  current,  the  sooner  does  the  rigidity  ensue,  and  the  shorter  is 
its  duration;  and  as  the  lightning  shock  is  so  much  more  powerful  than 
any  ordinary  electric  discharge,  the  rigidity  may  ensue  so  early  after 
death,  and  pass  away  so  rapidly  as  to  escape  detection.  The  influence 
exercised  upon  the  onset  and  duration  of  post-mortem  rigidity  by  causes 
which  exhaust  the  irritability  of  the  muscles,  was  well  illustrated  in 
further  experiments  by  the  same  physiologist,  in  which  he  found  that  the 
rigor  mortis  ensued  far  more  rapidly,  and  lasted  for  a  shorter  period  in 
those  muscles  which  had  been  powerfully  electrified  just  before  death 
than  those  which  had  not  been  thus  acted  upon. 

The  occurrence  of  rigor  mortis  is  not  prevented  by  the  previous  exist- 
ence of  paralysis  in  a  part,  provided  the  paralysis  has  not  been  attended 
with  very  imperfect  nutrition  of  the  muscular  tissue. 

The  rigidity  affects  the  involuntary  as  well  as  the  voluntary  mugcles, 
whether  they  be  constructed  of  striped  or  unstriped  fibres.  The  rigidity 
of  involuntary  muscles  with  striped  fibres  is  shown  in  the  contraction  of 
the  heart  after  death.  The  contraction  of  the  muscles  with  unstriped 
fibres  is  shown  by  an  experiment  of  Valentin,  who  found  that  if  a  gradu- 
ated tube  connected  with  a  portion  of  intestine  taken  from  a  recently- 
killed  animal,  be  filled  with  water,  and  tied  at  the  opposite  end,  the  water 
will  in  a  few  hours  rise  to  a  considerable  height  in  the  tube,  owing  to  the 
contraction  of  the  intestinal  walls.  It  is  still  better  shown  in  the  arteries, 
of  which  all  that  have  muscular  coats  contract  after  death,  and  thus  pre- 
sent the  roundness  and  cord-like  feel  of  the  arteries  of  a  limb  lately 
removed,  or  tho^e  of  a  body  recently  dead.  Subsequently  they  relax,  as 
do  all  the  other  muscles,  and  feel  lax  and  flabby,  and  lie  as  if  flattened, 
and  with  their  walls  nearly  in  contact. 

Actions  of  the  Voluntaey  Muscles. 

The  greater  part  of  the  voluntary  muscles  of  the  body  act  as  sources 
of  power  for  removing  levers, — the  latter  consisting  of  the  various  bones 
to  which  the  muscles  are  attached. 

Examples  of  the  three  orders  of  levers  in  the  Human  Body. — All  levers 
have  been  divided  into  three  kinds,  according  to  the  relative  position  of 
the  poioer,  the  iceight  to  be  removed,  and  the  axis  of  motion  or  fulcrum. 
In  a  lever  of  the  first  kind  the  poiuer  is  at  one  extremity  of  the  lever,  the 
loeight  at  the  other,  and  the  fulcrum  between  the  two.    If  the  initial 


40 


HAND-BOOK  OF  PHYSIOLOGY. 


letters  only  of  thepoiuer,  weight,  and  fulcrum  be  used,  the  arrangement 
will  stand  thus: — I^.F.W.  A  poker,  as  ordinarily  used,  or  the  bar  in 
Fig.  288,  may  be  cited  as  an  example  of  this  variety  of  lever;  while,  as  an 
instance  in  which  the  bones  of  the  human  skeleton  are  used  as  a  lever  of 
the  same  kind,  may  be  mentioned  the  act  of  raising  the  body  from  the 
stooping  posture  by  means  of  the  hamstring  muscles  attached  to  the 
tuberosity  of  the  ischium  (Fig.  288). 


Fig.  5S8. 


In  a  lever  of  the  second  kind,  the  aiTangement  is  thus: — P.W.F. ;  and 
this  leverage  is  employed  in  the  act  of  raising  the  handles  of  a  wheel- 
barrow, or  in  stretching  an  elastic  band  as  in  Fig.  289.  In  the  human 
body  the  act  of  opening  the  mouth  by  depressing  the  lower  jaw  is  an 
example  of  the  same  kind, — the  tension  of  the  muscles  which  close  the 
jaw  representing  the  weight  (Fig.  289). 

In  a  lever  of  the  third  kind  the  arrangement  is — F.P.W.,  and  the 
act  of  raising  a  pole,  as  in  Fig.  290,  is  an  example.    In  the  human  body 


Fig.  289. 


there  are  numerous  examples  of  the  employment  of  this  kind  of  leverage. 
The  act  of  bending  the  fore-arm  may  be  mentioned  as  an  instance  (Fig. 
290).    The  act  of  biting  is  another  example. 

At  tlie  ankle  we  have  examples  of  all  three  kinds  of  lever.  1st  kind 
— Extending  tlie  foot.  3rd  kind — Flexing  tlie  foot.  In  both  these  cases 
the  foot  represents  the  weight:  the  ankle  joint  the  fulcrum,  the  power 
being  the  calf  muscles  in  the  first  case,  and  the  tibialis  anticus  in  the 


CAUSES  AND  PHENOMENA  OF  MOTION. 


41 


second  case.  2nd  kind — When  the  body  is  raised  on  tip-toe.  Here  the 
ground  is  the  fulcrum,  the  weight  of  the  body  acting  at  the  ankle  joint 
the  weight,  and  the  calf  muscles  the  power. 

In  the  human  body,  levers  are  most  frequently  used  at  a  disadvantage 
as  regards  power,  the  latter  being  sacrificed  for  the  sake  of  a  greater  range 
of  motion.    Thus  in  the  diagrams  of  the  first  and  third  kinds  it  is  evi- 


dent that  the  power .  is  so  close  to  the  fulcrum,  that  great  force  must  be 
exercised  in  order  to  produce  motion.  It  is  also  evident,  however,  from 
the  same  diagrams,  that  by  the  closeness  of  the  power  to  the  fulcrum  a 
great  range  of  movement  can  be  obtained  by  means  of  a  comparatively 
slight  shortening  of  the  muscular  fibres. 

The  greater  number  of  the  more  important  muscular  actions  of  the 
human  body — those,  namely,  which  are  arranged  harmoniously  so  as  to 
subserve  some  definite  purpose  or  other  in  the  animal  economy — are 
described  in  various  parts  of  this  work,  in  the  sections  which  treat  of  the 
physiology  of  the  processes  by  which  these  muscular  actions  are  resisted 
or  carried  out.  There  are,  however,  one  or  two  very  important  and  some- 
what complicated  muscular  acts  which  may  be  best  described  in  this  place. 

Walking. — In  the  act  of  walking,  almost  every  voluntary  muscle  in 
the  body  is  brought  into  play,  either  directly  for  purposes  of  progression, 
or  indirectly  for  the  proper  balancing  of  the  head  and  trunk.  The 
muscles  of  the  arms  are  least  concerned;  but  even  these  are  for  the  most 
part  instinctively  in  action  also  to  some  extent. 

Among  the  chief  muscles  engaged  directly  in  the  act  of  walking  are 
those  of  the  calf,  which,  by  pulling  up  the  heel,  pull  up  also  the  astraga- 
lus, and  with  it,  of  course,  the  whole  body,  the  weight  of  which  is  trans- 
mitted through  the  tibia  to  this  bone  (Fig.  291).  When  starting  to  walk, 
say  with  the  left  leg,  this  raising  of  the  body  is  not  left  entirely  to  the 
muscles  of  the  left  calf,  but  the  trunk  is  thrown  forward  in  such  a  way 
that  it  would  fall  prostrate  were  it  not  that  the  right  foot  is  brought  for- 
ward and  planted  on  the  ground  to  support  it.  Thus  the  muscles  of  the 
left  calf  are  assisted  in  their  action  by  those  muscles  on  the  front  of  the 
trunk  and  legs  which,  by  their  contraction,  pull  the  body  forward;  and, 
of  course,  if  the  trunk  form  a  slanting  line,  with  the  inclination  forward, 
it  is  plain  that  when  the  heel  is  raised  by  the  calf-muscles,  the  whole 
body  will  be  raised,  and  pushed  obliquely  forward  and  upward.  The 


Fig.  290. 


42 


HAND-BOOK  OF  PHYSIOLOGY. 


successive  acts  in  taking  the  first  step  in  walking  are  represented  in  Fig. 
291,  1,  2,  3. 

Now  it  is  evident  that  by  the  time  the  body  has  assumed  the  position 
No.  3,  it  is  time  that  the  right  leg  should  be  brought  forward  to  support 
it  and  prevent  it  from  falling  prostrate.  This  advance  of  the  other  leg 
(in  this  case  the  right)  is  effected  partly  by  its  mechanically  swinging  for- 
ward, pendulum-wise,  and  partly  by  muscular  action;  the  muscles  used 
being, — Ist,  those  on  the  front  of  the  thigh,  which  bend  the  thigh  for- 
ward on  the  pelvis,  especially  the  rectus  femoris,  with  the  psoas  and  the 
iliacus;  2ndly,  the  hamstring  muscles,  which  slightly  bend  the  leg  on  the 
thigh;  and  Srdly,  the  muscles  on  the  front  of  the  leg,  which  raise  the 
front  of  the  foot  and  toes,  and  so  prevent  the  latter  in  swinging  forward 
from  hitching  in  the  ground. 

The  second  part  of  the  act  of  walking,  which  has  been  just  described, 
is  shown  in  the  diagram  (4,  Fig.  291). 

When  the  right  foot  has  reached  the  ground  the  action  of  the  left  leg 
has  not  ceased.  The  calf -muscles  of  the  latter  continue  to  act,  and  by 
pulling  up  the  heel,  throw  the  body  still  more  forward  over  the  right  leg, 
now  bearing  nearly  the  whole  weight,  until  it  is  time  that  in  its  turn 
the  left  leg  should  swing  forward,  and  the  left  foot  be  planted  on  the 
ground  to  prevent  the  body  from  falling  prostrate.    As  at  first,  while  the 


1  2  3  4  5 

Fig.  291. 


calf -muscles  of  one  leg  and  foot  are  preparing,  so  to  speak,  to  push  the 
body  forward  and  upward  from  behind  by  raising  the  heel,  the  muscles  on 
the  front  of  the  trunk  and  of  the  same  leg  (and  of  the  other  leg,  except 
when  it  is  swinging  forward)  are  helping  the  act  hy  pulling  the  legs  and 
trunk,  so  as  to  make  them  incline  forward,  the  rotation  in  the  inclining  for- 
ward being  effected  mainly  at  the  ankle  joint.  Two  main  kinds  of  lever- 
age are,  therefore,  employed  in  the  act  of  walking,  and  if  this  idea  be 
firmly  grasped,  the  detail  will  be  understood  with  comparative  ease.  One 
kind  of  leverage  employed  in  walking  is  essentially  the  same  witli  that 
employed  in  pulling  forward  the  pole,  as  in  Fig.  290.  And  tlie  other, 
less  exactly,  is  that  employed  in  raising  the  handles  of  a  wheelbarrow. 
Now,  supposing  tlie  lower  end  of  the  pole  to  be  placed  in  tlie  barrow,  we 
should  have  a  very  rough  and  inelegant,  but  not  altogether  bad  repre- 
sentation of  the  two  main  levers  employed  in  tlie  act  of  walking.  The 
body  is  pulled  forward  by  the  muscles  in  front,  much  in  the  same  way  that 
the  pole  might  be  by  tlie  force  applied  at  p  (Fig.  290),  while  the  raising 
of  the  heel  and  pushing  forward  of  the  trunk  by  the  calf -muscles  is  roughly 
represented  on  raising  the  handles  of  the  barrow.  The  manner  in  which 
these  actions  are  iierformed  alternately  by  each  leg,  so  that  one  after  the 
other  is  swung  forward  to  support  the  trunk,  which  is  at  the  same 
time  pushed  and  pulled  forward  by  the  muscles  of  the  other,  may  be 
gathered  from  the  previous  description. 


CAUSES  AND  PHENOMENA  OF  MOTION. 


43 


There  is  one  more  thing  to  be  noticed  especially  in  the  act  of  walking. 
Inasmuch  as  the  body  is  being  constantly  supported  and  balanced  on  each 
leg  alternately,  and  therefore  on  only  one  at  the  same  moment,  it  is  evi- 
dent that  there  must  be  some  provision  made  for  throwing  the  centre  of 
gravity  over  the  line  of  support  formed  by  the  bones  of  each  leg,  as,  in  its 
turn,  it  supports  the  weight  of  the  body.  This  may  be  done  in  various 
ways,  and  the  manner  in  which  it  is  effected  is  one  element  in  the  differ- 
ences which  exist  in  the  walking  of  different  people.  Thus  it  may  be 
done  by  an  instinctive  slight  rotation  of  the  pelvis  on  the  head  of  each 
femur  in  turn,  in  such  a  manner  that  the  centre  of  gravity  of  the  body 
shall  fall  over  the  foot  of  this  side.  Thus  when  the  body  is  pushed  on- 
ward and  upward  by  the  raising,  say,  of  the  right  heel,  as  in  Fig.  291,  3, 
the  pelvis  is  instinctively  by  various  muscles,  made  to  rotate  on  the  head 
of  the  left  femur  at  the  acetabulum,  to  the  left  side,  so  that  the  weight 
may  fall  over  the  line  of  support  formed  by  the  left  leg  at  the  time  that 
the  right  leg  is  swinging  forward,  and  leaving  all  the  work  of  support  to 
fall  on  its  fellow.  Such  a  "rocking''  movement  of  the  trunk  and  pelvis, 
however,  is  accompanied  by  a  movement  of  the  whole  trunk  and  leg  over 
the  foot  which  is  being  planted  on  the  ground  (Fig.  29J^);  the  action 


Fig.  292. 

being  accompanied  with  a  compensatory  outward  movement  at  the  hip, 
more  easily  appreciated  by  looking  at  the  figure  (in  which  this  movement 
is  shown  exaggerated)  than  described. 

Thus  the  body  in  walking  is  continually  rising  and  swaying  alternately 
from  one  side  to  the  other,  as  its  centre  of  gravity  has  to  be  brought  alter- 
nately over  one  or  other  leg;  and  the  curvatures  of  the  spine  are  altered 
in  correspondence  with  the  varying  position  of  the  weight  which  it  has 
to  support.  The  extent  to  which  the  body  is  raised  or  swayed  differs  much 
in  different  people. 

In  walking,  one  foot  or  the  other  is  always  on  the  ground.  The  act 
of  leaping  ox  jumping,  consists  in  so  sudden  a  raising  of  the  heels  by  the 
sharp  and  strong  contraction  of  the  calf-muscles,  that  the  body  is  jerked 


44 


HAND-BOOK  OF  PHYSIOLOGY. 


off  the  gi'onnd.  At  the  same  time  tlie  effect  is  much  increased  by  first 
bending  the  thighs  on  the  pelvis,  and  the  legs  on  the  thighs,  and  then 
suddenly  straightening  out  the  angles  thus  formed.  The  share  which 
this  action  hcis  in  producing  the  effect  may  be  easily  known  by  attempt- 
ing to  leap  in  the  upright  posture,  with  the  legs  quite  straight. 

RiDDiing  is  performed  by  a  series  of  rapid  low  jumps  with  each  leg 
alternately;  so  that,  during  each  complete  muscular  act  concerned,  there 
is  a  moment  wdien  both  feet  are  off  the  ground. 

In  all  these  cases,  howeyer,  the  description  of  the  manner  in  which 
any  given  effect  is  produced,  can  give  but  a  very  imperfect  idea  of  the  in- 
finite number  of  combined  and  harmoniously  arranged  muscular  contrac- 
tions which  are  necessary  for  even  the  simplest  acts  of  locomotion. 

Actions  of  the  Involuntary  Muscles.— The  involuntary  muscles 

are  for  the  most  part  not  attached  to  bones  arranged  to  act  as  levers,  but 
enter  into  the  formation  of  such  hollow  parts  as  require  a  diminution  of 
their  calibre  by  muscular  action,  under  particular  circumstances.  Ex- 
amples of  this  action  are  to  be  found  in  the  intestines,  urinary  bladder, 
heart  and  blood-vessels,  gall-bladder,  gland-ducts,  etc. 

The  difference  in  the  manner  of  contraction  of  the  striated  and  non- 
striated  fibres  has  been  already  referred  to  (p.  36,  Vol.  II.);  and  the  pecu- 
liar vermicular  or  peristaltic  action  of  the  latter  fibres  has  been  described 
at  p.  36,  Vol.  II. 

Source  of  Musculati  Action. 

It  was  formerly  supposed  that  each  act  of  contraction  on  the  part  of 
a  muscle  was  accompanied  by  a  correlative  waste  or  destruction  of  its  own 
substance;  and  that  the  quantity  of  the  nitrogenous  excreta,  especially  of 
urea,  presumably  the  expression  of  this  waste,  was  in  exact  pi'oportion  to 
the  amount  of  muscular  work  performed.  It  has  been  found,  however, 
both  that  the  theory  itself  is  erroneous,  and  that  the  supposed  facts  on 
which  it  was  founded  do  not  exist. 

It  is  true  that  in  the  action  of  muscles,  as  of  all  other  parts,  there  is  a 
certain  destruction  of  tissue,  or,  in  other  words,  a  certain  "wear  and  tear," 
wdiich  may  be  represented  by  a  slight  increase  in  the  quantity  of  urea 
excreted:  but  it  is  not  the  correlative  expression  or  only  source  of  the 
power  manifested.  The  increase  in  the  amount  of  urea  which  is  excreted 
after  muscular  exertion  is  by  no  means  so  great  as  was  formerly  supposed; 
indeed,  it  is  very  slight.  And  as  there  is  no  reason  to  believ  ethat  the 
waste  of  muscle-substance  can  be  expressed,  with  unimportant  exceptions, 
in  any  other  way  than  by  an  increased  excretion  of  urea,  it  is  evident  that 
we  must  look  elsewhere  than  in  destruction  of  muscle,  for  the  source  of 
muscular  action.  For,  it  need  scarcely  be  said,  all  force  manifested  in  the 
living  body  must  be  the  correlative  expression  of  force  previously  latent  in 
the  food  eaten  or  the  tissue  formed;  and  evidences  of  force  expended  in 


CAUSES  AND  PHENOMENA  OF  MOTION. 


45 


the  body  must  be  found  in  the  excreta.  If,  therefore,  the  nitrogeiioiis 
excreta,  represented  chiefly  by  urea,  are  not  in  sufficient  quantity  to 
account  for  the  work  done,  we  must  look  to  the  non-nitroge?ious  excreta  as 
carbonic  acid  and  water,  which,  presumably,  cannot  be  the  expression  of 
wasted  muscle- substance. 

The  quantity  of  these  non-nitrogenous  excreta  is  undoubtedly  increased 
by  active  muscular  efforts,  and  to  a  considerable  extent;  and  whatever 
may  be  the  source  of  the  water,  the  carbonic  acid,  at  least,  is  the  result 
of  chemical  action  in  the  system,  and  especially  of  the  combustion  of  non- 
nitrogenous  food,  although,  doubtless,  of  nitrogenous  food  also.  We  are, 
therefore,  driven  to  the  conclusion, — that  the  substance  of  muscles  is  not 
wasted  in  proportion  to  the  work  they  perform;  and  that  the  non-nitrog- 
enous as  well  as  the  nitrogenous  foods  may,  in  their  combustion,  afford 
the  requisite  conditions  for  muscular  action.  The  urgent  necessity  for 
nitrogenous  food,  especially  after  exercise,  is  probably  due  more  to  the 
need  of  nutrition  by  the  exhausted  muscles  and  other  tissues  for  which, 
of  course,  nitrogen  is  essential,  than  to  such  food  being  superior  to  non- 
nitrogenous  substances  as  a  source  of  muscular  power. 

The  electrical  condition  of  N"erves  is  so  closely  connected  with  the 
phenomena  of  muscular  contraction,  that  it  will  be  convenient  to  consider 
it  in  the  present  chapter. 

Electrical  currents  in  Nerves. — If  a  piece  of  nerve  be  removed  from 
the  body  and  subjected  to  examination  in  a  way  similar  to  that  adopted  in 
the  case  of  muscle  which  has  been  described  (p.  22,  Vol.  II.),  electrical  cur- 
rents are  found  to  exist  which  correspond  exactly  to  the  natural  muscle 
currents,  and  which  are  called  natural  nerve  currents  or  currents  of  rest, 
according  as  one  or  other  theory  of  their  existence  be  adopted,  as  in  the 
case  with  muscle.  One  point  (corresponding  to  the  equator)  on  the  sur- 
face being  positive  to  all  other  points  neare**  to  the  cut  ends,  and  the 
greatest  deflection  of  the  needle  of  the  galvanometer  taking  place  when 
one  electrode  is  applied  to  the  equator  and  the  other  to  the  centre  of  either 
cut  end.  As  in  the  case  of  muscle,  these  nerve-currents  undergo  a  negative 
variation  when  the  nerve  is  stimulated,  the  variation  being  momentary 
and  in  the  opposite  direction  to  the  natural  currents;  and  are  similarly 
known  as  the  currents  of  action.  The  currents  of  action  are  propagated 
in  both  directions  from  the  point  of  the  application  of  the  stimulus,  and 
are  of  momentary  duration. 

Rheoscopic  Frog". — The  negative  variation  of  the  nerve  current 
may  be  demonstrated  by  means  of  the  following  experiment. — The  new 
current  produced  by  stimulating  the  nerve  of  one  nerve-muscle  prepara- 
tion may  be  used  to  stimulate  the  nerve  of  a  second  nerve-muscle  prepa- 
ration. The  fore-leg  of  a  frog  with  the  nerve  going  to  the  gastrocnemius 
cut  long  is  placed  upon  a  glass  plate,  and  arranged  in  such  a  way  that  its 
nerve  touches  in  two  places  the  sciatic  nerve,  exposed  but  preserved  i7i 


46 


HAND-BOOK  OF  PHYSIOLOGY. 


situ  in  the  thigh  of  the  opposite  leg.  The  electrodes  from  an  induction 
coil  are  placed  behind  the  sciatic  nerve  of  the  second  preparation,  high 
up.  On  stimulating  the  nerve  with  a  single  induction  shock,  the  muscles 
not  only  of  the  same  leg  are  found  to  undergo  a  twitch,  but  also  those  of 
the  first  preparation,  although  this  is  not  near  the  electrodes,  and  so  the 
stimulation  cannot  be  due  to  an  escape  of  the  current  into  the  first  nerve. 
This  experiment  is  known  under  the  name  of  the  rheoscopic  frog. 

Nerve-stimuli. — Nerve-fibres  require  to  be  stimulated  before  they 
can  manifest  any  of  their  properties,  since  they  have  no  power  of  them- 
selves of  generating  force  or  of  originating  impulses.  The  stimuli  which 
are  capable  of  exciting  nerves  to  action,  are,  as  in  the  case  of  muscle,  very 
diverse.  They  are  of  very  similar  nature  in  each  case.  The  mechanical, 
chemical,  thermal,  and  electric  stimuli  which  may  be  used  in  the  one  case 
are  also,  with  certain  differences  in  the  methods  employed,  efficacious  in 
the  other.  The  chemical  stimuli  are  chiefly  these:  withdrawal  of  water, 
as  by  drying,  strong  solutions  of  neutral  salts  of  potassium,  sodium,  etc., 
free  inorganic  acids,  except  phosphoric;  some  organic  acids;  ether,  chloro- 
form, and  bile  salts.  The  electrical  stimuli  employed  are  the  induction 
and  continuous  currents  concerning  which  the  observations  in  reference  to 
muscular  contraction  should  be  consulted,  p.  26,  et  seq.,  Vol.  II.  Weaker 
electrical  stimuli  will  excite  nerve  than  will  excite  muscle;  the  nerve 
stimulus  appears  to  gain  strength  as  it  descends,  and  a  weaker  stimulus 
applied  far  from  the  muscle  will  have  the  same  effect  as  a  somewhat 
stronger  one  applied  to  the  nerve  near  the  muscle. 

It  will  be  only  necessary  here  to  add  some  account  of  the  effect  of  a 
constant  electrical  current,  such  as  that  obtained  from  DanielFs  battery, 
upon  a  nerve.  This  effect  may  be  studied  with  the  apparatus  described 
before.  A  pair  of  electrodes  are  placed  behind  the  nerve  of  the  nerve- 
muscle  preparation,  with  a*Du  Bois  Reymond's  key  arranged  for  short 
circuiting  the  battery  current,  in  such  a  way  that  when  the  key  is  opened 
the  current  is  sent  into  the  nerve,  and  when  closed  the  current  is  cut  off. 
It  will  be  found  that  with  a  current  of  moderate  strength  there  will  be  a 
contraction  of  the  muscle  both  at  the  opening  and  at  the  closing  of  the 
key  (called  respectively  mahing  and  breaking  contractions),  but  that 
during  the  interval  between  these  two  events  the  muscle  remains  flaccid, 
provided  the  battery  current  continues  of  constant  intensity.  If  the  cur- 
rent be  a  very  weak  or  a  very  strong  one  the  effect  is  not  quite  the  same; 
one  or  other  of  the  contractions  may  be  absent.  Which  of  these  con- 
tractions is  absent  depends  upon  another  circumstance,  viz.,  the  direction 
of  the  current.  The  direction  of  the  current  may  be  ascending  or  de- 
scending; if  ascending,  the  anode  or  positive  pole  is  nearer  the  muscle 
than  the  kathode  or  negative  pole,  and  the  current  to  return  to  the  bat- 
tery has  to  pass  up  tlie  nerve, — if  descending,  tlie  position  of  tlie  electrodes 
is  reversed.    It  will  be  necessary  before  considering  tliis  question  further 


CAUSES  AND  PHENOMENA  OF  MOTION. 


47 


to  return  to  the  want  of  apparent  effect  of  the  constant  current  during 
the  interval  between  the  make  and  break  contraction:  to  all  appearance, 
indeed,  no  effect  is  produced  at  all,  but  in  reality  a  very  important  change 
is  brought  about  in  the  nerve  by  the  passage  of  the  current.  This  may 
be  shown  in  two  ways,  first  of  all  by  the  galvanometer.  If  a  piece  of 
nerve  be  taken,  and  if  at  either  end  an  arrangement  be  made  to  test  the 
electrical  condition  of  the  nerve  by  means  of  a  pair  of  non-polarizable 
electrodes  connected  with  a  galvanometer,  while  to  the  central  portion 
a  pair  of  electrodes  connected  with  a  Daniell's  battery  be  applied,  it  will 
be  found  that  the  natural  nerve-currents  are  profoundly  altered  on  the 
passage  of  the  constant  current  (which  is  called  the  polarizing  current) 
in  the  neighborhood.  If  the  polarizing  current  be  in  the  same  direction 
as  the  latter  the  natural  current  is  increased,  but  if  in  the  direction  oppo- 
site to  it,  the  natural  current  is  diminished.  This  change,  produced  by 
the  continual  passage  of  the  battery-current  through  a  portion  of  the 
nerve  is  to  be  distinguished  from  the  negative  variation  of  the  natural  cur- 
rent to  which  allusion  has  been  already  made,  and  which  is  a  momentary 
change  occurring  on  the  sudden  application  of  the  stimulus.  The  con- 
dition produced  in  a  nerve  by  the  passage  of  a  constant  current  is  known 
by  the  name  of  electrotonios. 

The  other  way  of  showing  the  effect  of  the  same  polarizing  current  is 
by  taking  a  nerve-muscle  preparation  and  applying  to  the  nerves  a  pair 
of  electrodes  from  an  induction  coil  whilst  at  a  point  further  removed  from 
the  muscle,  electrodes  from  a  DanielFs  battery  are  arranged  with  a  key 
for  short  circuiting  and  an  apparatus  (reverser)  by  which  the  battery  cur- 
rent may  be  reversed  in  direction.  If  the  exact  point  be  ascertained  to 
which  the  secondary  coil  should  be  moved  from  the  primary  coil  in  order 
that  a  minimum  contraction  be  obtained  by  the  induction  shock,  and 
the  secondary  coil  be  removed  slightly  further  from  the  primary,  the  in- 
duction current  cannot  now  produce  a  contraction;  but  if  the  polarizing 
current  be  sent  in  a  descending  direction,  that  is  to  say,  with  the  kathode 
nearest  the  other  electrodes,  the  induction  current,  which  was  before  in- 
sufficient, will  prove  sufficient  to  cause  a  contraction;  whereby  indicating 
that  with  a  descending  current  the  irritability  of  the  nerve  is  increased. 
By  means  of  a  somewhat  similar  experiment  it  may  be  shown  that  an 
ascending  current  will  diminish  the  irritability  of  a  nerve.  Similarly,  if 
instead  of  applying  the  induction  electrodes  below  the  other  electrodes  they 
are  applied  between  them,  like  effects  are  demonstrated,  indicating  that 
in  the  neighborhood  of  the  kathode  the  irritability  of  the  nerve  is  in- 
creased by  a  constant  current,  and  in  the  neighborhood  of  the  anode 
diminished.  This  increase  in  irritability  is  called  Icatelectrotonus,  and 
similarly  the  decrease  is  called  anelectrotoniis.  As  there  is  between  the 
electrodes  both  an  increase  and  a  decrease  of  irritability  on  the  passage  of 
a  polarizing  current  it  must  be  evident  that  the  increase  must  shade  off 


48 


HAia)-BOOK  OF  PHYSIOLOGY. 


into  the  decrease,  and  that  there  must  be  a  neutral  point  where  there  is 
neither  increase  nor  decrease  of  irritability.  The  position  of  this  neutral 
point  is  found  to  vary  with  the  intensity  of  the  polarizing  current;  when 
the  current  is  weak  the  point  is  nearer  the  anode,  when  strong  nearer  the 
kathode  (Fig.  293).  "When  a  constant  current  passes  into  a  nerve,  there- 
fore, if  a  making  contraction  result,  it  may  be  assumed  that  it  is  due  to 


/ 

/ 

/  / 
/  X 
/  / 
/    y  .■ 

\ 

\ 

— ^ 

\  \ 

N 

Fig.  293.— Diagram  illnstratiBg  the  effects  of  various  intensities  of  the  polarizing  currents,  n,  n' 
nerre;  a,  anode;  A%  kathode;  the  curves  above  indicate  increase,  and  those  below  decrease  of  irrita- 
bihty,  and  when  the  current  is  small  the  increase  and  decrease  are  both  small,  with  the  neutral 
point  near  a,  and  so  on  as  the  current  is  increased  in  strength. 

the  increased  irritability  produced  in  the  neighborhood  of  the  kathode, 
but  the  breaking  contraction  must  be  produced  by  a  rise  in  irritability 
from  a  lowered  state  to  the  normal  in  the  neighborhood  of  the  anode. 
The  contractions  produced  in  the  muscle  of  a  nerve-muscle  preparation 
by  a  constant  current  have  been  arranged  in  a  table  which  is  known  as 
Pfliiger^s  Law  of  Contractions.  It  is  really  only  a  statement  as  to  when 
a  contraction  may  be  expected: — 


Descending  Current. 


Make. 

Break. 

Weak  .    .  . 

Yes. 

Xo. 

Moderate .  . 

Yes. 

Yes. 

Strong     .  . 

Yes. 

No. 

Ascending  Current. 


Make. 

Break. 

Yes. 

No. 

Yes. 

Yes. 

No. 

Yes. 

The  difficulty  in  this  table  is  chiefly  in  the  effect  of  a  weak  current, 
but  the  following  statement  will  explain  it.  The  increase  of  irritability 
at  the  kathode  is  more  potent  to  produce  a  contraction  than  the  rise  of 
irritability  from  a  lower  to  a  normal  condition  at  the  anode.  With  weak 
currents  the  only  effect  is  a  contraction  at  the  make  of  both  ascending 
and  descending  currents,  the  descending  current  being  more  potent  than 
the  ascending  (and  with  still  weaker  currents  is  the  only  one  which  pro- 
duces any  effect),  since  the  kathode  is  near  the  muscle,  whereas  in  the 
case  of  the  ascending  current  the  stimulus  has  to  pass  through  a  district 
of  diminished  irritability,  which  may  either  act  as  an  entire  block,  or 
may  diminish  slightly  the  contraction  which  follows.    As  the  polarizing 


CAUSES  AND  PHENOMENA  OF  MOTION. 


49 


current  becomes  stronger,  recovery  from  anelectrotonus  is  able  to  produce 
a  contraction  as  well  as  katelectrotonus,  and  a  contraction  occurs  both 
at  the  make  and  the  break  of  the  current.  The  absence  of  contraction 
with  a  very  strong  current  at  the  break  of  the  ascending  current  may  be 
explained  by  supposing  that  the  region  of  fall  in  irritability  at  the  kathode 
blocks  the  stimulus  of  the  rise  in  irritability  at  the  anode. 

Thus  we  have  seen  that  two  circumstances  influence  the  effect  of  the 
constant  current  upon  a  nerve,  viz.,  the  strength  and  direction  of  the 
current.  It  is  also  necessary  that  the  stimulus  should  be  applied  sud- 
denly and  not  gradually,  and  that  the  irritability  of  the  nerve  be  normal, 
and  not  increased  or  diminished.  Sometimes  (when  the  nerve  is  specially 
irritable?)  instead  of  a  simple  contraction  a  tetanus  occurs  at  the  make 
or  break  of  the  constant  current.  This  is  especially  liable  to  occur  at 
the  break  of  a  strong  ascending  current  which  has  been  passing  for  some 
time  into  the  preparation;  this  is  called  Rittefs  tetanus,  and  may  be 
increased  by  passing  a  current  in  an  opposite  direction  or  stopped  by 
passing  a  current  in  the  same  direction. 


Vol.  II.~4 


CHAPTER  XVI. 


THE  VOICE  AND  SPEECH. 

Ik  nearly  all  air-breathing  vertebrate  animals  there  are  arrangements 
for  the  production  of  sound,  or  voice,  in  some  parts  of  the  respiratory 
apparatus.  In  many  animals,  the  sound  admits  of  being  variously  modi- 
fied and  altered  during  and  after  its  production;  and,  in  man,  one  such 
modification  occurring  in  obedience  to  dictates  of  the  cerebrum,  is  speecli. 

Mode  of  Productioj^"  of  the  HuMAi^"  Voice. 

It  has  been  proved  by  observations  on  living  subjects,  by  means  of  the 
laryngoscope,  as  well  as  by  experiments  on  the  larynx  taken  from  the 
dead  body,  that  the  sound  of  the  human  voice  is  the  result  of  the  inferior 
laryngeal  ligaments,  or  true  vocal  cords  (A,  cv,  Fig.  298)  which  bound 
the  glottis,  being  thrown  into  vibration  by  currents  of  expired  air  impelled 
over  their  edges.  Thus,  if  a  free  opening  exists  in  the  trachea,  the  sound 
of  the  voice  ceases,  but  returns  if  the  opening  is  closed.  An  opening 
into  the  air-passages  above  the  glottis,  on  the  contrary,  does  not  prevent 
the  voice  being  formed.  Injury  of  the  laryngeal  nerves  su]3plying  the 
muscles  which  move  the  vocal  cords  puts  an  end  to  the  formation  of 
vocal  sounds;  and  when  these  nerves  are  divided  on  both  sides,  the  loss 
of  voice  is  complete.  Moreover,  by  forcing  a  current  of  air  through  the 
larynx  in  the  dead  subject,  clear  vocal  sounds  are  produced,  though  the 
epiglottis,  the  upper  ligaments  of  the  larynx  or  false  vocal  cords,  the 
ventricles  between  them  and  the  inferior  ligaments  or  true  vocal  cords, 
and  the  upper  part  of  the  arytenoid  cartilages,  be  all  removed;  provided 
the  true  vocal  cords  remain  entire,  with  their  points  of  attachment,  and 
be  kept  tense  and  so  approximated  that  the  fissure  of  the  glottis  may  be 
narrow. 

The  vocal  ligaments  or  cords,  therefore,  may  be  regarded  as  the  proper 
organs  of  the  mere  voice:  the  modifications  of  the  voice  being  effected  l)y 
other  parts — tongue,  teeth,  lips,  etc.,  as  well  as  by  them.  The  structure 
of  the  vocal  cords  is  adapted  to  enable  them  to  vibrate  like  tense  mem- 
branes, for  they  are  essentially  composed  of  elastic  tissue;  and  they  are 
so  attached  to  the  cartilaginous  parts  of  the  larynx  that  their  position 
and  tension  can  be  variously  altered  by  the  contraction  of  the  muscles 
which  act  On  these  parts. 


THE  VOICE  AND  SPEECH. 


51 


The  Larynx. — The  larynx,  or  organ  of  voice,  consists  essentially  of 
the  two  vocal  cords,  which  are  so  attached  to  certain  cartilages,  and  so 
under  the  control  of  certain  muscles,  that  they  can  be  made  the  means 
not  only  of  closing  the  aperture  of  the  larynx  (rima  glottidis),  of  which 
they  are  the  lateral  boundaries,  against  the  entrance  and  exit  of  air  to  or 


r 


Fig.  294.  Fig.  295. 

Fig.  294.— Outline  showing  the  general  form  of  the  larynx,  trachea,  and  bronchi,  as  seen  from 
before,  h,  the  great  cornu  of  the  hyoid  bone;  e,  epiglottis;  ^,  superior,  and  t\  inferior  cornu  of  the 
thyroid  cartilage;  c,  middle  of  the  cricoid  cartilage;  tr,  the  trachea,  showing  sixteen  cartilaginous 
nngs;  6,  the  right,  and  6',  the  left  bronchus.    X  Y^.   (Allen  Thomson.) 

FiG-  295.— Outhne  showing  the  general  form  of  the  larynx,  trachea,  and  bronchi,  as  seen  from 
behind,  /i,  great  cornu  of  the  hyoid  bone;  t,  superior,  and  t',  the  inferior  cornu  of  the  thyroid  carti- 
lage; e,  the  epiglottis;  a,  points  to  the  back  of  both  the  arytenoid  cartilages,  which  are  surmounted 
by  the  cornicula;  c,  the  middle  ridge  on  the  back  of  the  cricoid  cartilage;  tr,  the  posterior  mem- 
branous part  of  the  trachea;  6,  6',  right  and  left  bronchi,    x  Y^.   (Allen  Thomson.) 

from  the  lungs,  but  also  can  be  stretched  or  relaxed,  shortened  or  length- 
ened, in  accordance  with  the  conditions  that  may  be  necessary  for  the  air 
in  passing  over  them,  to  set  them  vibrating  and  produce  various  sounds. 


52 


HAND-BOOK  OF  PHYSIOLOGY. 


Their  action  in  respiration  has  been  already  referred  to  (p.  189,  VoL  I.). 
In  the  present  chapter  the  sound  produced  by  the  vibration  of  the  vocal 
cords  is  the  only  part  of  their  function  with  which  we  have  to  deal. 

Anatomy  of  tlie  Larynx. — The  principal  parts  entering  into  the  for- 
mation of  the  larynx  (Figs.  294  and  295)  are — (t)  the  thyroid  cartilage;  (c) 
the  cricoid  cartilage;  {a)  the  two  arytenoid  cartilages;  and  the  two  true 
vocal  cords  (A,  cv,  Fig.  298).  The  epiglottis  (Fig.  298  e),  has  but  little 
to  do  with  the  voice,  and  is  chiefly  useful  in  falling  down  as  a  "lid"  over 
the  upper  part  of  the  larynx,  to  help  in  preventing  the  entrance  of  food 
and  drink  in  deglutition.  It  also  guides  mucus  or  other  fluids  in  small 
amount  from  the  mouth  around  the  sides  of  the  upper  opening  of  the 
glottis  into  the  pharynx  and  oesophagus:  thus  preventing  them  from 
entering  the  larynx.  The  false  vocal  cords  {cvs,  Fig.  298),  and  the  ven- 
tricle of  the  larynx,  which  is  a  space  between  the  false  and  the  true  cord 
of  either  side,  need  be  here  only  referred  to. 

Cartilages. — The  thyroid  cartilage  (Fig.  296,  1  to  4)  does  not  form  a 
complete  ring  around  the  larynx,  but  only  covers  the  front  portion.  The 


Fig.  296.  Fig.  297. 

Fig.  296.— Cartilages  of  the  larynx  seen  from  before.  1  to  4,  thyroid  cartilage;  1,  vertical  ridge 
or  pomiim  Adami;  2,  right  ala;  3,  superior,  and  4,  inferior  cornu  of  the  right  side;  5,  6,  cricoid  carti- 
lage; 5,  inside  of  the  posterior  part;  6,  anterior  narrow  part  of  the  ring;  7,  arytenoid  cartilages,  x 

Fig.  297.— Lateral  view  of  exterior  of  the  larynx.  8,  thyroid  cartilage;  9,  cricoid  cartilage;  1(), 
crico-thyroid  muscle;  11,  crico-thyroid  ligament;  12,  first  rings  of  trachea.  (Willis.) 

cricoid  cartilage  (Fig.  296,  5,  6),  on  the  other  hand,  is  a  complete  ring; 
the  back  part  of  the  ring  being  much  broader  than  the  front.  On  the 
top  of  this  broad  portion  of  the  cricoid  are  the  arytenoid  cartilages  (Fig. 
298  a)  the  connection  between  the  cricoid  below  and  arytenoid  cartilages 
above  being  a  joint  with  synovial  membrane  and  ligaments,  the  latter 
permitting  tolerably  free  motion  between  them.  But  although  the 
arytenoid  cartilages  can  move  on  the  cricoid,  they  of  course  accompany 
the  latter  in  all  their  movements,  just  as  the  head  may  nod  or  turn  on 


THE  VOICE  AND  SPEECH. 


53 


the  top  of  the  spinal  column,  but  must  accompany  it  in  all  its  movements 
as  a  whole. 

Ligaments. — The  thyroid  cartilage  is  also  connected  with  the  cricoid, 
not  only  by  ligaments,  but  by  two  Joints  with  synovial  membrane  (f, 
Figs.  294  and  295);  the  lower  cornua  of  the  thyroid  clasping,  or  nipping, 
as  it  were,  the  cricoid  between  them,  but  not  so  tightly  but  that  the  thy- 
roid can  revolve,  within  a  certain  range,  around  an  axis  passing  trans- 
versely through  the  two  joints  at  which  the  cricoid  is  clasped.  The  vocal 
cords  are  attached  (behind)  to  the  front  portion  of  the  base  of  the  arytenoid 
cartilages,  and  (in  front)  to  the  re-entering  angle  at  the  back  part  of  the 
thyroid;  it  is  evident,  therefore,  that  all  movements  of  either  of  these 
cartilages  must  produce  an  effect  on  them  of  some  kind  or  other.  Inas- 
much, too,  as  the  arytenoid  cartilages  rest  on  the  top  of  the  back  portion 
of  the  cricoid  cartilage  (a,  Fig.  298),  and  are  connected  with  it  by  cap- 
sular and  other  ligaments,  all  movements  of  the  cricoid  cartilage  must 
move  the  arytenoid  cartilages,  and  also  produce  an  effect  on  the  vocal  cords. 

Intrinsic  Muscles. — The  so-called  intrinsic  muscles  of  the  larynx,  or 
those  which,  in  their  action,  have  a  direct  action  on  the  vocal  cords,  are 
nine  in  number — four  pairs,  and  a  single  muscle;  namely,  two  crico- 
thyroid muscles,  two  tliyro-arytenoid,  two  posterior  crico-arytenoid,  two 
lateral  crico-arytenoid,  and  one  arytenoid  muscle.  Their  actions  are  as 
follows: — When  the  crico-tliyroid  muscles  (10,  Eig.  297)  contract,  they 
rotate  the  cricoid  on  the  thyroid  cartilage  in  such  a  manner  that  the 
upper  and  back  part  of  the  former,  and  of  necessity  the  arytenoid 
cartilages  on  the  top  of  it,  are  tipped  backward,  while  the  thyroid  is  in- 
clined forward:  and  thus,  of  course,  the  vocal  cords  being  attached  in 
front  to  one,  and  behind  to  the  other,  are  ''put  on  the  stretch." 

The  tliyro-arytenoid  muscles  (7,  Fig.  300)  on  the  other  hand,  have  an 
opposite  action, — pulling  the  thyroid  backward,  and  the  arytenoid  and 
upper  and  back  part  of  the  cricoid  cartilages  forward,  and  thus  relaxing 
the  vocal  cords. 

The  crico-arytenoidei  posticus  muscles  (Fig.  299,  d)  dilate  the  glottis, 
and  separate  the  vocal  cords,  the  one  from  the  other,  by  an  action  on  the 
arytenoid  cartilage  which  will  be  plain  on  reference  to  B'  and  0',  (Fig. 
298).  By  their  contraction  they  tend  to  pull  together  the  outer  angles 
of  the  arytenoid  cartilages  in  such  a  fashion  as  to  rotate  the  latter  at  their 
joint  with  the  cricoid,  and  of  course  to  throw  asunder  their  anterior 
angles  to  which  the  vocal  cords  are  attached. 

These  posterior  crico-arytenoid  muscles  are  opposed  by  the  crico-aryte- 
noidei laterales,  which,  pulling  in  the  opposite  direction  from  the  other 
side  of  the  axis  of  rotation,  have  of  course  exactly  the  opposite  effect,  and 
close  the  glottis  (Fig.  300,  4  and  5). 

The  aperture  of  the  glottis  can  be  also  contracted  by  the  arytenoid 
muscle  (5,  Fig.  299,  and  6,  Fig.  300),  which,  in  its  contraction,  pulls 
together  the  upper  parts  of  the  arytenoid  cartilages  between  which  it 
extends. 

Nerve  supply. — In  the  performance  of  the  functions  of  the  larynx  the 
sensory  filaments  of  the  pneumogastric  supply  that  acute  sensibility  by 
which  the  glottis  is  s^narded  against  the  ingress  of  foreign  bodies,  or  of 
irrespirable  gases.  The  contact  of  these  stimulates  the  filaments  of  the 
superior  laryngeal  branch  of  the  pneumogastric;  and  the  impression  con- 
veyed to  the  medulla  oblongata,  whether  it  produce  sensation  or  not,  is 
reflected  to  the  filaments  of  the  recurrent  or  inferior  laryngeal  branch, 


54 


HAND-BOOK  OF  PHYSIOLOGY. 


and  excites  contraction  of  the  muscles  that  close  the  glottis.  Both  these 
branches  of  pnenmogastric  co-operate  also  in  the  production  and  regula- 
tion of  the  voice;  the  inferior  laryngeal  determining  the  contraction  of 
the  muscles  that  vary  the  tension  of  the  vocal  cords,  and  the  superior 
laryngeal  conveying  to  the  mind  the  sensation  of  the  state  of  these 
muscles  necessary  for  their  continuous  guidance.  And  both  the  branches 
co-operate  in  the  actions  of  the  larynx  in  the  ordinary  slight  dilatation 
and  contraction  of  the  glottis  in  the  acts  of  expiration  and  inspiration, 
and  more  evidently  in  those  of  coughing  and  other  forcible  respiratory 
movements. 


Fig.  298.— Three  laryngoscopic  views  of  the  superior  aperture  of  the  laiynx  and  surrounding 
parts.  A.  the  glottis  during  the  emission  of  a  higli  note  in  singing;  B,  in  easy  and  quiet  inhalation  of 
air:  C,  in  the  state  of  widest  possible  dilatation,  as  in  inhahng  a  very  deep"  breath.  The  diagrams 
A',  B',  and  C,  have  been  added  to  Czermak's  figures,  to  show  in  horizontal  sections  of  the  glottis  the 
position  of  the  vocal  hgaments  and  arytenoid  cartilages  in  the  three  several  states  represented  in  the 
other  figures.  In  all  the  figures,  so  far  as  marked,  the  letters  indicate  the  parts  as  follows,  viz.:  I, 
the  base  of  the  tongue;  e,  the  upper  free  part  of  tlie  epiglottis;  e\  the  tubercle  or  cushion  of  the  epi- 
glottis; _p/(,  part  of  the  anterior  wall  of  the  pharynx  behind  the  larynx;  in  the  margin  of  the  arj-teno- 
epiglottidean  fold  u\  the  swelling  of  the  membrane  caused  by  the  cai-tilages  of  Wrisberg;  that 
of  the  cartilages  of  Santorini;  a,  the  tip  or  summit  of  the  arytenoid  cartilages;  c  r,  the  true  vocal 
cords  or  lips  of  the  rima  glottidis;  cvs,  the  superior  or  false  vocal  cords;  between  them  the  ventricle 
of  the  larynx;  in  C,  tris  placed  on  the  anterior  wall  of  the  receding  trachea,  and  h  indicates  the  com- 
mencement of  the  two  bronchi  beyond  the  bifurcation  which  may  oe  brought  into  view  in  this  state 
of  extreme  dilatation.   (Czermak.)   (From  Quain's  Anatomy.) 


Movements  of  Vocal  Cords.— The  placing  of  the  vocal  cords  in  a 
position  parallel  one  witli  the  other,  is  clfected  by  a  combined  action  of  the 
various  little  muscles  which  act  on  tliom — the  thyro-arytcnoidci  having, 
without  much  reason,  the  credit  of  taking  the  largest  sliare  in  tlie  pro- 
duction of  this  effect.    Fig.  298  is  intended  to  show  the  various  positions 


THE  VOICE  AND  SPEECH. 


55 


of  the  vocal  cord  under  different  circumstances.  Thus,  m  ordinary  tran- 
quil breathing,  the  opening  of  the  glottis  is  wide  and  triangular  (b) 
becoming  a  little  wider  at  each  inspiration,  and  a  little  narrower  at  each 
expiration.  On  making  a  rapid  and  deep  inspiration  the  opening  of  the 
glottis  is  widely  dilated  (as  in  c),  and  somewhat  lozenge-shaped.  At  the 
moment  of  the  emission  of  sound,  it  is  narrowed,  the  margins  of  the 
arytenoid  cartilages  being  brought  into  contact  and  the  edges  of  the  vocal 
cords  approximated  and  made  parallel,  at  the  same  time  that  their  tension 
is  much  increased.  The  higher  the  note  produced,  the  tenser  do  the 
cords  become  (Fig.  298,  a);  and  the  range  of  a  voice  depends,  of  course. 


Fig.  299.— View  of  the  larynx  and  part  of  the  trachea  from  behind,  with  the  muscles  dissected; 
h,  the  body  of  the  hyoid  bone;  e,  epiglottis;  t,  the  posterior  borders  of  the  thyroid  cartilage;  c,  the 
median  ridge  of  the  cricoid;  a,  upper  part  of  the  arytenoid;  s,  placed  on  one  of  the  oblique  fasciculi 
of  the  arjrtenoid  muscle ;  6,  left  posterior  crico-arytenoid  muscle;  ends  of  the  incomplete  cartilagi- 
nous rings  of  the  trachea;  I,  fibrous  membrane  crossing  the  back  of  the  trachea;  n,  muscular  fibres 
exposed  in  a  part  (from  Quain's  Anatomy). 

in  the  main,  on  the  extent  to  which  the  degree  of  tension  of  the  vocal 
cords  can  be  thus  altered.  In  the  production  of  a  high  note,  the  vocal 
cords  are  brought  well  within  sight,  so  as  to  be  plainly  visible  with  the 
help  of  the  laryngoscope.  In  the  utterance  of  grave  tones,  on  the  other 
hand,  the  epiglottis  is  depressed  and  brought  over  them,  and  the  arytenoid 
cartilages  look  as  if  they  were  trying  to  hide  themselves  under  it  (Fig. 
301).  The  epiglottis,  by  being  somewhat  pressed  down  so  as  to  cover  the 
superior  cavity  of  the  larynx,  serves  to  render  the  notes  deeper  in  tone, 
and  at  the  same  time  somewhat  duller,  just  as  covering  the  end  of  a 
short  tube  placed  in  front  of  caoutchouc  tongues  lowers  the  tone.  In 
no  other  respect  does  the  epiglottis  appear  to  have  any  effect  in  modify- 
ing the  vocal  sounds. 


56 


HAm)-BOOK  Of  physiology. 


The  degree  of  approximation  of  the  vocal  cords  also  usually  corre- 
sponds with  the  height  of  the  note  produced;  but  probably  not  always,  for 
the  width  of  the  aperture  has  no  essential  influence  on  the  height  of  the 
note,  as  long  as  the  vocal  cords  have  the  same  tension:  only  with  a  wide 
aperture,  the  tone  is  more  difficult  to  produce,  and  is  less  perfect,  the 
rushing  of  the  air  through  the  aperture  being  heard  at  the  same  time. 

No  true  vocal  sound  is  produced  at  the  posterior  part  of  the  aperture 
of  the  glottis,  that,  viz.,  which  is  formed  by  the  space  between  the  aryte- 


FiG.  300.— View  of  the  anterior  of  larynx  from  above.  1,  aperture  of  glottis;  2,  arytenoid  car- 
tilages; 3,  vocal  cords ;  4,  posterior  crico-arytenoid  muscles;  5,  lateral  crico-arytenoid  muscle  of  right 
side,  that  of  left  side  removed;  6,  arytenoid  muscle;  7,  thyro-arytenoid  muscle  of  left  side,  that  of 
right  side  removed;  8,  thyroid  cartilage;  9,  cricoid  cartilage;  13,  posterior  crico-arytenoid  ligament. 
(WiUis.) 

Fig.  301.— View  of  the  upper  part  of  the  larynx  as  seen  by  means  of  the  laryngoscope  during  the 
utterance  of  a  grave  note,  c,  epiglottis;  s,  tubercles  of  the  cartilages  of  Santorini;  a,  arji;enoid  car- 
tilages;    base  of  the  tongue;  hph,  the  posterior  wall  of  the  pharynx.  (Czermak.) 


noid  cartilages.  For,  as  Miiller^s  experiments  showed,  if  the  arytenoid 
cartilages  be  approximated  in  such  a  manner  that  their  anterior  jDrocesses 
touch  each  other,  but  yet  leave  an  opening  behind  them  as  well  as  in 
front,  no  second  vocal  tone  is  produced  by  the  passage  of  the  air  through 
the  posterior  opening,  but  merely  a  rustling  or  bubbling  sound;  and  the 
height  or  pitch  of  the  note  produced  is  the  same  whether  the  posterior 
part  of  the  glottis  be  open  or  not,  provided  the  vocal  cords  maintain  the 
same  degree  of  tension. 

Application^  of  the  Voice  m  Singing  and  Speaking. 

Varieties  of  Vocal  Sounds. — The  notes  of  the  voice  thus  produced 
may  observe  three  different  kinds  of  sequence.  Tlie  first  is  the  monoto- 
nous, in  which  the  notes  have  nearly  all  the  same  pitch  as  in  ordinary 
speaking;  the  variety  of  the  sounds  of  speech  being  due  to  articulation  in 
the  mouth.  In  s])caking,  liowever,  occasional  syllables  generally  receive  a 
higlier  intonation  for  the  sake  of  accent.  sccoiid  Diode  of  sequence 

is  the  successive  transition  from  high  to  low  notes,  and  vice  versd,  with- 
out intervals;  such  as  is  heard  in  the  sounds,  which,  as  expressions  of 


Fig.  300. 


Fig.  301. 


THE  VOICE  AND  SPEECH. 


57 


passion,  accompany  crying  in  men,  and  in  the  howling  and  whining  of 
dogs.  The  third  mode  of  sequence  of  the  vocal  sounds  is  the  musical,  in 
which  each  sound  has  a  determinate  number  of  vibrations,  and  the  num- 
bers of  the  vibrations  in  the  successive  sounds  have  the  same  relative  pro- 
portions that  characterize  the  notes  of  the  musical  scale. 

Compass  of  the  Voice. — In  different  individuals  this  comprehends 
•one,  two,  or  three  octaves.  In  singers — that  is,  in  persons  apt  for  sing- 
ing— it  extends  to  two  or  three  octaves.  But  the  male  and  female  voices 
commence  and  end  at  different  points  of  the  musical  scale.  The  lowest 
note  of  the  female  voice  is  about  an  octave  higher  than  the  lowest  of  the 
male  voice;  the  highest  note  of  the  female  voice  about  an  octave  higher 
than  the  highest  of  the  male.  *  The  compass  of  the  male  and  female 
voices  taken  together,  or  the  entire  scale  of  the  human  voice,  includes 
about  four  octaves.  The  principal  difference  between  the  male  and  female 
voice  is,  therefore,  in  their  pitch;  but  they  are  also  distinguished  by  their 
tone, — the  male  voice  is  not  so  soft. 

Pitch  and  Timbre. — The  voice  presents  other  varieties  besides  that 
of  male  and  female;  there  are  two  kinds  of  male  voice,  technically  called 
the  bass  and  tenor,  and  two  kinds  of  female  voice,  the  contralto  and 
soprano,  all  differing  from  each  other  in  tone.  The  bass  voice  usually 
reaches  lower  than  the  tenor,  and  its  strength  lies  in  the  low  notes;  while 
the  tenor  voice  extends  higher  than  the  bass.  The  contralto  voice  has 
generally  lower  notes  than  the  soprano,  and  is  strongest  in  the  lower 
notes  of  the  female  voice;  while  the  soprano  voice  reaches  higher  in  the 
scale.  But  the  difference  of  compass,  and  of  power  in  different  parts  of 
the  scale,  is  not  the  essential  distinction  between  the  different  voices;  for 
bass  singers  can  sometimes  go  very  high,  and  the  contralto  frequently 
sings  the  high  notes  like  soprano  singers.  The  essential  difference  be- 
tween the  bass  and  tenor  voices,  and  between  the  contralto  and  soprano, 
consists  in  their  tone  or  ''timbre,^^  which  distinguishes  them  even  when 
they  are  singing  the  same  note.  The  qualities  of  the  baritone  and  mezzo- 
soprano  voices  are  less  marked;  the  baritone  being  intermediate,  between 
the  bass  and  tenor,  the  mezzo-soprano  between  the  contralto  and  so])rano. 
They  have  also  a  middle  position  as  to  pitch  in  the  scale  of  the  male  and 
female  voices. 

The  different  pitch  of  the  male  and  the  female  voices  depends  on  the 
different  length  of  the  vocal  cords  in  the  two  sexes;  their  relative  length 
in  men  and  women  being  as  three  to  two.  The  difference  of  the  two 
voices  in  tone  or  ^ 'timbre,'^  is  owing  to  the  different  nature  and  form  of  the 
resounding  walls,  which  in  the  male  larynx  are  much  more  extensive,  and 
form  a  more  acute  angle  anteriorly.  The  different  qualities  of  the  tenor 
and  bass,  and  of  the  alto  and  soprano  voices,  probably  depend  on  some 
.peculiarities  of  the  ligaments,  and  the  membranous  and  cartilaginous 
parietes  of  the  laryngeal  cavity,  which  are  not  at  present  understood,  but 


58 


HAND-BOOK  OF  PHYSIOLOGY. 


of  which  we  may  form  some  idea,  by  recollecting  that  musical  instruments 
made  of  different  materials,  e.g.,  metallic  and  gut-strings,  nuiy  be  tuned 
to  the  same  note,  but  that  each  will  give  it  with  a  peculiar  tone  or 
"  timbre/' 

Varieties  of  Voices. — The  larynx  of  boys  resembles  the  female 
larynx;  their  vocal  cords  before  puberty  have  not  two-thirds  the  length 
which  they  acquire  at  that  period;  and  the  angle  of  their  thyroid  cartilage 
is  as  little  prominent  as  in  the  female  larynx.  Boys'  voices  are  alto  and 
soprano,  resembling  in  pitch  those  of  women,  but  louder,  and  differing 
somewhat  from  them  in  tone.  But,  after  the  larynx  has  undergone  the 
change  produced  during  the  period  of  development  at  puberty,  the  boy's 
voice  becomes  bass  or  tenor.  While  the  change  of  form  is  taking  place, 
the  voice  is  said  to  ''crack;"  it  becomes  imperfect,  frequently  hoarse  and 
crowing,  and  is  unfitted  for  singing  until  the  new  tones  are  brought 
under  command  by  practice.  In  eunuchs,  who  have  been  deprived  of 
the  testes  before  puberty,  the  voice  does  not  undergo  this  change.  The 
voice  of  most  old  people  is  deficient  in  tone,  unsteady,  and  more  restricted 
in  extent:  the  first  defect  is  owing  to  the  ossification  of  the  cartilages  of 
the  larynx  and  the  altered  condition  of  the  vocal  cord;  the  want  of  steadi- 
ness arises  from  the  loss  of  nervous  power  and  command  over  the  muscles; 
the  result  of  which  is  here,  as  in  other  parts,  a  tremulous  motion.  These 
two  causes  combined  render  the  voices  of  old  people  void  of  tone,  un- 
steady, bleating,  and  weak. 

In  any  class  of  persons  arranged,  as  in  an  orchestra,  according  to  the 
character  of  voices,  each  would  possess,  with  the  general  characteristics 
of  a  bass,  or  tenor,  or  any  other  kind  of  voice,  some  peculiar  character  by 
which  his  voice  would  be  recognized  from  all  the  rest.  The  conditions 
that  determine  these  distinctions  are,  however,  quite  unknown.  They 
are  probably  inherent  in  the  tissues  of  the  larynx,  and  are  as  indiscernible 
as  the  minute  differences  that  characterize  men's  features;  one  often  ob- 
serves, in  like  manner,  hereditary  and  family  peculiarities  of  voice,  as 
well  marked  as  those  of  the  limbs  or  face. 

Most  persons,  particularly  men,  have  the  power,  if  at  all  capable  of 
singing,  of  modulating  their  voices  through  a  double  series  of  notes  of 
different  character:  namely,  the  notes  of  the  natural  voice,  or  chest-notes, 
and  th.^  falsetto  notes.  The  natural  voice,  which  alone  has  been  hitherto 
considered,  is  fuller,  and  excites  a  distinct  sensation  of  much  stronger 
vibration  and  resonance  than  the  falsetto  voice,  which  has  more  a  flute-like 
character.  The  deeper  notes  of  the  male  voice  can  be  produced  only 
with  the  natural  voice,  the  highest  with  the  falsetto  only;  the  notes  of 
middle  pitch  can  be  produced  eitlier  with  the  natural  or  falsetto  voice; 
the  two  registers  of  the  voice  are  therefore  not  limited  in  sucli  a  manner 
as  that  one  ends  when  tlie  otlior  begins,  but  they  run  in  part  side  by  side. 

Method  of  the  Production  of  Notes. — The  natural  or  chest-notes 


THE  VOICE  AND  SPEECH. 


59 


are  produced  by  tiie  ordinary  vibrations  of  the  vocal  cords.  The  mode  of 
production  of  the  falsetto  notes  is  still  obscure. 

By  Miiller  the  falsetto  notes  were  thought  to  be  due  to  vibrations  of 
only  the  inner  borders  of  the  vocal  cords.  In  the  opinion  of  Petrequin 
and  Diday;»  they  do  not  result  from  vibrations  of  the  vocal  cords  at  all, 
but  from  vibrations  of  the  air  passing  through  the  aperture  of  the  glottis, 
which  they  believe  assumes,  at  such  times,  the  contour  of  the  embouchure 
of  a  flute.  Others  {considering  some  degree  of  similarity  which  exists 
between  the  falsetto  notes  and  the  peculiar  tones  called  harmonic,  which 
are  produced  when,  by  touching  or  stopping  a  harp-string  at  a  particular 
point,  only  a  portion  of  its  length  is  allowed  to  vibrate)  have  supposed 
that,  in  the  falsetto  notes,  portions  of  the  vocal  ligaments  are  thus  iso- 
lated, and  made  to  vibrate  while  the  rest  are  held  still.  The  question 
cannot  yet  be  settled;  but  any  one  in  the  habit  of  singing  may  assure 
himself,  both  by  the  difficulty  of  passing  smoothly  from  one  set  of  notes 
to  the  other,  and  by  the  necessity  of  exercising  himself  in  both  registers, 
lest  he  should  become  very  deficient  in  one,  that  there  must  be  some 
great  difference  in  the  modes  in  which  their  respective  notes  are  produced. 

The  strength  of  the  voice  depends  partly  on  the  degree  to  which  the 
vocal  cords  can  be  made  to  vibrate;  and  partly  on  the  fitness  for  reso- 
nance of  the  membranes  and  cartilages  of  the  larynx,  of  the  parietes  of  the 
thorax,  lungs,  and  cavities  of  the  mouth,  nostrils,  and  communicating 
sinuses.  It  is  diminished  by  anything  which  interferes  with  such 
capability  of  vibration.  The  intensity  or  loudness  of  a  given  note  with 
maintenance  of  the  same  "pitch,"^  cannot  be  rendered  greater  by  merely 
increasing  the  force  of  the  current  of  air  through  the  glottis;  for  increase 
of  the  force  of  the  current  of  air,  cmteris  paribus,  raises  the  pitch  both  of 
the  natural  and  the  falsetto  notes.  Yet,  since  a  singer  possesses  the 
power  of  increasing  the  loudness  of  a  note  from  the  faintest  "piano^^  to 
"fortissimo^"  without  its  pitch  being  altered,  there  must  be  some  means 
of  compensating  the  tendency  of  the  vocal  cords  to  emit  a  higher  note 
when  the  force  of  the  current  of  air  is  increased.  This  means  evidently 
consists  in  modifying  the  tension  of  the  vocal  cords.  When  a  note  is 
rendered  louder  and  more  intense,  the  vocal  cords  must  be  relaxed  by 
remission  of  the  muscular  action,  in  proportion  as  the  force  of  the  current 
of  the  breath  through  the  glottis  is  increased.  When  a  note  is  rendered 
fainter,  the  reverse  of  this  must  occur. 

The  arches  of  the  palate  and  the  uvula  become  contracted  during  the 
formation  of  the  higher  notes;  but  their  contraction  is  the  same  for  a 
note  of  given  height,  whether  it  be  falsetto  or  not;  and  in  either  case  the 
arches  of  the  palate  may  be  touched  with  the  finger,  without  the  note 
being  altered.  Their  action,  therefore,  in  the  production  of  the  higher 
notes  seems  to  be  merely  the  result  of  involuntary  associate  nervous 
action,  excited  by  the  voluntarily  increased  exertion  of  the  muscles  of  the 


60 


HAND-BOOK  OF  PHYSIOLOGY. 


larynx.  If  the  palatine  arches  contribute  at  all  to  the  production  of 
the  higher  notes  of  the  natural  voice  and  the  falsetto,  it  can  only  be  by 
their  increased  tension  strengthening  the  resonance. 

The  office  of  the  ventricles  of  the  larynx  is  evidently  to  afford  a  free 
space  for  the  vibrations  of  the  lips  of  the  glottis;  they  may  be  compared 
with  the  cavity  at  the  commencement  of  the  mouth-piece  of  trumpets, 
which  allows  the  free  vibration  of  the  lips. 

Speech. 

Besides  the  musical  tones  formed  in  the  larynx,  a  great  number  of 
other  sounds  can  be  produced  in  the  vocal  tubes,  between  the  glottis  and 
the  external  apertures  of  the  air-passages,  the  combination  of  which  sounds 
by  the  agency  of  the  cerebrum  into  different  groups  to  designate  objects, 
properties,  actions,  etc.,  constitutes  language.  The  languages  do  not 
employ  all  the  sounds  which  can  be  produced  in  this  manner,  the  com- 
bination of  some  with  others  being  often  difficult.  Those  sounds  which 
are  easy  of  combination  enter,  for  the  most  part,  into  the  formation  of 
the  greater  number  of  languages.  Each  language  contains  a  certain 
number  of  such  sounds,  but  in  no  one  are  all  brought  together.  On  the 
contrary,  different  languages  are  characterized  by  the  prevalence  in  them 
of  certain  classes  of  these  sounds,  while  others  are  less  frequent  or  alto- 
gether absent. 

Articulate  Sounds. — The  sounds  produced  in  speech,  or  articulate 
sounds,  are  commonly  divided  into  voivels  and  c07isonants:  the  distinction 
between  which  is,  that  the  sounds  for  the  former  are  generated  by  the 
larynx,  while  those  for  the  latter  are  produced  by  interruption  of  the  cur- 
rent of  air  in  some  part  of  the  air-passages  above  the  larynx.  The  term 
consonant  has  been  given  to  these  because  several  of  them  are  not  prop- 
erly sounded,  except  consonantly  with  a  vowel.  Thus,  if  it  be  attempted 
to  pronounce  aloud  the  consonants  h,  d,  and  g,  or  their  modifications,  p, 
t,  h,  the  intonation  only  follows  them  in  their  combination  with  a  vowel. 
To  recognize  the  essential  properties  of  the  articulate  sounds,  we  must, 
according  to  Miiller,  first  examine  them  as  they  are  produced  in  whisper- 
ing, and  then  investigate  which  of  them  can  also  be  uttered  in  a  modified 
character  conjoined  with  vocal  tone.  By  this  procedure  we  find  two 
series  of  sounds:  in  one  the  sounds  are  mute,  and  cannot  be  uttered  with 
a  vocal  tone;  the  sounds  of  the  other  series  can  be  formed  independently 
of  voice,  but  are  also  capable  of  being  uttered  in  conjunction  with  it. 

All  the  vowels  can  be  expressed  in  a  whisper  without  vocal  tone,  that 
is,  mutely.  Tliesc  mute  vowel-sounds  differ,  however,  in  some  measure, 
as  to  their  mode  of  production,  from  the  consonants.  All  the  mute  con- 
soTiants  are  formed  in  the  vocal  tube  above  tlie  glottis,  or  in  the  cavity  of 
the  mouth  or  nose,  by  tlie  mere  rushing  of  the  ;iir  between  the  surfaces 


THE  VOICE  AND  SPEECH. 


61 


differently  modified  in  disposition.  But  the  sound  of  the  vowels,  even 
when  mute,  has  its  source  in  the  glottis,  though  its  vocal  cords  are  not 
thrown  into  the  vibrations  necessary  for  the  production  of  voice;  and  the 
sound  seems  to  be  produced  by  the  passage  of  the  current  of  air  between 
the  relaxed  vocal  cords.  The  same  vowel  sound  can  be  produced  in  the 
larynx  when  the  mouth  is  closed,  the  nostrils  being  open,  and  the  utter- 
ance of  all  vocal  tone  avoided.  This  sound,  when  the  mouth  is  open,  is 
so  modified  by  varied  forms  of  the  oral  cavity,  as  to  assume  the  characters 
of  the  vowels  a,  e,  ^,  o,  u,  in  all  their  modifications. 

The  cavity  of  the  mouth  assumes  the  same  form  for  the  articulation 
of  each  of  the  mute  vowels  as  for  the  corresponding  vowel  when  vocal- 
ized; the  only  difference  in  the  two  cases  lies  in  the  kind  of  sound  emitted 
by  the  larynx.  Krantzenstein  and  Kempelen  have  pointed  out  that  the 
conditions  necessary  for  changing  one  and  the  same  sound  into  the  differ- 
ent vowels,  are  differences  in  the  size  of  two  parts — the  oral  xjanal  and 
the  oral  opening;  and  the  same  is  the  case  with  regard  to  the  mute  vowels. 
By  oral  canal,  Kempelen  means  here  the  space  between  the  tongue  and 
palate:  for  the  pronunciation  of  certain  vowels  both  the  opening  of  the 
mouth  and  the  space  just  mentioned  are  widened;  for  the  pronunciation 
of  other  vowels  both  are  contracted;  and  for  others  one  is  wide,  the  other 
contracted.  Admitting  five  degrees  of  size,  both  of  the  opening  of  the 
mouth  and  of  the  space  between  the  tongue  and  palate,  Kempelen  thus 
states  the  dimensions  of  these  parts  for  the  following  vowel  sounds: — 


Vow^l.        Sound.  Size  of  oral  opening.  Size  of  oral  canal. 

a    as  in  "far"  5  ...  3 

a       "    ^'name"  4  ...  2 

e       "   '^theme''  3  ...  1 

0       "   "go''  2  ...  4 

00      "   "cool''  1  ...  5 


Another  important  distinction  in  articulate  sounds  is,  that  the  utter- 
ance of  some  IS  only  of  momentary  duration,  taking  place  during  a  sud- 
den change  in  the  conformation  of  the  mouth,  and  being  incapable  of 
prolongation  by  a  continued  expiration.  To  this  class  belong  ^,  d,  and 
the  hard  g.  In  the  utterance  of  other  consonants  the  sounds  may  be 
conti7iuous;  they  may  be  prolonged,  ad  libitum,  as  long  as  a  particular 
disposition  of  the  mouth  and  a  constant  expiration  are  maintained. 
Among  these  consonants  are  h,  m,  n,  f,  s,  r,  I.  Corresponding  differ- 
ences in  respect  to  the  time  that  may  be  occupied  in  their  utterance  exist 
in  the  vowel  sounds,  and  principally  constitute  the  differences  of  long  and 
short  syllables.  Thus  the  a  as  in  "far"  and  "fate,"  the  o  as  in  "go"  and 
"fort,"  may  be  indefinitely  prolonged;  but  the  same  vowels  (or  more 
properly  different  vowels  expressed  by  the  same  letters),  as  in  "can" 
and  "fact,"  in  "dog"  and  "rotten,"  cannot  be  prolonged. 


62  HAND-BOOK  OF  PHYSIOLOGY. 

All  sounds  of  the  first  or  explosive  kind  are  insusceptible  of  combina- 
tion with  vocal  tone  ("intonation"),  and  are  absolutely  mute;  nearly  all 
the  consonants  of  the  second  or  continuous  kind  may  be  attended  with 
"intonation/^ 

Ventriloquism. — The  peculiarity  of  speaking,  to  which  the  term 
ventriloquism  is  applied,  appears  to  consist  merely  in  the  varied  modifi- 
cation of  the  sounds  produced  in  the  larynx,  in  imitation  of  the  modifica- 
tions which  voice  ordinarily  suffers  from  distance,  etc.  From  the  obser- 
vations of  Miiller  and  Colombat,  it  seems  that  the  essential  mechanical 
parts  of  the  process  of  ventriloquism  consist  in  taking  a  full  inspiration, 
then  keeping  the  muscles  of  the  chest  and  neck  fixed,  and  speaking  with 
the  mouth  almost  closed,  and  the  lips  and  lower  jaw  as  motionless  as 
possible,  while  air  is  very  slowly  expired  through  a  very  narrow  glottis; 
care  being  taken  also,  that  none  of  the  expired  air  passes  through  the 
nose.  But,  as  observed  by  Miiller,  much  of  the  ventriloquist's  skill  in 
imitating  the  voices  coming  from  particular  directions,  consists  in  deceiv- 
ing other  senses  than  hearing.  We  never  distinguish  very  readily  the 
direction  in  which  sounds  reach  our  ear;  and,  when  our  attention  is 
directed  to  a  particular  point,  our  imagination  is  very  apt  to  refer  to  that 
point  whatever  sounds  we  may  hear. 

Action  of  the  Tojigue  in  Speech. — The  tongue,  which  is  usually 
credited  with  the  power  of  speech — language  and  speech  being  often 
employed  as  synonymous  terms — plays  only  a  subordinate,  although  very 
important  part.  This  is  well  shown  by  cases  in  which  nearly  the  whole 
organ  has  been  removed  on  account  of  disease.  Patients  who  recover 
from  this  operation  talk  imperfectly,  and  their  voice  is  considerably  mod- 
ified; but  the  loss  of  speech  is  confined  to  those  letters  in  the  pronuncia- 
tion of  which  the  tongue  is  concerned. 

Stammering  depends  on  a  want  of  harmony  between  the  action  of 
the  muscles  (chiefly  abdominal)  which  expel  air  through  the  larynx,  and 
that  of  the  muscles  which  guard  the  orifice  (rima  glottidis)  by  which  it 
escapes,  and  of  those  (of  tongue,  palate,  etc.)  which  modulate  the  sound 
to  the  form  of  speech. 

Over  either  of  the  groups  of  muscles,  by  itself,  a  stammerer  may  have 
as  much  power  as  other  people.  But  he  cannot  harmoniously  arrange 
their  conjoint  actions. 


CHAPTEE  XVII. 


NUTRITION;   THE  INCOME  AND  EXPENDITURE  OF  THE  HUMAN 

BODY. 

The  various  physiological  processes  which  occur  in  the  human  body- 
have,  with  the  exception  of  those  in  the  nervous  and  generative  systems, 
which  will  be  considered  in  succeeding  chapters,  now  been  dealt  with, 
and  it  will  be  as  well  to  give  in  this  chapter  on  Nutrition  a  summary  of 
what  has  been  considered  more  at  length  before. 

The  subject  may  be  considered  under  the  following  heads.  (1).  The 
Evidence  and  Amount  of  Expenditure.  (2).  The  Sources  and  Amount 
of  Income.    (3).  The  Sources  and  Objects  of  Expenditure. 

1.  Evidence  and  Amount  of  Expenditure. — The  evidence  of 
Expenditure  by  the  living  body  is  abundantly  complete. 

From  the  table  (p.  212,  Vol.  I.)  it  will  be  seen  how  the  various  amounts 
of  the  excreta  are  calculated. 

From  theLungs  there  is  exhaled  every  24  hours. 

Of  Carbonic  Acid,  about     ....    15,000  grains 
"  Water    .       .       .       .  •    .       .       .     5,000  " 
Traces  of  organic  matter. 

From  the  Shin — 

Water   11,500  grains 

Solid  and  gaseous  matter    ....        250  " 

From  the  Kidneys — 

Water        .......  23,000  grains 

Organic  matter  ......  680 

Minerals  or  salines   420 

From  the  Intestines — 

Water   2,000  grains 

Various  organic  and  mineral  substances      .  800 

In  the  account  of  Expenditure,  must  be  remembered  in  addition  the 
milk  (during  the  period  of  suckling),  and  the  products  of  secretion  from 
the  generative  organs  (ova,  menstrual  blood,  semen);  but,  from  their 
variable  and  uncertain  amounts,  these  cannot  be  reckoned  with  the  pre- 
ceding. 


64 


HAND-BOOK  OF  PHYSIOLOGY. 


Altogether,  the  Expenditure  Of  the  body  represented  by  the  sum  of 
these  various  excretory  products  amounts  every  24  hours  to — 

Solid  and  gaseous  matter    .       .       .    17,150  grains  (1,113  grms.) 
Water  (either  fluid  or  combined  with 

the  solids  and  gaseous  matter).        .    49,500     "     (2,695    "  ) 

The  matter  thus  lost  by  the  body  is  matter  the  chemical  attractions  of 
which  have  been  in  great  part  satisfied;  and  Avhich  remains  quite  useless 
as  food,  until  its  elements  have  been  again  separated  and  re-arranged  by 
members  of  the  vegetable  world  (p.  2,  Vol.  I.).  It  is  especially  instructive 
to  compare  the  chemical  constitution  of  the  products  of  expenditure,  thus 
separated  by  the  various  excretory  organs,  with  that  of  the  sources  of  in- 
come to  be  immediately  considered. 

It  is  evident  from  these  facts  that  if  the  human  body  is  to  maintain 
its  size  and  composition,  there  must  be  added  to  it  matter  corresponding 
in  amount  with  that  which  is  lost.  The  income  must  equal  the  expen- 
diture. 

2.  Sources  and  Amount  of  Income. — The  Income  of  the  body 
consists  partly  of  Food  and  DrinTc,  and  partly  of  Oxygen. 
Into  the  stomach  there  is  received  daily: — 

Solid  (chemically  dry)  food        ,       .  8,000  grains  (520  grms.) 

Water  (as  water,  or  variously  com- 
bined with  solid  food)      .       .       .  35,000-40,000        (2,444  ) 

By  the  lungs  there  is  absorbed  daily: — 

Oxygen       .....  13,000    "      844  ) 

The  average  total  daily  receipts,  in  the  shape  of  food,  drink  and  oxy- 
gen, correspond,  therefore,  with  the  average  total  daily  expenditure,  as 
shown  by  the  following  table: 


I'iXCOTHjBm 

Solid  food        .       .    8,000  grains 
Water      .       .       .  37,650 
Oxygen    .       .       .  13,000  " 

58,650  grains 
(about  3,808  grms.,  or  8^  lb.) 


Expenditure. 
Lungs     .       .       .  20,000  grains. 
Skin       .       .       .  11,750 
Kidneys  .       .       .24,100  " 
Intestines       .       .2,800  " 
(Generative  and  mam- 
mary-gland products 
are  supposed  to  be  in- 
cluded.) 


58,650  grains 
(About  3,808  grms.) 

These  quantities  are  approximate  only.  But  they  may  be  taken  as 
fair  averages  for  a  healthy  adult.    The  absolute  identity  of  the  two 


INCOME  AND  EXPENDITURE  OF  BODY. 


65 


numbers  (in  grains)  in  the  two  tables  is  of  course  diagrammatic.  No  such 
exactitude  in  the  account  occurs  in  any  living  body,  in  the  course  of  any 
given  twenty-four  hours.  But  any  difference  which  exists  between  the 
two  amounts  of  income  and  expenditure  at  any  given  period,  corresponds 
merely  with  the  slight  variations,  in  the  amount  of  capital  (weight  of 
body),  to  which  the  healthiest  subject  is  liable. 

The  chemical  composition  of  the  food  (p.  213,  Vol.1.)  may  be  profitably 
compared  with  that  of  the  excreta,  as  before  mentioned.  The  greater  part 
of  our  food  is  composed  of  matter,  which  contains  much  potential  energy; 
and  in  the  chemical  changes  (combustion  and  other  processes),  to  which 
it  is  subject  in  the  body,  active  energy  is  manifested. 

3.  The  Sources  and  Objects  of  Expenditure. — The  sources  of 
necessary  waste  and  expenditure  in  the  living  body  are  various  and  ex- 
tensive. They  may  be  comprehended  under  the  following  heads: — (1) 
Common  loear  and  tear;  such  as  that  to  which  all  structures,  living  and 
not  living,  are  subjected  by  exposure  and  work;  but  which  must  be 
especially  large  in  the  soft  and  easily  decaying  structures  of  an  animal 
body. 

(2)  Manifestations  of  Force  in  the  form  either  of  Heat  or  Motion.  In 
the  former  case  (Heat),  the  combustion  must  be  sufficient  to  maintain 
a  temperature  of  about  100^  F.  (37*8°  C.)  throughout  the  whole  sub- 
stance of  the  body,  in  all  varieties  of  external  temperature,  notwithstand- 
ing the  large  amount  continually  lost  in  the  ways  previously  enumerated 
(p.  313,  Vol.  I.).  In  the  case  of  Motion,  there  is  the  expenditure  involved 
in  {a)  Ordinary  muscular  movements,  as  in  Prehension,  Mastication,  Lo- 
comotion, and  numberless  other  ways:  {h)  Various  involuntary  movements, 
as  in  Eespiration,  Circulation,  Digestion,  etc. 

(3)  Manifestation  of  Nerveforce;  as  in  the  general  regulation  of  all 
physiological  processes,  e.g.,  Respiration,  Circulation,  Digestion;  and  in 
Volition  and  all  other  manifestations  of  cerebral  activity. 

(4)  The  energy  expended  in  all  physiological  processes ,  e.g.,  Nutrition, 
Secretion,  Growth,  and  the  like. 

The  Total  expenditure  or  manifestation  of  energy  by  an  animal  body 
can  be  measured,  with  fair  accuracy;  the  terms  used  being  such  as  are 
employed  in  connection  with  other  than  vital  operations.  All  statements 
however,  must  be  considered  for  the  present  approximate  only,  and  es- 
pecially is  this  the  case  with  respect  to  the  comparative  share  of  expendi- 
ture to  be  assigned  to  the  various  objects  just  enumerated. 

The  amount  of  energy  daily  manifested  by  the  adult  human  body  in. 
(a)  the  maintenance  of  its  temperature;  {V)  in  internal  mechanical  work, 
as  in  the  movements  of  the  respiratory  muscles,  the  heart,  etc. ;  and  [c]  in 
external  mechanical  work,  as  in  locomotion  and  all  other  voluntary  move- 
ments, has  been  reckoned  at  about  3,400  foot-tons  (p.  124,  Vol.  I.).  Of  this 
amount  only  one-tenth  is  directly  expended  in  internal  and  external 
Vol.  II.— 5. 


66 


HAND-BOOK  OF  PHYSIOLOGY. 


mechanical  work;  the  remainder  being  employed  in  the  maintenance  of 
the  body^s  heat.  The  latter  amount  represents  the  heat  which  would  be 
required  to  raise  48 '4  lb.  of  water  from  the  freezing  to  the  boiling  point; 
or  if  converted  into  mechanical  power,  it  would  suffice  to  raise  the  body 
of  a  man  weighing  about  150  lb.  through  a  vertical  height  of  8J  miles. 

To  the  foregoing  amounts  of  expenditure  must  be  added  the  quite  un- 
known quantity  expended  in  the  various  manifestations  of  nerve-force,  and 
in  the  work  of  nutrition  and  growth  (using  these  terms  in  their  widest 
sense).  By  comparing  the  amount  of  energy  which  should  be  produced 
in  the  body  from  so  much  food  of  a  given  kind,  with  that  which  is  actu- 
ally manifested  (as  shown  by  the  various  products  of  combustion,  in  the 
excretions)  attempts  have  been  made,  indeed,  to  estimate,  by  a  process  of 
exclusion,  these  unknown  quantities;  but  all  such  calculations  must  be  at 
present  considered  only  very  doubtfully  approximate. 

Sources  of  Error. — Among  the  sources  of  error  in  any  such  calcu- 
lations must  be  reckoned,  as  a  chief  one,  the,  at  present,  entirely  unknown 
extent  to  which  forces  external  to  the  body  (mainly  heat)  can  be  utilized 
by  the  tissues.  We  are  too  apt  to  think  that  the  heat  and  light  of  the  sun 
are  directly  correlated,  as  far  as  living  beings  are  concerned,  with  the 
chemico -vital  transformations  involved  in  the  nutrition  and  growth  of  the 
members  of  the  vegetable  world  only.  But  animals,  although  compara- 
tively independent  of  external  heat  and  other  forces,  probably  utilize 
them,  to  the  degree  occasion  offers.  And  although  the  correlative  manifes- 
tation of  energy  in  the  body,  due  to  external  heat  and  light,  may  still  be 
measured  in  so  far  as  it  may  take  the  form  of  mechanical  work;  yet,  in 
so  far  as  it  takes  the  form  of  expenditure  in  nutrition  or  nerve-force,  it  is 
evidently  impossible  to  include  it  by  any  method  of  estimation  yet  dis- 
covered; and  all  accounts  of  it  must  be  matters  of  the  purest  theory. 
These  considerations  may  help  to  explain  the  apparent  discrepancy  be- 
tween the  amount  of  energy  which  is  capable  of  being  produced  by  the 
usual  daily  amount  of  food,  with  that  which  is  actually  manifested  daily 
by  the  body;  the  former  leaving  but  a  small  margin  for  anything  beyond 
the  maintenance  of  heat,  and  mechanical  work. 

In  the  foregoing  sketch  we  have  supposed  that  the  excreta  are  exactly 
replaced  by  the  ingesta. 

NiTROGEN-Qus  Equilibrium  and  Formation  of  Fat. 

If  an  animal,  which  has  undergone  a  starving  period,  be  fed  upon  a 
diet  of  lean  meat,  it  is  found  tliat  instead  of  the  greater  part  of  the  nitro- 
gen being  stored  up,  as  one  would  expect,  the  chief  part  of  it  ai)pears  in 
the  urine  as  urea,  and  on  continuing  with  the  diet  the  excreted  nitrogen 
approximates  more  and  more  closely  to  the  ingested  nitrogen  until  at  last 
the  amounts  are  equal  in  both  cases.    This  is  called  uitrogoious  cquiJi- 


INCOME  AND  EXPENDITURE  OF  BODY. 


67 


Irium.  There  may,  however,  be  at  the  same  time  an  increase  Of  weight 
which  is  due  to  the  putting  on  of  fat.  If  this  is  the  case  it  must  be  ap- 
parent that  the  protoplasm  of  the  tissues  is  able  to  form  fat  out  of  proteid 
material  and  to  split  it  up  into  urea  and  fat.  If  fat  be  given  in  small 
quantities  with  the  meat,  for  a  time  the  carbon  of  the  egesta  and  in- 
gesta  are  equal,  but  if  the  fat  be  increased  beyond  a  certain  point  the 
body  weight  increases  from  a  deposition  of  fat;  not,  however,  by  a 
mere  mechanical  deposition  or  filtration  from  the  blood,  but  by  an  actual 
act  of  secretion  by  the  protoplasm  whereby  the  fat  globules  are  stored' 
up  within  itself.  In  a  similar  manner  as  regards  carbo-hydrates,  if  they 
are  in  small  quantity,  the  whole  of  the  carbon  appears  in  the  excreta,  but 
beyond  a  certain  amount  a  considerable  portion  of  it  is  retained  in  fat, 
having  been  by  the  protoplasm  stored  up  within  itself  in  that  material.- 
The  amount  of  proteid  material  required  to  produce  nitrogenous  equi- 
librium is  considerable,  but  it  may  be  materially  diminished  by  the  addition 
of  carbo-hydrate  or  fatty  food  or  of  gelatine  to  the  exclusively  meat  diet. 

It  is  of  much  interest  to  consider  how  the  protoplasm  acts  in  convert- 
ing food  into  energy  and  decomposition  products,  since  the  substance 
itself  does  not  undergo  much  change  in  the  process  except  a  slight  amount 
of  wear  and  tear.  We  may  assume  that  it  is  the  property  of  protoplasm 
to  separate  from  the  blood  the  materials  which  may  be  required  to  pro- 
duce secretions,  in  the  case  of  the  protoplasm  of  secreting  glands,  or  to 
evolve  heat  and  energy,  as  in  the  case  of  the  protoplasm  of  muscle.  The 
substances  are  very  possibly  different  for  each  process,  and  the  decomposi- 
tion products,  too,  may  be  different  in  quality  or  quantity.  Proteid  ma- 
terials appear  to  be  specially  needed,  as  is  shown  by  the  invariable  pres- 
ence of  urea  in  the  urine  even  during  starvation;  and  as  in  the  latter  case, 
there  has  been  no  food  from  which  these  materials  could  have  been  derived, 
the  urea  is  considered  to  be  derived  from  the  disintegration  of  the  nitrog- 
enous tissues  themselves.  The  removal  of  all  fat  from  the  body  in  a  star- 
vation period,  as  the  first  apparent  change,  would  lead  to  the  supposition 
that  fat  is  also  a  specially  necessary  pabulum  for  the  production  of  proto- 
plasmic energy;  and  the  fact  that,  as  mentioned  above,  with  a  diet  of 
lean  meat  an  enormous  amount  appears  to  be  required,  suggests  that  in  that 
case  protoplasm  obtains  the  fat  it  needs  from  the  proteid  food,  which  pro- 
cess must  be  evidently  a  source  of  much  waste  of  nitrogen.  The  idea 
that  proteid  food  has  two  destinations  in  the  economy,  viz.,  to  form  organ 
or  tissue  proteid  which  builds  up  organs  and  tissues,  and  circulating  pro- 
teid, from  which  the  organs  and  tissues  derive  the  materials  of  their  secre- 
tions or  for  producing  their  energy,  is  a  convenient  one,  as  it  is  unlikely 
that  protoplasm  would  go  to  the  expense  of  construction  simply  for  the 
sake  of  immediate  destruction. 


CHAPTER  XVIII. 


THE  NERVOUS  SYSTEM. 

Chief  Divisions  of  the  Nervous  System. — The  Nervous  System 
consists  of  two  portions  or  systems,  the  (I.)  Cerebrospinal,  and  the  (II.) 

Sympathetic. 

(I.)  The  Cerehro-spinal  system  includes  the  Brain  and  Spinal  cord, 
with  the  nerves  proceeding  from  them.  Its  fibres  are  chiefly,  but  not 
exclusively,  distributed  to  the  skin  and  other  organs  of  the  senses,  and  to 
the  voluntary  muscles. 

(II.)  The  Sympathetic  Nervous  system  consists  of: — (1)  A  double  chain 
of  ganglia  and  fibres,  which  extends  from  the  cranium  to  the  pelvis,  along 
each  side  of  the  vertebral  column,  and  from  which  branches  are  distributed 
both  to  the  cerebro-spinal  system  and  to  other  parts  of  the  sympathetic 
system.  With  these  may  be  included  the  small  ganglia  in  connection  with 
those  branches  of  the  fifth  cerebral  nerve  which  are  distributed  in  the 
neighborhood  of  the  organs  of  special  sense:  namely,  the  ophthalmic,  otic, 
spheno-palatine,  and  submaxillary  ganglia.  (2)  Various  ganglia  and 
plexuses  of  nerve-fibres  which  give  olf  branches  to  the  thoracic  and  ab- 
dominal viscera,  the  chief  of  such  plexuses  being  the  Cardiac,  Solar,  and 
Hypogastric;  but  in  intimate  connection  with  these  are  many  secondary 
plexuses,  as  the  aortic,  spermatic,  and  renal.  To  these  plexuses,  fibres 
pass  from  the  prsevertebral  chain  of  ganglia,  as  well  as  from  cerebro-spinal 
nerves.  (3)  Various  ganglia  and  plexuses  in  the  substance  of  many  of 
the  viscera,  as  in  the  stomach,  intestines,  and  urinary  bladder.  These, 
which  are,  for  the  most  part,  microscopic,  also  freely  communicate  with 
other  parts  of  the  sympathetic  system,  as  well  as,  to  some  extent,  with  tlie 
cerebro-spinal.  (4)  By  many,  the  ganglia  on  the  posterior  roots  of  the 
spinal  nerves,  on  the  glosso-pharyngeal  and  vagus,  and  on  the  sensory  root 
of  fifth  cerebral  nerve  (Gasserian  ganglion),  are  also  included  as  sym- 
pathetic-nerve structures. 

Elementary  Structure. — The  organs  both  of  the  Cerebro-spinal  and 
Sympathetic  nervous  systems  are  composed  of  two  structural  elonients 
—fibres  and  cells.  The  cells  are  collected  in  masses,  and  are  always  min- 
gled, more  or  less,  with  fibres;  such  a  collection  of  cellular  and  fibrous 
nerve-structure  being  termed  a  nerve-centre.  The  fibres,  besides  entering 
into  the  composition  of  nerve-centres,  form  by  themselves  the  nerves. 


THE  NERVOUS  SYSTEM. 


69 


which  connect  the  various  centres,  and  are  distributed  in  the  several  parts 
of  the  body. 

Nerve  Fibres. 

Structure. — Each  nerve-trunk  is  composed  of  a  variable  number  of 
different-sized  bundles  (funiculi)  of  nerve-fibres  which  have  a  special 
sheath  [perineurium  ox  neurilemma).    The  funiculi  are  enclosed  in  a  firm 


Fia.  302.— Transverse  section  of  the  sciatic  nerve  of  a  cat  x  100.— It  consists  of  bundles  {Funiculi) 
of  nerve-fibres  ensheathed  in  a  fibrous  supporting  capsule,  epineurium,  A ;  each  bundle  has  a  special 
sheath  (not  sufficiently  worked  out  from  the  epineurium  in  the  figure)  or  perineurium  B ;  the  nerve- 
fibres  N/ are  separated  from  one  another  by  endoneurium;  L,  lymph  spaces;  Ar,  artery;  V,  vein; 
F,  fat.  (V.D.Harris.) 

fibrous  sheath  (epineurium) ;  this  sheath  also  sends  in  processes  of  connec- 
tive tissue  which  connect  the  bundles  together.  In  the  funiculi  between 
the  fibres  is  a  delicate  supporting  tissue  (the  endoneurium). 

There  are  numerous  lymph-spaces  both  beneath  the  connective  tissue 
investing  individual  nerve-  fibres,  and  also  beneath  that  which  surrounds 
the  funiculi. 

Varieties. — In  most  nerves,  two  kinds  of  fibres  are  mingled;  those 
of  one  kind  being  most  numerous  in,  and  characteristic  of,  nerves  of  the 
Cerebro-spinal  system;  those  of  the  other,  most  numerous  in  nerves  of  the 
Sympathetic  system.  These  are  called  (a)  medullated  or  white  fibres, 
and  (b)  non-medullated  or  grey  fibres. 

(a)  Medullated  Fibres. — Each  medullated  nerve-fibre  is  made  up 
of  the  following  parts: — (1.)  Primitive  nerve  sheath,  or  nucleated  sheath 
of  Schwann.  (2)  Medullary  sheath,  or  white  substance  of  Schwann. 
(3)  Axis -cylinder,  primitive  band,  axis  band,  or  axial  fibre. 

Although  these  parts  can  be  made  out  in  nerves  examined  some  time 
after  death,  in  a  recent  specimen  the  contents  of  the  sheath  appear  to  be 
homogeneous.  But  by  degrees  they  undergo  changes  which  show  them 
to  be  composed  of  two  different  materials.    The  internal  or  central  part, 


70 


IIa\ND-BOOK  OF  PHYSIOLOGY. 


occupying  the  axis  of  the  tube  {axis-cylinder),  becomes  greyish,  while 
the  outer,  or  cortical  portion  [white  siihstance  of  Schwann),  becomes  opaque 
and  dimly  granular  or  grumous,  as  if  from  a  kind  of  coagulation.  At  the 
same  time,  the  fine  outline  of  the  previously  transparent  cylindrical  tube 
is  exchanged  for  a  da^v  double  contour  (Fig.  303,  b),  the  outer  line  being 
formed  b}^  the  sheath  of  the  fibre,  the  inner  by  the  margin  of  curdled  or 
coagulated  medullary  substance.  The  granular  material  shortly  collects 
into  little  masses,  which  distend  portions  of  the  tubular  membrane;  while 
the  intermediate  spaces  collapse,  giving  the  fibres  a  varicose,  or  beaded 
appearance  (Fig.  303,  c  and  d),  instead  of  the  previous  cylindrical  form. 


Fig.  303.  Fig.  304. 

Fig.  303.— Primitive  nerve-fibres,  a.  A  perfectly  fresh  tubule  with  a  single  dark  outline,  b.  A 
tubule  or  fibre  with  a  double  contom*  from  commencing  post-mortem  change,  c.  The  changes 
f  m-ther  advanced,  producing  a  varicose  or  beaded  appearance,  d.  A  tubule  or  fibre,  the  central  part 
of  wliich,  in  consequence  of  still  f  m-ther  changes,  has  accumulated  in  sepaa'ate  portions  within  the 
sheath.  (Wagner.) 

Fig.  304.— Two  nerve-fibres  of  sciatic  nerve,  a.  Node  of  Ranvier.  b.  Axis-cyUnders.  c.  Sheath 
of  Schwann,  with  nuclei.   X  300.  (Klein  and  Noble  Smith.) 

The  whole  contents  of  the  nerve-tubules  are  extremely  soft,  for  when  sub- 
jected to  pressure  they  readily  pass  from  one  part  of  the  tubular  sheath  to 
another,  and  often  cause  a  bulging  at  the  side  of  the  membrane.  They 
also  readily  escape,  on  pressure,  from  the  extremities  of  the  tubule,  in  the 
form  of  a  grumous  or  granular  material. 

The  nucleated  sheath  of  Sch  wann  is  a  pellucid  membrane,  forming  the 
outer  investment  of  the  nerve-fibre.  Within  this  delicate  structureless 
membrane  nuclei  are  seen  at  intervals,  surrounded  by  a  variable  amount 
of  protoplasm.  The  sheath  is  structureless,  like  tlio  sarcolemma,  and  the 
nuclei  appear  to  be  within  it:  together  witli  the  protoplasm  wliich  sur- 
rounds tliem,  they  are  tlie  relics  of  embryonic  cells,  and  from  their  resem- 
blance to  the  muscle  corpuscles  of  striated  muscle,  may  be  termed  nerve- 
corpuscles. 


THE  NERVOUS  SYSTEM. 


71 


According  to  McCarthy,  the  medullary  sheath J}s  cori^osed  of 


material. 


(2.)  The  mMlullary  sheath  or  white  substance  of  Schwann  is  the  part 
to  which  the  peculiar  white  aspect  of  the  cerebro -spinal  nerves  is  princi- 
pally due.  It  is  a  thick,  fatty,  semi-fluid  substance,  as  we  have  seen,  pos- 
sessing a  double  contour.  It  is  said  to  be  made  up^^?^^^S§S*3?^ticulum 
(Stilling,  Klein),  in  the  meshes  of  which  is  embe^i^d  the  ]^;i|^l&v^ty 

rods  radiating  from  the  axis-cylinder  to  the  sheathVot  Schwann.  Some- 
times the  whole  space  is  occupied  by  these  rods,  whJjkfc  ^t  other  times  tk^ 
rods  appear  shortened,  and  compressed  laterally  into  Diindles  embe^dgd  in 
some  homogeneous  substance.  '"^v  q  ^  ^ 

(3.)  The  axis-ci^linder  consists  of  a  large  number  of  pr!lfebit?ve /^n7/^ 
This  is  well  shown  in  the  cornea,  where  the  axis-cylinders  of  riei 
up  into  minute  fibrils  which  go  to  form  terminal  networks  (see  Cornea), 
and  also  in  the  spinal  cord,  where  these  fibrillse  form  a  large  part  of  tlie 
grey  matter.  From  various  considerations  such  as  its 
invariable  presence  and  unbroken  continuity  in  all 
nerves,  though  the  primitive  sheath  or  the  medullary 
sheath  may  be  absent,  there  can  be  little  doubt  that 
the  axis-cylinder  is  the  conductor  of  nerve-force,  the 
other  parts  of  the  nerve  having  the  subsidiary  function 
of  support  and  possibly  of  insulation. 

At  regular  intervals  in  most  medullated  nerves,  the 
nucleated  sheath  of  Schwann  possesses  annular  con- 
strictions (nodes  of  Eanvier).  At  these  points  (Figs. 
304,  305),  the  continuity  of  the  medullary  white  sub- 
stance is  interrupted,  and  the  primitive  sheath  comes 
into  immediate  contact  with  the  axis-cylinder. 

Size.— The  size  of  the  nerve-fibres  varies,  and  the 
same  fibres  do  not  preserve  the  same  diameter  through 
their  whole  length,  being  largest  in  their  course  within 
the  trunks  and  branches  of  the  nerves,  in  which  the 
majority  measure  from  -^-^  to  of  an  inch  in 

diameter.  As  they  approach  the  brain  or  spinal  cord, 
and  generally  also  in  the  tissues  in  which  they  are  dis- 
tributed, they  gradually  become  smaller.  In  the  grey 
or  vesicular  substance  of  the  brain  or  spinal  cord,  they 
generally  do  not  measure  more  than  from  yo"o"ot 
Tihiii  of  an  inch. 

(b.)  Non-Medullated  Fibres.— The  fibres  of  the  second  kind  (Fig. 
306),  which  constitute  the  whole  of  the  branches  of  the  olfactory  and 
auditory  nerves,  the  principal  part  of  the  trunk  and  branches  of  the  sym- 
pathetic nerves,  and  are  mingled  in  various  proportions  in  the  cerebro- 
spinal nerves,  differ  from  the  preceding,  chiefly  in  their  fineness,  being 


Fig.  30.5.- 
Ranvier  in 


-A  node  of 
medul- 
1  a  t  e  d  n  erve-fibre, 
viewed  from  above. 
The  medullary  sheath 
is  interrupted,  and  the 
primiti  ve  sheath 
th  i  c  k  e  n  e  d.  Copied 
from  Axel  Key  and 
Retzius.  X  750.  (Klein 
and  Noble  Smith.) 


72 


HAND-BOOK  OF  PHYSIOLOGY. 


only  about  J  or  as  large  in  their  course  within  the  trunks  and  branches 
of  the  nerves;  in  the  absence  of  the  double  contour;  in  their  contents 
being  apparently  uniform;  and  in  their  having,  when  in  bundles,  a  yel- 
lowish grey  hue  instead  of  the  whiteness  of  the  cerebro-sjDinal  nerves. 
These  peculiarities  depend  on  their  not  possessing  the  outer  layer  of 

A 


Fig.  306. — Grey,  pale,  or  gelatinous  nerve-fibres.  A.  From  a  branch  of  the  olfactory  nerve  of  the 
sheep;  a,  a,  two  dark-bordered  or  white  fibres  from  the  fifth  pair,  associated  with  the  pale  olfactory 
fibres.   B.  From  the  sympathetic  nerve.    X  450.   (Max  Schultze.) 

medullary  nerve-substance;  their  contents  being  composed  exclusively  of 
the  axis-cylinder.  Yet,  since  many  nerve-fibres  may  be  found  which 
appear  intermediate  in  character  between  these  two  kinds,  and  since  the 
large  fibres,  as  they  approach  both  their  central  and  their  peripheral  end, 
gradually  diminish  in  size,  and  assume  many  of  the  other  characters  of 


Fig.  307.— Several  fibres  of  a  bundle  of  meduUated  nerve-fibres  acted  upon  by  silver  nitrate  to 
show  peculiar  behavior  of  nodes  of  Ranvier  toward  their  reagent.  The  silver  has  penetrated  at  the 
nodes,  and  has  stained  the  axis-cylinder  for  a  short  distance.   (Klein  and  Noble  Snnth.) 

the  fine  fibres  of  the  sympathetic  system,  it  is  not  necessary  to  suppose 
that  there  is  any  material  dilference  in  the  two  kinds  of  fibres. 

It  is  worthy  of  note,  that  in  the  foetus,  at  an  early  period  of  develop- 
ment, all  nerve-fibres  are  non-medullatod. 


THE  NERVOUS  SYSTEM. 


73 


Course. — Every  nerve-fibre  in  its  course  proceeds  uninterruptedly 
from  its  origin  in  a  nerve-centre  to  near  its  destination,  whether  this  be 
the  periphery  of  the  body,  another  nervous  centre,  or  the  same  centre 
whence  it  issued. 

Bundles  of  fibres  run  together  in  the  nerve-trunk,  but  merely  lie  in 
apposition  with  each  other;  they  do  not  unite:  even  when  they  anas- 
tomose, there  is  no  union  of  fibres,  but  only  an  interchange  of  fibres 
between  the  anastomosing  funiculi.  Although  each  nerve-fibre  is  thus 
single  and  undivided  through  nearly  its  whole  course,  yet  as  it  approaches 
the  region  in  which  it  terminates,  individual  fibres  break  up  into  several 


Fig.  308.— Small  branch  of  a  muscular  nerve  of  the  frog,  near  its  termination,  showing  divisions 
of  the  fibres,   a,  into  two;  6,  into  three;  X  350.  (KolUker.) 

subdivisions  (Fig.  308)  before  their  final  ending.  The  medullated  nerve- 
fibres,  moreover,  lose  their  medullary  sheath  before  their  final  distribution, 
and  acquire  the  characters  more  or  less  of  non-medullated  fibres. 

Plexuses. — At  certain  parts  of  their  course,  nerves  form  plexuses, 
in  which  they  anastomose  with  each  other,  as  in  the  case  of  the  brachial 
and  lumbar  plexuses.  The  objects  of  such  interchange  of  fibres  are,  («), 
to  give  to  each  nerve  passing  o.ff  from  the  plexus,  a  wider  connection  with 
the  spinal  cord  than  it  would  have  if  it  proceeded  to  its  destination  with- 
out such  communication  with  other  nerves.  Thus,  each  nerve  by  the 
wideness  of  its  connections,  is  less  dependent  on  the  integrity  of  any  single 
portion,  whether  of  nerve-centre  or  of  nerve-trunk,  from  which  it  may 
spring,  {h)  Each  part  supplied  from  a  plexus  has  wider  relations  with 
the  nerve-centres,  and  more  extensive  sympathies;  and,  by  means  of  the 
same  arrangement,  groups  of  muscles  may  be  co-ordinated,  every  member 


74 


HAND-BOOK  OF  PHYSIOLOGY. 


of  the  group  receiving  motor  filaments  from  the  same  parts  of  the  nerve- 
centre,  (c)  Any  given  part,  say  a  limb,  is  less  dependent  upon  the  integ- 
rity of  any  one  nerve,  (d)  A  plexus  is  frequently  the  means  by  which 
centripetal  and  centrifugal  fibres  are  conveniently  mingled  for  distribution, 
as  in  the  case  of  the  pneumogastric  nerve,  which  receives  motor  filaments, 
near  its  origin,  from  the  spinal  accessory. 

As  medulhited  nerve-fibres  approach  their  terminations  they  lose  their 
medullary  sheath,  and  consist  then  merely  of  axis-cylinder  and  primitive 
sheath.  They  then  lose  also  the  latter,  and  only  the  axis-cylinder  is  left, 
with  here  and  there  a  nerve-corpuscle  partly  rolled  around  it.  Finally, 
even  this  investment  ceases,  and  the  axis-cylinder  breaks  up  into  its  ele- 
mentary fibrillfe. 

Peripheral  Nerve  Termikatioks. 

(a.)  Sensory. — (1.)  Pacinian  Corjjnscles. — The  Pacinian  bodies  or 
corpuscles  (Figs.  309  and  310),  named  after  their  discoverer  Pacini,  are 
little  elongated  oval  bodies,  situated  on  some  of  the  cerebro-spinal  and 
sympathetic  nerves,  especially  the  cutaneous  nerves  of  the  hands  and  feet; 
and  on  branches  of  the  large  sympathetic  plexus  about  the  abdominal  aorta 
(Kolliker).  They  often  occur  also  on  the  nerves  of  the  mesentery,  and 
are  especially  well  seen  in  the  mesentery  of  the  cat.  They  have  been  ob- 
served also  in  the  pancreas,  lymphatic  glands  and  thyroid  glands,  as  well 
as  in  the  penis  of  the  cat.  Each  corpuscle  is  attached  by  a  narrow  pedicle 
to  the  nerve  on  which  it  is  situated,  and  is  formed  of  several  concentric 
layers  of  fine  membrane,  consisting  of  a  hyaline  ground-membrane  with 
connective-tissue  fibres,  each  layer  being  lined  by  endothelium  (Fig.  310^; 
through  its  pedicle  passes  a  single  nerve-fibre,  whioli,  after  traversing  the 
several  concentric  layers  and  their  immediate  spaces,  enters  a  central  cavity, 
and,  gradually  losing  its  dark  border,  and  becoming  smaller,  terminates 
at  or  near  the  distal  end  of  the  cavity,  in  a  knob-like  enlargement,  or  in  a 
bifurcation.  The  enlargement  commonly  found  at  the  end  of  the  fibre, 
is  said  by  Pacini  to  resemble  a  ganglion  corpuscle;  but  this  observation 
has  not  been  confirmed.  In  some  cases  two  nerves  have  been  seen  entering 
one  Pacinian  body,  and  in  others  a  nerve  after  passing  unaltered  through 
one,  has  been  observed  to  terminate  in  a  second  Pacinian  corpuscle. 
The  physiological  import  of  these  bodies  is  still  obscure.  Closely  allied  to 
Pacinian  corpuscles,  except  that  they  are  smaller  and  longer,  with  a  row 
of  nuclei  around  the  central  termination  of  the  nerve  in  the  core,  are 
corpuscles  of  Berbst,  which  have  been  found  chiefly  in  the  tongues  of 
ducks.  The  capsules  are  nearer  together,  and  toward  the  centre  the  en- 
dothelial sheath  appears  to  be  absent. 

(2.)  End-bulbs  are  found  in  the  conjunctiva,  in  the  penis  and  clitoris, 
in  the  skin,  and  in  ten(k)n:  ea(^h  is  composed  of  a  modullatod  nerve-fibre 


THE  NERVOUS  SYSTEM.  75 

which  terminates  in  corpuscles  of  various  shapes,  with  a  capsule  containing 
a  transparent  or  striated  mass,  in  the  centre  of  which  terminates  the  axis- 
cylinder  of  the  nerve- fibre,  the  ending  of  which  is  somewhat  clubbed 
(Fig.  230). 

(3.)  Touch  corpuscles  (Fig.  229)  are  found  in  the  papillae  of  the  skm 
or  among  its  epithelium;  they  may  be  simple  or  compound;  when  simple 
they  are  large  and  slightly  flattened  transparent  nucleated  ganglion  cells 


Fig.  309.  Fig.  310. 

Fig.  309.— Extremities  of  a  nerve  of  the  finger  with  Pacinian  corpuscles  attached,  about  the 
natural  size  (adapted  from  Henle  and  KoUiker). 

Fig.  310.— Pacinian  corpuscle  of  the  cafs  mesentery.  The  stalk  consists  of  a  nerve-fibre  (N)  with 
its  thick  outer  sheath.  The  peripheral  capsules  of  the  Pacinian  corpuscle  are  continuous  with  the 
outer  sheath  of  the  stalk.  The  intermediary  part  becomes  much  narrower  near  the  entrance  of  the 
axis-cyUnder  into  the  clear  central  mass.  A  hook-shaped  termination  with  the  end-bulb  (T)  is  seen 
in  the  upper  part.  A  blood-vessel  (V)  enters  the  Pacinian  corpuscle,  and  approaches  the  end-bulb:  it 
possesses  a  sheath  which  is  the  continuation  of  the  peripheral  capsules  of  the  Pacinian  corpuscle. 
X  100.   (Klein  and  Noble  Smith.) 

enclosed  in  a  capsule;  when  compound  the  capsule  contains  several  small 
cells.  The  corpuscles  of  Grandry  form  another  variety,  and  have  been 
noticed  in  the  beaks  and  tongues  of  birds.  They  consist  of  corpuscles  oval 
or  spherical,  contained  within  a  delicate  nucleated  sheath,  and  containing 
several  cells,  two  or  more  compressed  vertically.  The  cells  are  granular 
and  transparent,  with  a  nucleus.  The  nerve  enters  on  one  side,  and  laying 
aside  its  medullary  sheath,  terminates  in  or  between  the  cells. 


76 


HAND-BOOK  OF  PHYSIOLOGY. 


(4.)  In  plexuses,  as  in  the  cornea,  both  sub-epithelial  and  also  intra- 
epithelial. 

(5.)  In  cells,  as  in  the  salivary  glands  (p.  228,  Vol.  I.),  and  in  the  special 
sense  organs.  To  the  latter,  further  allusion  will  be  made  in  a  future 
chapter. 

(b.)  Motory. — (1.)  In  tmstriped  muscle,  the  nerves  first  of  all  form 
"a  plexus,  called  the  ground  plexus  (Arnold),  corresponding  to  each  group 
of  muscle  bundles;  the  plexus  is  made  by  the  anastomosis  of  tlie  primitive 
fibrils  of  the  axis-cylinders.    From  the  ground  plexus,  branches  pass  off, 


Fig.  311.— Summit  of  a  Pacinian  corpuscle  of  the  human  finger,  showing  the  endothelial  mem- 
branes lining  the  capsules,    x  220.   (Klein  and  Noble  Smith.) 

and  again  anastomosing,  form  plexuses  which  correspond  to  eacli  muscle 
bundle, — intermediary  j^lexuses.  From  these  plexuses  branches  consisting 
of  primitive  fibrils  pass  in  between  the  individual  fibres  and  anastomose. 
These  fibrils  either  send  off  finer  branches,  or  terminate  themselves  in  the 
nuclei  of  the  muscle  cells. 

(2.)  In  striped  muscle  the  nerves  end  in  the  so-called  ^'motorial  end- 
plates,''  having  first  formed,  as  in  the  case  of  unstriped  fibres,  ground 
and  intermediary  plexuses.  The  nerves  are,  however,  medullated,  and 
when  a  branch  of  the  intermediary  plexus  passes  to  enter  a  muscle-fibre, 
its  primitive  sheath  becomes  continuous  with  the  sarcolemma,  and  tlie 
axis-cylinder  forms  a  network  of  its  fibrils  on  the  surface  of  the  fibre.  This 
network  lies  embedded  in  a  flattened  granular  mass  containing  nuclei  of 
several  kinds;  this  is  the  vio/orial  e)id-plate  (Fig.  312).  In  batrachia, 
besides  end-plates,  there  is  another  way  in  which  the  nerves  end  in  the 
muscle-fibres,  viz.,  by  rounded  extremities,  to  which  oblong  nuclei  are 
attached. 


THE  NERVOUS  SYSTEM. 


77 


Nerve  Cells  or  Corpuscles. 

The  vesicular  nervous  substance  contains,  as  its  name  implies,  vesi- 
cles or  corpuscles,  in  addition  to  fibres;  and  a  structure,  thus  composed 
of  corpuscles  and  inter-communicating  fibres,  constitutes  a  nerve-centre; 
the  chief  nerve-centres  being  the  grey  matter  of  the  brain  and  spinal  cord, 
and  the  various  ganglia.    In  the  brain  and  spinal  cord  a  fine  stroma  of 


Fig.  312. — Two  striped  muscle-fibres  of  the  hyoglossus  of  frog,  a,  Nerve  end-plate;  &,  nerve 
fibres  leaving  the  end-plate;  c,  nerve-fibres,  terminating  after  dividing  into  branches;  d.  a  nucleus  in 
which  two  nerve-fibres  anastomose,    x  600.  (Arndt.) 

neuroglia  (p.  34, Vol. I.),  extends  throughout  both  the  fibrous  and  vesicular 
nervous  substance,  and  forms  a  supporting  and  investing  framework  for 
the  whole. 

The  nerve-corpuscles  which  give  to  the  ganglia  and  to  certain  parts 
of  the  brain  and  spinal  cord  the  peculiar  greyish  or  reddish-grey  aspect 
by  which  these  parts  are  characterized,  are  large,  nucleated  cells,  filled 
with  a  finely  granular  material,  some  of  which  is  often  dark  like  pigment: 


78 


HAT^D-BOOK  OF  PHYSIOLOGY. 


tlie  nucleus  containing  a  nucleolus.  Besides  varying  much  in  shape,  partly 
in  consequence  of  mutual  pressure,  they  present  such  other  varieties  as 
make  it  probable  either  that  there  are  two  dillerent  kinds,  or  that,  in  the 
stages  of  their  development,  they  pass  through  very  diiferent  forms.  Some 
of  them  are  small,  generally  spherical  or  ovoid,  and  have  a  regular  uninter- 
rupted outline.  These  simple  nerve-corpuscles  are  most  numerous  in  the 
sympathetic  ganglia;  each  is  enclosed  in  a  nucleated  sheath.  Others, 

which  are  called  caudate  or  stellate  nerve-cor- 
puscles (Fig.  313),  are  larger,  and  have  one, 
two,  or  more  long  processes  issuing  from 
them,  the  cells  being  called  respectively  ^ini- 
polar,  bipolar,  or  multipolar;  which  pro- 
cesses often  divide  and  subdivide,  and  appear 
tubular,  and  filled  with  the  same  kind  of 
granular  material  that  is  contained  within  the 
corpuscle.  Of  these  processes  some  appear 
to  taper  to  a  point  and  terminate  at  a  greater 
or  less  distance  from  the  corpuscle;  some  ap- 
pear to  anastomose  with  similar  offsets  from 
other  corpuscles;  while  others  are  continuous 
with  nerve  -fibres,  the  prolongation  from  the 
cell  by  degrees  assuming  the  characters  of  the 
nerve-fibre  with  which  it  is  continuous. 

G-anglion-cells  are  each  enclosed  in  a  trans- 
parent membranous  capsule  similar  in  appear- 
ance to  the  nucleated  sheath  of  Schwann  in 
nerve-fibres:  within  this  capsule  is  a  layer  of 
small  flattened  cells. 
That  process  of  a  nerve-cell  which  becomes  continuous  with  a  nerve- 
fibre  is  always  unbranched,  as  it  leaves  the  cell.  It  at  first  has  all  the 
characters  of  an  axis-cylinder,  but  soon  acquires  a  medullary  sheath,  and 
then  may  be  termed  a  nerve-fibre.  This  continuity  of  nerve-cells  and 
fibres  may  be  readily  traced  out  in  the  anterior  cornua  of  the  grey  matter 
of  the  spinal  cord.  In  many  large  branched  nerve-cells  a  distinctly  fibril- 
lated  appearance  is  observable;  the  fibrill^  are  probably  continuous  with 
those  of  the  axis-cylinder  of  a  nerve. 


Fig.  313.— GangKon  nerve-corpiis- 
cles  of  different  shapes.  (Klein  and 
Noble  Smith.) 


The  Functions  of  Nerve  Fibres. 

It  will  be  evident  from  the  account  of  nervous  action  previously  given 
(p.  45  rf  scq.,  Vol.  II.)  that  nerve-fibres  are  stimulated  to  act  by  anytliing 
which  increases  their  irritability,  but  that  they  are  incapable  of  originating 
of  themselves  the  condition  necessary  for  the  manifestation  of  their  own 
functions.    When  a  cerebro-spinal  nerve-fibre  is  irritated  in  the  living 


THE  NERVOUS  SYSTEM. 


79 


body,  as  by  pinching,  or  by  heat,  or  by  electrifying  it,  there  is,  under 
ordinary  circumstances,  one  of  two  effects, — either  there  is  pain,  or  there 
is  twitching  of  one  or  more  muscles  to  which  the  nerve  distributes  its 
fibres.  From  various  considerations  it  is  certain  that  pain  is  always  the 
result  of  a  change  in  the  nerve-cells  of  the  brain.  Therefore,  in  such 
an  experiment  as  that  referred  to,  the  irritation  of  the  nerve-fibre  seems 
to  the  experimenter  to  be  conducted  in  one  of  two  directions,  i.e.,  either 
to  the  brain  {central  termination  o  f  the  fibre),  when  there  is  pain,  or  to 
a  muscle  (peripheral  termination)  when  there  is  movement. 


Fig.  314.— An  isolated  sympathetic  ganglion  cell  of  man,  showing  sheath  with  nucleated-ceU  lin- 
ing, B.  A.  GangUon-cell,  with  nucleus  and  neucleolus.  C.  Branched  process.  D.  Unbranched  pro- 
cess.  Copied  from  Key  and  Retzius.    X  750.   (Klein  and  Noble  Smith.) 

The  effect  of  this  simple  experiment  is  a  type  of  what  always  occurs 
when  nerve-fibres  are  engaged  in  the  performance  of  their  functions. 
The  result  of  stimulating  them,  which  roughly  imitates  what  happens 
naturally  in  the  body,  is  found  to  occur  at  one  or  other  of  their  ex- 
tremities, central  or  peripheral,  never  at  both;  and  in  accordance  with 
this  fact,  and  because,  for  any  given  nerve-fibre,  the  result  is  always  the 
same,  nerves  are  commonly  classed  as  sensory  or  motor. 

It  may  be  well  to  state,  in  order  to  avoid  confusion,  that  the  apparent 
conduction  in  both  directions,  which  seems  to  occur  when  a  nerve,  say 
the  ulnar  or  median,  is  irritated,  depends  on  the  fact  that  both  motor  and 
sensory  fibres  are  bound  up  together  in  the  same  nerve-trunlcs — an  arrange- 


80 


HAND-BOOK  OF  PHYSIOLOGY. 


ment  which,  for  medium-sized  and  large  nerves,  is  the  rule  rather  than 
the  exception. 

Conduction  in  Nerves. — A  nerve  when  removed  from  the  body  will 
be  found  to  conduct  electrical  impressions  in  either  direction  equally  well, 
and  microscopic  examination  fails  to  discover  the  slightest  essential  differ- 
ence between  motor  and  sensory  nerve-fibres.  The  question,  therefore, 
naturally  arises,  whether  the  conduction  of  a  stimulus  in  the  living  body, 
in  one  direction  only,  is  not  rather  apparent  than  real,  the  difference  in 
the  result  being  due  to  the  different  connections  of  the  two  kinds  of 
nerve-fibres  respectively  at  their  extremities.  In  other  words,  when  the 
stimulation  of  a  nerve-fibre  causes  pain,  the  result  is  due  to  its  central 
extremity  being  in  connection  with  structures  which  alone  can  give  rise 
to  the  sensation,  while  its  perijjlieral  extremity,  although  the  stimulus  is 
equally  conducted  to  it,  has  no  connection  with  a  structure  which  can 
respond  to  the  irritation  in  any  manner  sensible  to  the  observer.  So, 
when  motion  is  the  result  of  a  like  irritation,  it  is  because  the  jjenpheral 
extremity  of  the  nerve-fibre  is  in  connection  with  muscles  which  will  re- 
spond by  contracting,  while  its  central  extremity,  although  equally 
stimulated,  has  no  means  of  showing  the  fact  by  any  evident  result. 

That  this  is  the  true  explanation  is  made  highly  probable,  not  merely 
by  the  absense  of  any  structural  differences  in  the  two  kinds  of  nerve-fibre, 
but  also  by  the  fact,  proved  by  direct  experiment,  that  if  a  centripetal 
nerve  (gustatory)  be  divided,  and  its  central  portion  be  made  to  unite  with 
the  distal  portion  of  a  divided  motor  nerve  (hypoglossal)  the  effect  of  irri- 
tating the  former  after  the  parts  have  healed,  is  to  excite  contraction  in 
the  muscles  supplied  by  the  latter.    (Philippeaux  and  Vulpian. ) 

Classification  of  Nerve-Fibres. — 1.  Centripetal,  afferent,  or,  2. 
Centrifugal,  afferent,  or  motor.    3.  Intercentral. 

Centrij^etal  or  afferent,  and  centrifugal  or  eff^erent,  are  frequently  em- 
ployed in  connection  with  nerve-fibres  in  lieu  of  the  corresponding  terms 
sensory  and  motor,  because  the  result  of  stimulating  a  nerve  of  the  former 
kind  is  not  always  the  production  of  pain  or  other  form  of  sensation,  nor 
is  motion  the  invariable  result  of  stimulating  the  latter. 

Conduction  m  centrij^etal  nerves  may  cause  (a)  pain,  or  some  other  kind 
of  sensation;  or  (l)  reflex  action;  or  (c)  inhibition,  or  restraint  of  action. 

Conduction  in  centrifugal  nerves,  may  cause  (a)  contraction  of  muscle 
(p.  25,  Vol.  II.),  (motor  nerves);  ifi)  it  may  influence  nutrition  (trophic 
nerves);  or  (c)  may  influence  secretion  (secretory  nerves). 

The  term  intercentral  is  applied  to  those  nerve-fibres  which  connect 
more  or  less  distinct  nerve-centres,  and  may,  therefore,  be  said  to  have  no 
peripheral  distribution,  in  the  ordinary  sense  of  the  term. 

It  is  a  law  of  action  in  all  nerve-fibres,  and  corresponds  with  the  con- 
tinuity and  simplicity  of  their  course,  that  an  impression  made  on  any 


THE  NERVOUS  SYSTEM. 


81 


fibre,  is  simply  and  uninterruptedly  transmitted  along  it,  without  being 
imparted  or  diffused  to  any  of  the  fibres  lying  near  it.  In  other  words, 
all  nerve-fibres  are  mere  conductors  of  impressions.  Their  adaptation  to 
this  purpose  is,  perhaps,  due  to  the  contents  of  each  fibre  being  completely 
isolated  from  those  of  adjacent  fibres  by  the  membrane  or  sheath  in  which 
each  is  enclosed,  and  which  acts,  it  may  be  supposed,  just  as  silk  or  other 
non-conductors  of  electricity  do,  which,  when  covering  a  wire,  prevent  the 
electric  condition  of  the  wire  from  being  conducted  into  the  surrounding 
medium. 

Velocity  of  Nerve-force. — The  change  which  a  stimulus  sets  upon  a 
nerve,  of  the  exact  nature  of  which  we  are  unacquainted,  appears  to  travel 
along  a  nerve-fibre  in  both  directions  in  the  form  of  a  wave.  Nervous 
force  travels  along  nerve-fibres  with  considerable  velocity.  Helmholtz  and 
Baxt  have  estimated  the  average  rate  of  conduction  in  human  motor 
nerves  at  111  feet  (nearly  29  metres)  per  second;  this  result  agreeing  very 
closely  with  that  previously  obtained  by  Hirsch.  Eutherford^'s  observations 
agree  with  those  of  Von  Wittich,  that  the  rate  of  transmission  in  sensory 
nerves  is  about  140  feet  per  second. 

Conduction  in  Sensory  Nerves. — Centripetal  nerves  appear  (p. 
80,  Vol.  II. )  able  to  convey  impressions  only  from  the  parts  in  which  they 
are  distributed,  toward  the  nerve-centre  from  which  they  arise,  or  to 
which  they  tend.  Thus,  when  a  sensitive  nerve  is  divided,  and  irritation  is 
applied  to  the  end  of  the  proximal  portion,  i.e.,  of  the  portion  still  con- 
nected with  the  nervous  centre,  sensation  is  perceived,  or  a  reflex  action 
ensues;  but,  when  the  end  of  the  distal  portion  of  the  divided  nerve  is 
irritated,  no  effect  appears.  When  an  impression  is  made  upon  any  part 
of  the  course  of  a  sensory  nerve,  the  mind  may  perceive  it  as  if  it  were 
made  not  only  upon  the  point  to  which  the  stimulus  is  applied,  but  also 
upon  all  the  points  in  which  the  fibres  of  the  irritated  nerve  are  distrib- 
uted: in  other  words,  the  effect  is  the  same  as  if  the  irritation  were  applied 
to  the  parts  supplied  by  the  branches  of  the  nerve.  When  the  whole 
trunk  of  the  nerve  is  irritated,  the  sensation  is  felt  at  all  the  parts  which 
receive  branches  from  it;  but  when  only  individual  portions  of  the  trunk 
are  irritated,  the  sensation  is  perceived  at  those  parts  only  which  are  sup- 
plied by  the  several  portions.  Thus,  if  we  compress  the  ulnar  nerve 
where  it  lies  at  the  inner  side  of  the  elbow-joint,  behind  the  internal 
condyle,  we  have  the  sensation  of  *^pins  and  needles, or  of  a  shock,  in  the 
parts  to  which  its  fibres  are  distributed,  namely,  in  the  palm  and  back  of 
the  hand,  and  in  the  fifth  and  ulna  half  of  the  fourth  finger.  When 
stronger  pressure  is  made,  the  sensations  are  felt  in  the  fore-arm  also;  and 
if  the  mode  and  direction  of  the  pressure  be  varied,  the  sensation  is  felt 
by  turns  in  the  fourth  finger,  in  the  fifth,  and  in  the  palm  of  the  hand,  or 
m  the  back  of  the  hand,  according  as  different  fibres  or  fasciculi  of  fibres 
are  more  pressed  upon  than  others. 
Vol.  II.— 6. 


82 


HAND-BOOK  OF  PHYSIOLOaY. 


Illustrations. -^li  is  in  accordance  with  this  law,  that  when  parts  are 
deprived  of  sensibility  by  compression  or  division  of  the  nerves  supplying 
them,  irritation  of  the  portion  of  the  nerve  connected  with  the  brain  still 
excites  sensations  which  are  felt  as  if  derived  from  the  parts  to  which  the 
peripheral  extremities  of  the  nerve-fibres  are  distributed.  Thus,  there  are 
cases  of  paralysis  in  which  the  limbs  are  totally  insensible  to  external 
stimuli,  yet  are  the  seat  of  most  violent  pain,  resulting  apparently  from 
irritation  of  the  sound  part  of  the  trunk  of  the  nerve  still  in  connection 
with  the  brain,  or  from  irritation  of  those  parts  of  the  nervous  centre  from 
which  the  sensory  nerve  or  nerves  which  supply  the  paralyzed  limbs 
originate.  An  illustration  of  the  same  law  is  also  afforded  by  the  cases  in 
which  division  of  a  nerve  for  the  cure  of  neuralgic  pain  is  found  useless, 
and  in  which  the  pain  continues  or  returns,  though  portions  of  the  nerves 
be  removed.  In  such  cases,  the  disease  is  probably  seated  nearer  the 
nervous  centre  than  the  part  at  which  the  division  of  the  nerve  is  made, 
or  it  may  be  in  the  nervous  centre  itself.  In  the  same  way  may  be  ex- 
plained the  fact,  that  when  part  of  a  limb  has  been  removed  by  amputation, 
the  remaining  portions  of  the  nerves  may  give  rise  to  sensations  which  the 
mind  refers  to  the  lost  part.  When  the  stump  is  healed,  the  sensations 
which  we  are  accustomed  to  have  in  a  sound  limb  are  still  felt;  and 
tingling  and  pains  are  referred  to  the  parts  that  are  lost,  or  to  particular 
portions  of  them,  as  to  single  toes,  to  the  sole  of  the  foot,  to  the  dorsum 
of  the  foot,  etc. 

It  must  not  be  assumed,  as  it  often  has  been,  that  the  mind  has  no 
power  of  discriminating  the  very  point  in  the  length  of  any  nerve-fibre  to 
which  an  irritation  is  applied.  Even  in  the  instances  referred  to,  the  mind 
perceives  the  pressure  of  a  nerve  at  the  point  of  pressure,  as  well  as  in  the 
seeming  sensations  derived  from  the  extremities  of  the  fibres:  and  in 
stumps,  pain  is  felt  in  the  stump,  as  well  as,  seemingly,  in  the  parts  re- 
moved. It  is  not  quite  certain  whether  those  sensations  are  due  to  con- 
duction through  the  nerve  fibres  which  are  on  their  way  to  be  distributed 
elsewhere,  or  through  the  sentient  extremities  of  nerves  which  are  them- 
selves distributed  to  the  many  trunks  of  the  nerves,  the  nervi  oiervorim. 
The  latter  is  the  more  probable  supposition. 

When,  in  a  part  of  the  body  which  receives  two  sensory  nerves,  one  is 
paralyzed,  the  other  may  or  may  not  be  inadequate  to  maintain  the  sensi- 
bility of  the  entire  part;  the  extent  to  which  the  sensibility  is  preserved 
corresponding  probably  with  the  number  of  the  fibres  unatt'ected  by  the 
paralysis.  There  are  instances  in  which  the  trunk  of  the  chief  sensory 
nerve  supplied  to  a  part  having  been  divided,  the  sensibility  of  the  part 
is  still  preserved  by  intercommunicating  fibres  from  a  neighboring  nerve- 
trunk. 

Conduction  in  the  Nerves  of  Special  Sense. — The  laws  of  con- 
duction in  the  olfactory,  optic,  auditory,  gustatory — resemble  in  many 
aspects  those  of  conduction  in  tlie  nerves  of  common  sensation,  just  de- 
scribed. Tlius  the  effect  is  always  cvufral;  stimulation  of  the  trunk  of 
the  lu^rve  j)r()duces  the  same  elfect  as  tluit  ol'  its  extremities,  and  if  the 


THE  NERVOUS  SYSTEM.  .83 

nerve  De  severed,  it  is  the  central  and  not  the  peripheral  extremity  which 
responds  to  irritation,  although  the  sensation  is  referred  to  the  periphery. 
There  are,  however,  certain  peculiarities  in  the  effect.  Thus  the  various 
stimuli,  which  might  cause,  through  an  ordinary  sensitive  nerve,  the  sense 
of  pain,  would,  if  applied  to  the  optic  nerve,  cause  a  sensation  as  of  flashes 
of  light;  if  applied  to  the  olfactory,  there  would  be  a  sense  as  of  something 
smelt.    And  so  with  the  other  two. 

Hence  the  explanation  of  so-called  suhjective  sensations.  Irritation  in 
the  optic  nerve,  or  the  part  of  the  brain  from  which  it  arises,  may  cause  a 
patient  to  believe  he  sees  flashes  of  light,  and  among  the  commonest 
troubles  of  the  nerves  of  special  sense,  is  the  distressing  noise  in  the  head 
(tinnitus  aurium),  which  depends  on  some  unknown  stimulation  of  the 
auditory  nerve  or  centre  quite  unconnected  with  external  sounds. 

Conduction  in  Motor  Nerves. — Conduction  in  motor  nerves  pre- 
sents a  remarkable  contrast  with  the  foregoing.  Thus — the  effect  of 
applying  a  stimulus  to  the  motor  nerve  is  always  noticeable,  at  the  periph- 
eral extremity,  in  the  contraction  of  muscles  supplied  by  it.  If  a  motor 
nerve  be  severed,  irritation  of  the  distal  portion  causes  contraction  of 
muscle,  but  no  effect  whatever  is  produced  by  stimulating  that  part  of 
the  nerve  which  is  still  in  direct  connection  with  the  nerve-centre. 

Contractions  are  excited  in  all  the  muscles  supplied  by  the  branches 
given  off  by  the  nerve  below  the  point  irritated,  and  in  those  muscles  alone: 
the  muscles  supplied  by  the  branches  which  come  off  from  the  nerve  at  a 
higher  point  than  that  irritated,  are  not  directly  excited  to  contraction. 
And  it  is  from  the  same  fact  that,  when  a  motor  nerve  enters  a  plexus  and 
contributes  with  other  nerves  to  the  formation  of  a  nervous  trunk  pro- 
ceeding from  the  plexus,  it  does  not  impart  motor  power  to  the  whole  of 
that  trunk,  but  only  retains  it  isolated  in  the  fibres  which  form  its  con- 
tinuation in  the  branches  of  that  trunk. 

FuKCTiONS  or  Nerye-Centees. 

The  functions  of  nerve-centres  may  be  classified  as  follows: — 1. 
Conduction.  2.  Transference.  3.  Reflection.  4.  Automatism.  5.  Aug- 
mentation.   6.  Inhibition. 

1.  Conduction. — Conduction  in  or  through  nerve-centres  may  be 
thus  simply  illustrated.  The  food  in  a  given  portion  of  the  intestines, 
acting  as  a  stimulus,  produces  a  certain  impression  on  the  nerves  in  the 
mucous  membrane,  which  impression  is  conveyed  through  them  to  the 
adjacent  ganglia  of  the  sympathetic.  In  ordinary  cases,  the  consequence 
of  such  an  impression  on  the  ganglia  is  the  movement  by  reflex  action 
(p.  85,  Vol.  II.)  of  the  muscular  coat  of  that  and  the  adjacent  part  of 
the  canal.  But  if  irritant  substances  be  mingled  with  the  food,  the 
sharper  stimulus  produces  a  stronger  impression,  and  this  is  conducted 


84 


HAND-BOOK  OF  PHYSIOLOGY. 


through  the  nearest  ganglia  to  others  more  and  more  distant;  and,  from 
all  these,,  reflex  motor  impulses  issuing,  excite  a  wide-extended  and  more 
forcible  action  of  the  intestines.  Or  even  through  the  sympathetic 
ganglia,  the  impression  may  be  further  conducted  to  the  ganglia  of  the 
spinal  nerves,  and  through  them  to  the  spinal  cord,  whence  may  issue 
motor  impulses  to  the  abdominal  and  other  muscles,  producing  cramp. 
And  yet  further,  the  same  morbid  impression  may  be  conducted  through 
the  spinal  cord  to  the  brain,  where  it  may  be  felt.  In  the  opposite  direc- 
tion, mental  influence  may  be  conducted  from  the  brain  through  a  suc- 
cession of  nervous  centres — the  spinal  cord  and  ganglia,  and  one  or  more 
ganglia  of  the  sympathetic — to  produce  the  influence  of  the  mind  on  the 
digestive  and  other  organs;  altering  both  the  quantity  and  quality  of 
their  secretions. 

2.  Transference. — It  has  been  previously  stated  that  impressions 
conveyed  by  any  centripetal  nerve-fibre  travel  uninterruptedly  through- 
out its  whole  length,  and  are  not  communicated  to  adjacent  fibres. 

When  such  aii  impression,  however,  reaches  a  nerve-centre,  it  may 
seem  to  be  communicated  to  another  fibre  or  fibres;  as  pain  or  some  other 
kind  of  sensation  may  be  felt  in  a  part  different  altogether  from  that  from 
which,  so  to  speak,  the  stimulus  started.  Thus,  in  disease  of  the  hip, 
there  may  be  pain  in  the  knee.  This  apparent  change  of  place  of  a  sen- 
sation to  a  part  to  which  it  would  not  seem  properly  to  belong  is  termed 
transference. 

The  transference  of  impressions  may  be  illustrated  by  the  fact  just 
referred  to, — the  pain  in  the  knee,  which  is  a  common  sign  of  disease  of 
the  hip.  In  this  case  the  impression  made  by  the  disease  on  the  nerves 
of  the  hip- joint  is  conveyed  to  the  spinal  cord;  there  it  is  transferred  to 
the  central  ends  or  connections  of  the  nerve-fibres  which  are  distributed 
about  the  knee.  Through  these  the  transferred  impression  is  conducted 
to  the  brain,  which,  referring  the  sensation  to  the  part  from  which  it 
usually  through  these  fibres  receives  impressions,  feels  as  if  the  disease 
and  the  source  of  pain  were  in  the  knee.  At  the  same  time  that  it  is 
transferred,  primary  impression  may  be  also  conducted  to  the  brain; 
and  in  this  case  the  pain  is  felt  in  both  the  hip  and  the  knee.  And  so,  in 
whatever  part  of  the  respiratory  organs  an  irritation  may  be  seated,  the 
impression  it  produces,  being  conducted  to  the  medulla  oblongata,  is 
transferred  to  the  central  connections  of  the  nerves  of  the  larynx;  and 
thence,  being  conducted  as  in  the  last  case  to  the  brain,  the  latter  per- 
ceives the  peculiar  sensation  of  tickling  in  the  glottis,  which  excites  the 
act  of  coughing.  Or,  again,  when  the  sun's  light  falls  strongly  on  the 
eye,  a  tickling  may  be  felt  in  the  nose,  exciting  sneezing. 

A  variety  of  transference,  which  may  be  termed  radiation  of  impres- 
sions, is  shown  when  an  impression  received  by  a  nervous  centre  is  dif- 
fused to  many  other  })arts  in  the  same  centre,  and  produces  sensations  ex- 


THE  NERVOUS  SYSTEM. 


85 


tending  far  beyond  the  part  from  which  the  primary  impression  was 
derived.  Hence,  as  in  the  former  cases,  result  various  kinds  of  what  have 
been  denominated  sympathetic  sensations.  Sometimes  such  sensations 
are  referred  to  almost  every  part  of  the  body:  as  in  the  shock  and  ting- 
ling of  the  skin  produced  by  some  startling  noise.  Sometimes  only  the 
parts  immediately  surrounding  the  point  first  irritated  participate  in  the 
effects  of  the  irritation;  thus  the  aching  of  a  tooth  may  be  accompanied 
by  pain  in  the  adjoining  teeth,  and  in  all  the  surrounding  parts  of  the 
face;  th'e  explanation  of  such  a  case  being,  that  the  irritation  conveyed 
to  the  brain  by  the  nerve-fibres  of  the  diseased  tooth  is  radiated  to  the 
central  ends  of  adjoining  fibres,  and  that  the  mind  perceives  this  second- 
ary impression  as  if  it  were  derived  from  the  peripheral  ends  of  the  fibres. 

3.  Reflection. — In  the  cases  of  transference  of  nerve-force  just 
described,  it  has  been  said  that  all  that  need  be  assumed  is  a  communica- 
tion of  the  excited  condition  of  an  afferent  nerve  to  other  parts  of  its 
nerve-centre  than  that  from  which  it  takes  its  origin.  In  the  case  of 
reflection,  on  the  other  hand,  the  stimulus  having  been  conveyed  to  a 
nerve-centre  by  a  centripetal  nerve,  is  conducted  away  again  by  a  cen- 
trifugal nerve,  and  effects  some  change — motor,  secretory  or  nutritive,  at 
the  peripheral  extremity  of  the  latter — the  difference  in  effect  depending 
on  the  variety  of  centrifugal  nerve  secondarily  affected.  As  in  transfer- 
ence, the  reflection  may  take  place  from  a  certain  limited  set  of  cen- 
tripetal nerves  to  a  corresponding  and  related  set  of  centrifugal  nerves; 
as  when  in  consequence  of  the  impression  of  light  on  the  retina,  the  iris 
contracts,  but  no  other  muscle  moves.  Or  the  reflection  may  extend  to 
widely  different  parts:  as  when  an  irritation  in  the  larynx  brings  all  the 
muscles  engaged  in  expiration  into  coincident  movement.  Eeflex  move- 
ments, occurring  quite  independently  of  sensation,  are  generally  called 
excito-motor;  those  which  are  guided  or  accompanied  by  sensation,  but 
not  to  the  extent  of  a  distinct  perception  or  intellectual  process  are  termed 
sensori-motor. 

Laws  of  Reflex  Action. — {a)  For  the  manifestation  of  every  reflex 
action,  these  things  are  necessary:  (1),  one  or  more  perfect  centripetal 
nerve-fibres,  to  convey  an  impression;  (2),  a  nervous  centre  for  its  recep- 
tion, and  by  which  it  may  be  reflected;  (3),  one  or  more  centrifugal 
nerve-fibres,  along  which  the  impression  may  be  conducted  to  (4),  the 
muscular  or  other  tissue  by  which  the  effect  is  manifested  (p.  80,  Vol. 
II.).  In  the  absence  of  any  one  of  these  conditions,  a  proper  reflex  action 
could  not  take  place;  and  whenever,  for  example,  impressions  made  by 
external  stimuli  on  sensory  nerves  give  rise  to  motions,  these  are  never 
the  result  of  the  direct  reaction  of  the  sensory  and  motor  fibres  of  the 
nerves  on  each  other;  in  all  such  cases  the  impression  is  conveyed  by  the 
•afferent  fibres  to  a  nerve-centre,  and  is  therein  communicated  to  the 
motor  fibres. 


86 


HAND-BOOK  OF  PHYSIOLOGY. 


{!))  All  reflex  actions  are  essentially  involuntary,  though  most  of  them 
admit  of  being  modified,  controlled,  or  prevented  by  a  voluntary  effort. 

(c)  Keflex  actions  performed  in  health  have,  for  the  most  part,  a  dis- 
tinct purpose,  and  are  adapted  to  secure  some  end  desirable  for  the  well- 
being  of  the  body  ;  but,  in  disease,  many  of  them  are  irregular  and  pur- 
poseless. As  an  illustration  of  the  first  point,  may  be  mentioned  move- 
ments of  the  digestive  canal,  the  respiratory  movements,  and  the  con- 
traction of  the  eyelids  and  the  pupil  to  exclude  many  rays  of  light, 
when  the  retina  is  exposed  to  a  bright  glare.  These  and  all  other  normal 
reflex  acts  afford  also  examples  of  the  mode  in  which  the  nervous  centres 
C07nl)ine  and  arrange  co-ordinately  the  actions  of  the  nerve-fibres,  so  that 
many  muscles  may  act  together  for  the  common  end.  Another  instance 
of  the  same  kind  is  furnished  by  the  spasmodic  contractions  of  the  glottis 
on  the  contact  of  carbonic  acid,  or  any  foreign  substance,  w^ith  the  sur- 
face of  the  epiglottis  or  larynx.  Examples  of  the  purposeless  irregular 
nature  of  morbid  reflex  action  are  seen  in  the  convulsive  movements  of 
epilepsy,  and  in  the  spasms  of  tetanus  and  hydrophobia. 

{d)  Reflex  muscular  acts  are  often  more  sustained  than  those  produced 
by  the  direct  stimulus  of  muscular  nerves.  The  irritation  of  a  muscular 
organ,  or  its  motor  nerve,  produces  contraction  lasting  only  so  long  as 
the  irritation  continues;  but  irritation  applied  to  a  nervous  centre  through 
one  of  its  centripetal  nerves,  may  excite  reflex  and  harmonious  contrac- 
tions, which  last  some  time  after  the  withdrawal  of  the  stimulus  (Volk- 
mann). 

Classification  of  Reflex  Actions. — Reflex  actions  maybe  classified 
as  follows  (Kuss): — 1.  Those  in  which  both  the  centripetal  and  cen- 
trifugal nerves  concerned  are  cerehro-spinal;  e.g.,  deglutition,  sneezing, 
coughing,  and,  in  pathological  conditions,  tetanus,  epilepsy.  2.  Those 
in  which  the  centripetal  nerve  is  cerebro-spinal,  and  the  centrifugal  is 
symimtlidic,  most  often  vaso-motor;  e.g.,  secretion  of  saliva,  or  gastric 
juice;  blushing  or  pallor  of  the  skin.  3.  Those  in  which  the  centripetal 
nerve  is  of  the  sympathetic  system,  and  the  centrifugal  is  cerehro-spinal. 
The  majority  of  these  are  pathological,  as  in  the  case  of  convulsions  pro- 
duced by  intestinal  worms,  or  hysterical  convulsions.  4.  Those  in  which 
both  centripetal  and  centrifugal  nerves  are  of  the  sympathetic  system:  as, 
for  example,  the  obscure  actions  which  preside  over  the  secretion  of  the 
intestinal  fluids,  those  which  unite  the  various  generative  functions  and 
many  pathological  phenomena. 

Relations  between  the  Stimulus  aud  the  Resulting  Reflex 
Action. — Certain  rules  showing  the  relation  between  the  resulting  reflex 
action  and  the  stimulus  have  been  drawn  up  by  Pfliiger,  as  follows: — 

1.  Law  of  nnilateral  reflection. — A  slight  irritation  of  sensory  nerves 
is  reflected  along  the  motor  nerves  of  the  same  region.  Thus,  if  the  skin 
of  a  frog's  foot  be  tickled  on  the  right  side,  the  right  leg  is  drawn  up. 


THE  NERVOUS  SYSTEM. 


87 


2.  Law  of  symmetrical  reflection. — A  stronger  irritation  is  reflected, 
not  only  on  one  side,  but  also  along  the  corresponding  motor  nerves  of 
the  opposite  side.  Thus,  if  the  spinal  cord  of  a  man  has  been  severed  by 
a  stab  in  the  back,  when  one  foot  is  tickled  both  legs  will  be  drawn  up. 

3.  Law  of  intensity. — In  the  above  case,  the  contractions  will  be  more  • 
violent  on  the  side  irritated. 

4.  Law  of  radiatio7i. — If  the  irritation  (afferent  impulse)  increases,  it 
is  reflected  along  the  motor  nerves  which  spring  from  points  higher  np 
the  spinal  cord,  till  at  length  all  the  muscles  of  the  body  are  thrown  into 
action. 

Simple  and  Co-ordinated  Reflex  Actions.— In  the  simplest  form 
of  reflex  action  a  single  nerve  cell  with  an  afferent  and  an  efferent  fibre  is 
concerned,  but  in  the  majority  of  actual  actions  a  number  of  cells  are 
probably  concerned,  and  the  impression  is  as  it  were  distributed  among 
them,  and  they  act  in  concert  or  co-ordination.  This  co-ordinating 
power  belongs  to  nerve  centres. 

Primary  and  Secondary  or  Acquired  Reflex  Actions.~We 
must  carefully  distinguish  between  such  reflex  actions  which  may  be 
termed  primary,  and  those  which  are  secondary  or  acquired.  As  examples 
of  the  former  class  we  may  cite  sucking,  contraction  of  the  pupil,  drawing 
up  the  legs  when  the  toes  are  tickled,  and  many  others  which  are  performed 
as  perfectly  by  the  infant  as  by  the  adult. 

The  large  class  of  secondary  reflex  actions  consists  of  acts  which  re- 
quire for  their  first  performance  and  many  subsequent  repetitions,  an 
effort  of  will,  but  which  by  constant  repetition  are  habitually  though  not 
necessarily  performed,  mechanically,  i.e.,  without  the  intervention  of  con- 
sciousness and  volition.  As  instances  we  may  take  reading,  writing, 
walking,  etc. 

In  endeavoring  to  conceive  how  such  complicated  actions  can  be  per- 
formed without  consciousness  and  will,  we  must  suppose  that  in  the  first 
instance  the  will  directs  the  nerve-force  along  certain  channels  causing 
the  performance  of  certain  acts,  e.g.,  the  various  movements  of  flexion 
and  extension  involved  in  walking.  After  a  time,  by  constant  repetition, 
these  routes  become,  to  use  a  metaphor,  well  worn :  there  is,  as  it  were, 
a  beaten  track  along  which  the  nerve-force  travels  with  much  greater  ease 
than  formerly:  so  much  so  that  a  slight  stimulus,  such  as  the  pressure  of 
the  foot  on  the  ground,  is  sufficient  to  start  and  keep  going  indefinitely 
the  complex  reflex  actions  of  walking  during  entire  mental  abstraction, 
or  even  during  sleep.  In  such  acts  as  reading,  writing,  and  the  like, 
it  would  appear  as  if  the  will  set  the  necessary  reflex  machinery  going, 
and  that  the  reflex  actions  go  on  uninterruptedly  until  again  interfered 
with  by  the  will. 

Without  this  capacity  possessed  by  the  nervous  system  of  ^'organizing 
conscious  actions  into  more  or  less  unconscious  ones,"  education  or  training 


88 


HAND-BOOK  OF  PHYSIOLOGY. 


would  be  impossible.  A  most  important  part  of  the  process  by  which 
these  acquired  reflex  actions  come  to  be  performed  automatically  consists 
in  what  is  termed  associati07i.  If  two  acts  be  at  first  performed  voluntarily 
in  succession,  and  this  succession  is  often  repeated,  the  performance  of 
the  first  is  at  once  followed  mechanically  by  the  second.  Instances  of 
this  "force  of  habit'^  must  be  within  the  daily  experience  of  every  one. 

Of  course  it  is  only  such  actions  as  have  become  entirely  reflex  that 
can  be  performed  during  complete  unconsciousness,  as  in  sleep.  Cases 
of  somnambulism  are  of  course  familiar  to  every  one,  £lnd  authentic 
instances  are  on  record  of  persons  writing  and  even  playing  the  piano 
during  sleep. 

4.  Automatism. — To  nerve  centres,  it  is  said,  belongs  the  property 
of  originating  nerve-impulses,  as  well  as  of  receiving  them  and  conducting 
and  reflecting  them. 

The  term  automatism  is  employed  to  indicate  the  origination  of  nervous 
impulses  in  nerve-centres,  and  their  conduction  therefrom,  independently 
of  previous  reception  of  a  stimulus  from  another  part.  It  is  impossible, 
in  the  present  state  of  our  knowledge,  to  say  definitely  what  actions  in 
the  body  are  really  in  this  sense  automatic.  An  example  of  automatic 
nerve-action  has  been  already  referred  to,  i.e.,  that  of  the  respiratory 
centre,  but  the  apparently  best  examples  of  automatism  are  found, 
however,  in  the  case  of  the  cerebrum,  which  will  be  presently  considered. 

5.  and  6.  Augmentation  and  Inhibition. — Nerve  cells  not  only 
receive  and  reflect  nerve  impulses,  and  also  in  some  cases  even  originate 
such  impulses,  but  they  are  also  capable  of  increasing  the  impulse,  and 
the  result  is  what  is  called  augmentation;  and  when  a  nerve  centre  is  in 
action  its  action  is  also  capable  of  being  increased  or  diminished  (inJiibi- 
tioji)  by  afferent  impulses.  This  is  the  case  in  whatever  way  the  centre 
has  caused  the  action,  whether  of  itself  or  by  means  of  previous  afferent 
impulses.  The  action,  by  which  a  centre  is  capable  of  being  inhibited  or 
exalted,  has  been  well  shown  in  the  case  of  the  vaso-motor  centre,  before 
described  (p.  155,  Vol.  I.).  This  power,  which  can  be  exerted  from  the 
periphery,  is  very  important  in  regulating  the  action  even  of  partially 
automatic  centres  such  as  the  respiratory  centre. 

Cerebro-spinal  Nervous  System. 

The  physiology  of  the  cerebro- spinal  nervous  system  includes  that  of 
the  Spinal  Cord,  Medulla  Oblongata,  and  Brain,  of  the  several  Nerves 
given  off  from  each,  and  of  the  Ganglia  on  those  nerves. 

Membranes  of  the  Brain  and  Spinal  Cord.— The  Brain  and 
Spinal  Coi'd  are  enveloped  in  three  membranes — (1)  the  Dura  Mater, 
(2)  ilie  Arachnoid,  (3)  the  Pia  Mater. 

( 1 . )  The  Dura  Mater,  or  external  covering,  is  a  tough  membrane  com- 


1 


THE  NERVOUS  SYSTEM. 


89 


posed  of  bundles  of  connective  tissue  which  cross  at  various  angles,  and 
in  whose  interstices  branched  connective-tissue  corpuscles  lie:  it  is  lined 
by  a  thin  elastic  membrane,  and  on  the  inner  surface,  and,  where  it  is  not 


Fia.  315.— View  of  the  cerebro-  spinal  axis  of  the  nervous  system.  The  right  half  of  the  cranium 
andtrimkof  the  body  has  been  removed  by  a  vertical  section;  the  membranes  of  the  brain  and 
spinal  marrow  have  also  been  removed,  and  the  roots  and  first  part  of  the  fifth  and  ninth  cranial,  and 
ot  all  the  spinal  nerves  of  the  right  side,  have  been  dissected  out  and  laid  separately  on  the  wall  of 
the  skull  and  on  the  several  vertebrae  opposite  to  the  place  of  their  natiu-al  exit  from  the  cranio- 
spmal  cavity.   (After  Bourgery.) 

adherent  to  the  bone,  on  the  outer  surface  also,  is  a  layer  of  endothelial 
cells  very  similar  to  those  found  in  serous  membranes.    (2.)  The  Arach- 


90 


HAND-BOOK  OF  PHYSIOLOGY. 


noid  is  a  much  more  delicate  membrane  very  similar  in  structure  to  the 
dura  mater,  and  lined  on  its  outer  or  free  surface  by  an  endothelial  mem- 
brane. (3.)  The  Pia  Mater  consists  of  two  chief  layers  between  which 
numerous  blood-vessels  ramify.  Between  the  arachnoid  and  pia  mater 
is  a  network  of  fibrous-tissue  trabecul^e  sheathed  with  endothelial  cells: 
these  sub-arachnoid  trabecule  divide  up  the  sub -arachnoid  space  into  a 
number  of  irregular  sinuses.  There  are  some  similar  trabeculae,  but 
much  fewer  in  number,  traversing  the  sub-dural  space,  i.e.,  the  space 
between  the  dura  mater  and  arachnoid. 

^^Pacchionian"  bodies  are  growths  from  the  sub-arachnoid  network 
of  connective-tissue  trabeculse  which  project  through  small  holes  in  the 
inner  layers  of  the  dura  mater  into  the  venous  sinuses  of  that  membrane. 
The  venous  sinuses  of  the  dura  mater  have  been  injected  from  the  sub- 
arachnoidal space  through  the  intermediation  of  these  villous  outgrowths 
known  as  ^'Pacchionian  bodies.''^ 

The  Spinal  Cord  A25"d  its  Neeyes. 

The  Spinal  cord  is  a  cylindriform  column  of  nerve-substance  con- 
nected above  with  the  brain  through  the  medium  of  the  medulla  oblon- 
gata, and  terminating  below,  about  the  lower  border  of  the  first  lumbar 
vertebra,  in  a  slender  filament  of  grey  substance,  the  Jilu?n  term  inale, 
which  lies  in  the  midst  of  the  roots  of  many  nerves  forming  the  cauda 
equina. 

Structure. — The  cord  is  composed  of  white  and  grey  nervous  sub- 
stance, of  which  the  former  is  situated  externally,  and  constitutes  its  chief 
portion,  while  the  latter  occupies  its  central  or  axial  portion,  and  is  so 
arranged,  that  on  the  surface  of  a  transverse  section  of  the  cord  it  appears 
like  two  somewhat  crescentic  masses  connected  together  by  a  narrower  por- 
tion or  isthmus  (Fig.  318).  Passing  through  the  centre  of  this  isthmus 
in  a  longitudinal  direction  is  a  minute  canal  (central  canal),  which  is 
continued  through  the  wdiole  length  of  the  cord,  and  opens  above  into 
the  space  at  the  back  of  medulla  oblongata  and  pons  Varolii,  called  the 
fourth  ventricle.    It  is  lined  by  a  layer  of  columnar  ciliated  epithelium. 

The  spinal  cord  consists  of  two  exactly  symmetrical  halves  separated 
anteriorly  and  posteriorly  by  Yerticuljissni^es  (the  posterior  fissure  being 
deeper,  but  less  wide  and  distinct  than  the  anterior),  and  united  in  the 
middle  by  nervous  matter  wdiich  is  usually  described  as  forming  two  com- 
missures— an  anterior  commissure,  in  front  of  the  central  canal,  consisting 
of  medullated  nerve  fibres,  and  a  posterior  commissure  behind  the  central 
canal,  consisting  also  of  medullated  nerve-fibres,  but  with  more  neuroglia, 
which  gives  the  grey  aspect  to  this  commissure  (Fig.  31 G,  b).  Each  half 
of  the  spinal  cord  is  marked  on  the  sides  (obscurely  at  the  lower  part, 
but  distinctly  above)  by  two  longitudinal  furrows,  which  divide  it  into 


THE  NERVOUS  SYSTEM. 


91 


three  portions,  columns,  or  tracts,  an  anterior,  lateral,  and  posterior.  From 
the  groove  between  the  anterior  and  lateral  columns  spring  the  anterior 
roots  of  the  spinal  nerves  (b  and  c,  5);  and  just  in  front  of  the  groove 
between  the  lateral  and  posterior  column  arise  the  posterior  roots  of  the 
same  (b,  6) :  a  pair  of  roots  on  each  side  corresponding  to  each  vertebra 
(Fig.  317). 

White  matter. — The  white  matter  of  the  cord  is  made  up  of  medullated 
nerve  fibres,  of  various  sizes,  arranged  longitudinally  around  the  cord  under 


Fig.  316.— Different  views  of  a  portion  of  the  spinal  cord  from  the  cerAdcal  region,  with  the  roots 
of  the  nerves  (slightly  enlarged).  In  a,  the  anterior  surface  of  the  specimen  is  shown;  the  anterior 
nerve-root  of  its  right  side  being  divided;  in  b,  a  view  of  the  right  side  is  given;  in  c,  the  upper  sur- 
face is  shown;  in  d,  the  nerve-roots  and  ganglion  are  shown  from  below.  1.  The  anterior  median  fis- 
sure; 2,  posterior  median  fissure;  3,  anterior  lateral  depression,  over  which  the  anterior  nerve-roots 
are  seen  to  spread;  4,  posterior  lateral  groove,  into  which  the  posterior  roots  are  seen  to  sink;  5, 
anterior  roots  passing  the  ganglion;  5',  in  a,  the  anterior  root  divided  ;  6,  the  posterior  roots,  the 
fibres  of  which  pass  into  the  ganglion  6' ;  7,  the  united  or  compound  nerve;  7',  the  posterior  primary- 
branch,  seen  in  a  and  d  to  be  derived  in  part  from  the  anterior  and  in  part  from  the  posterior  root. 
(Allen  Thomson.) 

the  pia  mater  and  passing  in  to  support  the  individual  fibres  in  the  delicate 
connective  tissue  or  neuroglia  made  up  of  a  very  fine  reticulum,  with  both 
small  cells  almost  filled  up  by  nuclei  and  stellate,  branching  corpuscles. 

Size. — The  general  rule  respecting  the  size  of  different  parts  of  the 
cord  appears  to  be,  that  the  size  of  each  part  bears  a  direct  proportion 
to  the  size  and  number  of  nerve-roots  given  off  from  itself,  and  has  but 
little  relation  to  the  size  or  number  of  those  given  off  below  it.  Thus 
the  cord  is  very  large  in  the  middle  and  lower  part  of  its  cervical  portion, 
whence  arise  the  large  nerve-roots  for  the  formation  of  the  brachial' plex- 
uses and  the  supply  of  the  upper  extremities,  and  again  enlarges  at  the  low- 
est part  of  its  dorsal  portion  and  the  upper  part  of  its  lumbar,  at  the  origins 


92 


HAND-BOOK  OF  PHYSIOLOGY. 


of  the  large  nerves  which,  after  forming  the  lumbar  and  sacral  plexuses, 
are  distributed  to  the  lower  extremities.  The  chief  cause  of  the  greater 
size  at  these  parts  of  the  spinal  cord  is  increase  in  the  quantity  of  grey 
matter;  for  there  seems  reason  to  believe  that  the  white  or  fibrous  part 
of  the  cord  becomes  graduall}^  and  progressively  larger  from  below  upward, 
doubtless  from  the  addition  of  a  certain  number  of  upward  passing  fibres 
from  each  pair  of  nerves. 

From  careful  estimates  of  the  number  of  nerve-fibres  in  a  transverse 
section  of  the  cord  toward  its  upper  end,  and  the  number  entering  it 
by  the  anterior  and  posterior  roots  of  each  pair  of  nerves,  it  has  been 


I 


Fig.  317. — Section  of  grey  matter  of  anterior  cornu  of  a  calf 's  spinal  cord:  n  f.  nerve-fibres  of 
white  matter  in  transvei-se  section,  showing  axis-cj-linder  in  centre  of  each:  a  r.  anterior  roots  of 
spinal  nerve  passing  out  though  white  matter;  </ e,  large  stellate  nerve-cells  with  nuclei:  they  are 
seen  imbedded  in  neuroglia.  (.Schofield.) 

shown  that  in  the  numan  spinal  cord  not  more  than  half  of  the  total  num- 
ber of  nerve-fibres  entering  the  cord  through  all  the  spinal  nerves  are  con- 
tained in  a  transverse  section  near  its  upper  end.  It  is  obvious,  therefore, 
that  at  least  half  of  the  nerve-fibres  entering  it  must  terminate  in  the  cord 
itself. 

Grey  matter. — The  grey  matter  of  the  cord  consists  essentially  of  an 
extremely  delicate  network  of  the  primitive  fibrillin  of  axis-cylinders, 
and  which  are  derived  from  the  ramification  of  multipolar  ganglion  cells 
of  very  large  size,  containing  large  round  nuclei  with  nucleoli.  This 
fine  plexus  is  called  Gerlaclis  networh,  and  is  mingled  with  the  meshes 
of  neuroglia,  which  in  some  parts  is  chiefly  fibrillated,  in  others  mainly 
granular  and  punctiform.  The  neuroglia  is  prolonged  from  the  surface 
into  the  tip  of  the  posterior  cornu  of  grey  matter  and  forms  a  jelly-like 
transparent  substance,  which  when  hardened  is  found  to  be  reticular,  and 
is  call(Ml  tlio  sNhstantia  qeJatinosa  of  Rolando. 


THE  NERVOUS  SYSTEM. 


93 


The  multipolar  cells  are  either  scattered  singly  or  arranged  in  groups,  of 
which  the  following  are  to  be  distinguished: — (a.)  In  the  anterior  coniu. 
The  groups  found  in  the  anterior  cornu  are  generally  two — one  at  the 
lateral  part  near  tha  lateral  column,  and  the  other  at  the  tip  of  the  cornu 
in  the  middle  line — sometimes,  as  in  the  lumbar  enlargement,  there  is  a 
third  group  more  posterior.  The  cells  of  the  anterior  group  are  the 
largest.  Into  many  of  these  cells  the  fibres  of  the  anterior  motor  nerve- 
roots  can  be  distinctly  traced,  (b.)  In  the  tractus  intermedio-lateralis, 
A  group  of  nerve-cells  midway  between  the  anterior  and  posterior  cornua, 
near  the  external  surface  of  the  grey  matter.  It  is  especially  developed 
in  the  dorsal  and  also  in  the  upper  cervical  region,    {c. )  In  the  posterior 


Fig.  318.— Transverse  section  of  half  the  spinal  cord  in  the  Ivunbar  enlargement  (semi-diagramma- 
tic). 1.  Anterior  median  fissure;  2,  posterior  median  fissm-e;  3,  central  canal  lined  with  epitheUum; 
4,  posterior  commissure;  .5,  anterior  commissure;  6,  posterior  column;  7,  lateral  column;  8,  anterior 
column.  The  white  substance  is  traversed  by  radiating  trabecule  of  pia  mater.  9.  Fasciculus  of 
posterior  nerve-root  entering  in  one  bxmdle ;  10,  fasciculi  of  anterior  roots  entering  in  four  spreading 
bundles  of  fibres;  6,  in  the  cervix  cornu,  decussating  fibres  from  the  nerve-roots  and  posterior  com- 
missure; c,  posterior  vesicular  columns  of  Lockhart  Clarke.  About  half  way  between  the  central 
canal  and  7  are  seen  the  group  of  nerve-cells  forming  the  tractus  intermedio-lateralis;  e,  e,  fibres  of 
anterior  roots;  e',  fibres  of  anterior  roots  which  decussate  in  anterior  commissure.  (Allen  Thom- 
son.)  X  6. 

vesicular  columns  of  Lockhart  Clark.  These  are  found  in  the  posterior 
cornua  of  grey  matter  toward  the  inner  surface,  extending  from  the  cer- 
vical enlargement  to  the  third  lumbar  nerves  (Fig.  318,  c).  (d.)  Smaller 
cells  are  scattered  throughout  the  grey  matter,  but  are  found  chiefly  at 
the  tip  (caput  cornu)  of  the  posterior  cornu,  in  a  finely  granular  basis, 
and  among  the  posterior  root  fibres  (substantia  gelatinosa  cinerea  of 
Rolando). 

The  nerve-cells  are  connected  by  their  processes  immediately  with  the 
axis-cylinder  of  the  fibres  of  the  anterior  or  motor  nerve-roots:  whereas 
the  nerve-cells  of  the  posterior  roots  are  connected  with  nerve-fibres,  not 


94  HAKD-BOOK  OF  PHYSIOLOGY. 

directly,  but  only  through  the  intermediation  of  Gerlach's  nerve-network, 
in  which  their  branching  processes  lose  themselves. 

Spinal  Nerves. — The  spinal  nerves  consist  of  thirtj^-one  pairs, 
issuing  from  the  sides  of  the  whole  lengtli  of  the  cord,  their  number  corre- 
sponding with  the  intervertebral  foramina  through  which  they  pass. 
Each  nerve  arises  by  two  roots,  an  anterior  and  posterior,  the  latter  being 
the  larger.  The  roots  emerge  through  separate  apertures  of  the  sheath  of 
dura  mater  surrounding  the  cord;  and  directly  after  tlieir  emergence,  where 
the  roots  lie  in  the  intervertebral  foramen,  a  ganglion  is  found  on  the  pos- 
terior root.  The  anterior  root  lies  in  contact  with  the  anterior  surface  of 
the  ganglion,  but  none  of  its  fibres  intermingle  with  those  in  the  gan- 
glion (5,  Fig.  316).  But  immediately  beyond  the  ganglion  the  two  roots 
coalesce,  and  by  the  mingling  of  their  fibres  form  a  compound  or  mixed 
spinal  nerve,  which,  after  issuing  from  the  intervertebral  canal,  divides 
into  an  anterior  and  posterior  branch,  each  containing  fibres  from  both 
the  roots  (Fig.  316). 

The  anterior  root  of  each  spinal  nerve  arises  by  numerous  separate  and 
converging  bundles  from  the  anterior  column  of  the  cord;  the  posterior 
root  by  more  numerous  parallel  bundles,  from  the  posterior  column,  or, 
rather,  from  the  posterior  part  of  the  lateral  column  (Fig.  318),  for  if  a  fis- 
sure be  directed  inward  from  the  gTOOve  between  the  middle  and  pos- 
terior columns,  the  posterior  roots  will  remain  attached  to  the  former. 
The  anterior  roots  of  each  spinal  nerve  consist  of  centrifugal  fibres;  the 
posterior  as  exclusively  of  centripetal  fibres. 

Course  of  the  Fibres  of  the  Spinal  Nerves. — {a)  The  Anterior 
roots  enter  the  cord  in  several  bundles  -R^icli  may  be  called: — (1)  Inter- 
nal; (2)  Middle;  (3)  External;  all  being  more  or  less  connected  with  the 
groups  of  multipolar  cells  in  the  anterior  cornua.  1.  The  internal  fibres 
are  partly  connected  with  internal  gi'oup  of  nerve  cells  of  anterior  cornu 
of  the  same  side;  but  some  fibres  pass  over,  through  anterior  commissure, 
to  end  in  the  anterior  cornu  of  opposite  side,  probably  in  internal  group 
of  cells.  2.  The  middle  fibres  are  partly  in  connection  with  the  lateral 
group  of  cells  in  anterior  cornu,  and  in  part,  pass  backward  to  posterior 
cornu,  having  no  connection  with  cells.  3.  The  external  fibres  are  partly 
in  connection  with  the  lateral  group  of  cells  in  the  anterior  cornu,  but 
some  fibres  proceed  direct  into  the  lateral  column  without  connection  with 
cells  and  pass  upward  in  it. 

{h)  Tlie  Posterior  roots  enter  the  posterior  cornu  in  two  chief  bundles, 
either  at  the  tip,  through  or  round  the  substantia  gclatinosa,  or  by  the 
inner  side.  Tlie  former  enter  the  grey  matter  at  once,  and  as  a  rule,  turn 
upward  or  downward  for  a  certain  distance  and  then  pass  horizontally, 
some  fibres  reach  the  anterior  cornua,  passing  at  once  horizontally;  and 
the  others,  the  opposite  side,  through  the  posterior  grey  commissure.  Of 
those  which  enter  by  the  inner  side  of  the  cornua  the  majority  pass  up 


THE  NERVOUS  SYSTEM. 


95 


(or  down)  in  the  white  substance  of  the  posterior  columns,  and  enter  the 
grey  matter  at  various  heights  at  the  base  of  the  posterior  cornu,  perhaps 
some  pass  directly  upward  without  entering  the  grey  matter.  Those  that 
enter  the  grey  matter  pass  in  various  directions,  some  to  join  the  lateral 
cells  in  the  anterior  cornu,  some  join  the  cells  in  the  posterior  vesicular 
column,  and  some  pass  across  to  the  other  side  of  the  cord  in  the  anterior 
commissure,  whilst  others  become  again  longitudinal  in  the  grey  matter. 

It  should  be  here  mentioned  that  the  cells  in  the  posterior  vesicular 
column  are  connected  with  medullated  fibres  which  pass  horizontally  to 
the  white  matter  of  the  lateral  columns  and  there  become  longitudinal. 

Course  of  tlie  fibres  in  the  cord.  -The  nerve  fibres  which  form  the 
white  matter  of  the  cord  are  nearly  all  longitudinal  fibres.  It  is,  however, 
a  matter  of  great  difiiculty  to  trace  these  fibres  by  mere  dissection,  and  so 
some  other  methods  must  be  adopted.    One  method  is  based  upon  the  fact 


Fig.  319.— Diagram  of  the  spinal  cord  at  the  lower  cervical  region  to  show  the  track  of  fibres; 
d.p.  direct  pyramidal  tract;  c.  %>.  t.,  crossed  pyramidal  tract;  *  direct  cerebellar  tract;  p.  m.  c, 
posterior  medium  column.  (Gowers.) 

that  nerve  fibres  undergo  degeneration  when  they  are  cut  off  from  the 
centre  with  which  they  are  connected,  or  when  the  parts  to  which  they 
are  distributed  are  removed,  as  in  amputation  of  a  limb;  and  information 
as  to  the  course  of  the  fibres  has  been  obtained  by  tracing  the  course  of 
these  degenerated  tracts.  The  second  method  consists  in  observing  the 
development  of  the  various  tracts;  some  have  their  medullary  substance 
later  than  others,  and  are  to  be  distinguished  by  their  more  grey  appear- 
ance. The  chief  tracts  which  have  been  made  out  are  the  following: — 
(1)  The  direct  pyramidal  tract  (Fig.  319  d.p.t.),  a  comparatively  small 
portion  of  the  inner  part  of  the  anterior  columns,  which  is  traceable  from 
the  anterior  pyramids  of  the  medulla  to  the  mid-dorsal  region  of  the  spinal 
cord.  It  consists  of  the  fibres  of  the  pyramids  which  do  not  undergo 
decussation  in  the  medulla.  There  is  reason  for  believing,  however^ 
that  these  fibres  of  the  direct  pyramidal  tract  undergo  decussation  through- 
out their  course,  and  fibres  pass  over  through  the  anterioi;  commissure 
to  join  the  lateral  pyramidal  tract  {vide  infra)\  (2)  the  Crossed  pyra- 
midal tract  (Fig.  319,  c.jy.t.)  can  be  traced  from  the  anterior  pyramids 


96 


HAND-BOOK  OF  PHYSIOLOGY. 


of  the  medulla,  and  consists  of  fibres  which  decussate  in  the  anterior  fis- 
sure and  pass  downward  in  the  lateral  columns  near  the  posterior  cornu 
of  the  grey  matter  to  the  lower  end  of  the  cord;  (3)  Direct  cerebellar 
tract  (Fig.  319),  which  corresponds  to  the  peripheral  portion  of  the  pos- 
terior lateral  column  between  the  crossed  pyramidal  tract  and  the  edge 
of  the  cord,  can  be  traced  up  directly  to  the  cerebellum  and  down  to 
the  mid-lumbar  region;  (4).  Posterior  mediu?n  column,  or  Fasciculus 
of  Goll,  is  found  on  either  side  of  the  posterior  commissure,  and  is  trace- 
able upward  as  the  fasciculus  gracilis  of  the  medulla,  the  fibres  are  con- 
nected with  the  cells  of  the  posterior  vesicular  column.  It  is  traceable 
downward  to  the  mid -dorsal  region.  As  regards  the  remaining  part  of 
the  cord  unoccupied  by  the  above  tracts  little  can  be  said.  The  portion 
of  the  posterior  column  between  the  posterior  median  column  and  the 
posterior  roots  of  the  spinal  nerves,  known  as  fascictilus  cuneatus  or  Bur- 
dach's  column,  is  composed  of  fibres  of  the  posterior  roots  on  their  way  to 
enter  the  grey  substance  at  different  heights.  The  antero-lateral  column 
contains  fibres  from  the  anterior  cornua  of  the  same  as  well  as  of  the  op~ 
posite  side. 

Functions  of  the  Spinal  Nerves. — The  anterior  spinal  nerve-roots 
are  efferent  or  motor:  the  posterior  are  afferent  or  sensory  (Sir.  C.  Bell). 
The  fact  is  proved  in  various  ways.  Division  of  the  anterior  roots  of 
one  or  more  nerves  is  followed  by  complete  loss  of  motion  in  the  parts 
supplied  by  the  fibres  of  such  roots;  but  the  sensation  of  the  same  parts 
remains  perfect.  Division  of  the  posterior  roots  destroys  the  sensibility 
of  the  parts  supplied  by  their  fibres,  while  the  power  of  motion  continues 
unimpaired.  Moreover,  irritation  of  the  ends  of  the  distal  portions  of  the 
divided  anterior  roots  of  a  nerve  excites  muscular  movements;  irritation  of 
the  ends  of  the  proximal  portions,  which  are  still  in  connection  of  the 
cord,  is  followed  by  no  appreciable  effect.  Irritation  of  the  distal  portions 
of  the  divided  posterior  roots,  on  the  other  hand,  produces  no  muscular 
movements  and  no  manifestations  of  pain;  for,  as  already  stated,  sensory 
nerves  convey  impressions  only  toward  the  nervous  centres:  but  irritation 
of  the  proximal  portions  of  these  roots  elicits  signs  of  intense  suffering. 
Occasionally,  under  this  last  irritation,  muscular  movements  also  ensue; 
but  these  are  either  voluntary,  or  the  result  of  the  irritation  being  reflected 
from  the  sensory  to  the  motor  fibres.  Occasionally,  too,  irritation  of  the 
distal  ends  of  divided  anterior  roots  elicits  signs  of  pain,  as  well  as  produ- 
cing muscular  movements:  the  pain  thus  excited  is  probably  the  result 
either  of  cramp  or  of  so-called  recurrent  sensibility  (Brown-Sequard). 

Recurrent  Sensibility. — If  the  anterior  root  of  a  spinal  nerve  be  di- 
vided and  tlie  peripheral  end  be  irritated,  not  only  movements  of  the 
muscles  supplied  by  the  nerve  take  place,  but  also  of  other  muscles,  in- 
dicative of  pain.  If  the  main  trunk  of  tlio  nerve  (after  the  coalescence  of 
the  roots  beyond  the  ganglion)  be  divided,  and  the  anterior  root  be  irri- 


THE  NERVOUS  SYSTEM. 


97 


tated  as  before,  th3  general  signs  of  pain  still  remain,  although  the  con- 
traction of  the  muscles  does  not  occur.  The  signs  of  pain  disappear  when 
the  posterior  root  is  divided.  From  these  experiments  it  is  believed  that 
the  stimulus  passes  down  the  anterior  root  to  the  mixed  nerve  and  returns 
to  the  central  nervous  system  through  the  posterior  root  by  means  of  cer- 
tain sensory  fibres  from  the  posterior  root,  which  loop  back  into  the  ante- 
rior root,  before  cont'riuing  their  course  into  the  mixed  nerve-trunk. 

Functions  of  the  Ganglia  on  Posterior  Roots. — The  ganglia  act 
as  centres  for  the  nutrition  of  the  nerves,  since  when  the  nerves  are  severed 
from  connection  with  the  ganglia,  the  parts  Of  the  nerves  so  severed 
degenerate,  whilst  the  parts  which  remain  in  connection  with  them  do  not. 

Fuiq"CTIOiq"S  OF  THE  SPIl^'AL  OOED. 

The  power  of  the  spinal  cord,  as  a  nerve-centre,  may  be  arranged  under 
the  heads  of  (1)  Conduction;  (2)  Transference;  (3)  Eeflex  action. 

(1)  Conduction. — The  funijtions  of  the  S23inal  cord  in  relation  to  con-^ 
dudion  may  be  best  remembered  by  considering  its  anatomical  connections 
with  other  parts  of  the  body.  From  these  it  is  evident  that,  with  the  ex- 
ception of  some  few  filaments  of  the  sympathetic,  there  is  no  way  by 
which  nerve-impulses  can  be  conveyed  from  the  trunk  and  extremities  to 
the  brain  or  vice  versa,  other  than  that  formed  by  the  spinal  cord. 
Through  it,  the  impressions  made  upon  the  peripheral  extremities  or  other 
parts  of  the  spinal  sensory  nerves  are  conducted  to  the  brain,  where  alone 
they  can  be  jjerceived.  Through  it,  also,  the  stimulus  of  the  will,  con- 
ducted from  the  brain,  is  capable  of  exciting  the  action  of  the  muscles 
supplied  from  it  with  motor  nerves.  And  for  all  these  conductions  of 
impressions  to  and  fro  between  the  brain  and  the  spinal  nerves,  the  per- 
fect state  of  the  cord  is  necessary;  for  when  any  part  of  it  is  destroyed, 
and  its  communication  with  the  brain  is  interrupted,  impressions  on  the 
sensory  nerves  given  off  from  it  below  the  seat  of  injury,  cease  to  be 
propagated  to  the  brain,  and  the  brain  loses  the  power  of  voluntarily 
exciting  the  motor  nerves  proceeding  from  the  portion  of  cord  isolated 
from  it.  Illustrations  of  this  are  furnished  by  various  examples  of  paraly- 
sis, but  by  none  better  than  by  the  common  paraplegia,  or  loss  of  sensa- 
tion and  voluntary  motion  in  the  lower  part  of  the  body,  in  consequence^, 
of  destructive  disease  or  injury  of  a  portion,  including  the  whole  thick- 
ness, of  the  spinal  cord.  Such  lesions  destroy  the  communication  be- 
tween the  brain  and  all  parts  of  the  spinal  cord  below  the  seat  of  injury, 
and  consequently  cut  off  from  their  connection  with  the  brain  the  various, 
organs  supplied  with  nerves  issuing  from  those  parts  of  the  cord. 

It  is  probable  that  the  conduction  of  impressions  along  the  cord  is; 
effected  (at  least,  for  the  most  part)  through  the  grey  substance,  i.e.,, 
through  the  nerve -corpuscles  and  filaments  connecting  them.    But  all  parts; 
Vol.  II.— 7. 


98 


HAOT-BOOK  OF  PHYSIOLOGY. 


of  tlie  cord  are  not  alike  able  to  conduct  all  impressions;  and  as  there  are 
separate  nerve-fibres  for  motor  and  for  sensory  impressions,  so  in  the  cord, 
separate  and  determinate  parts  serve  to  conduct  always  the  same  kind  of 
impression. 

Experiments  (chiefly  by  Brown-Sequard),  point  to  the  following  con- 
clusions regarding  the  conduction  of  sensory  and  motor  impressions 
through  the  spinal  cord. 

It  is  important  to  bear  in  mind  that  the  grey  matter  of  the  cord, 
though  it  conducts  impressions  giving  rise  to  sensation,  appears  not  to  be 
sensitive  when  it  is  directly  stimulated.    The  explanation  probably  is, 


Fia.  320.— Diagram  of  the  decussation  of  the  conductors  for  voluntary  movements,  and  those  for 
sensation:  a,  r,  anterior  roots  and  their  continuations  in  the  spinal  cord,  and  decussation  at  the 
lower  part  of  the  medulla  oblongata,  m  o;  p  r,  the  posterior  roots  and  their  continuation  and  decus- 
sation in  the  spinal  cord;  gf  (7,  the  ganglions  of  the  roots.  The  arrows  indicate  the  direction  of  the 
nervous  action;  r,  the  right' side;  I,  the  left  side.  1,  2,  3,  indicate  jalaces  of  alteration  in  a  lateralhalf 
of  the  spino-cerebral  axis,  to  show  the  influence  on  the  two  kinds  of  conduc*"  resulting  from  sec- 
tion of  the  cord  at  any  one  of  these  three  places.   (After  Brown-S6quard.) 


that  it  possesses  no  apparatus  such  as  exists  at  the  peripheral  terminations 
of  sensory  nerves,  for  the  reception  of  sensory  impressions. 

a.  Sensory  impressions,  conveyed  to  the  spinal  cord  by  root-fibres  of 
the  posterior  nerves  are  not  conducted  to  the  brain  only  by  the  posterior 
columns  of  the  cord,  but  pass  through  them  in  great  part  into  tlic  central 
grey  substance,  by  which  they  are  transmitted  to  the  brain  {p  v.  Fig.  320). 

b.  The  impressions  thus  conveyed  to  the  grey  substance  do  not  pass 
up  to  the  brain  to  more  than  a  slight  degree,  along  that  half  of  the  cord 
corresponding  to  the  side  from  wliich  tliey  have  been  received,  but  cross 


I 


THE  NERVOUS  SYSTEM. 


99 


over  to  the  other  side  almost  immediately  after  entering  the  cord,  and 
along  it  are  transmitted  to  the  brain.  There  is  thus,  in  the  cord  itself, 
an  almost  complete  decussation  of  sensory  impressions  brought  to  it;  so 
that  division  or  disease  of  one  posterior  half  of  the  cord  (3,  Fig.  320)  is 
followed  by  loss  of  sensation,  not  in  parts  on  the  corresponding,  but  in 
those  of  the  opposite  side  of  the  body.  From  the  same  fact  it  happens 
that  a  longitudinal  antero-posterior  section  of  the  cord,  along  its  whole 
length,  most  completely  abolishes  sensibility  on  both  sides  of  the  body. 

c.  The  various  sensations  of  touch,  pain,  temperature,  and  muscular 
contraction,  are  probably  conducted  along  separate  and  distinct  sets  of 
fibres.  All,  however,  with  the  exception  of  the  last  named,  undergo  decus- 
sation in  the  spinal  cord. 

d.  The  posterior  columns  of  the  cord  appear  to  have  a  great  share  in 
reflex  movements. 

e.  Impulses  of  the  will,  leading  to  voluntary  contractions  of  muscles, 
appear  to  be  transmitted  principally  along  the  antero -lateral  columns; 
but  if  a  transverse  section  of  this  part  be  made  (the  grey  matter  being  in- 
tact) although  at  first  no  voluntary  movements  of  the  part  below  occur, 
this  paralysis  is  only  temporary,  indicating  that  the  grey  matter  may  take 
on  the  conduction  of  these  impulses. 

/.  Decussation  of  motor  impulses  occurs,  not  in  the  spinal  cord,  as  is 
the  case  with  sensory  impressions,  but  at  the  anterior  part  of  the  medulla 
oblongata  (Fig.  321).  Hence,  motor  impulses,  having  made  their  decus- 
sation, first  enter  the  cord  by  the  lateral  tracts  and  adjoining  grey  matter, 
and  then  pass  to  the  anterior  columns  and  to  the  grey  matter  associated 
with  them.  Accordingly,  division  of  the  anterior  pyramids,  at  the  point 
of  decussation  (2,  Fig.  320),  is  followed  by  paralysis  of  motion  in  all  parts 
below;  while  division  of  the  olivary  bodies  which  constitute  the  true  con- 
tinuations of  the  anterior  columns  of  the  cord,  appears  to  produce  very 
little  paralysis.  Disease  or  division  of  any  part  of  the  cerebro-spinal  axis 
above  the  seat  of  decussation  (1,  Fig.  320)  is  followed,  as  well-known, 
by  impaired  or  lost  power  of  motion  on  the  opposite  side  of  the  body; 
while  a  like  injury  inflicted  below  this  part  (3,  Fig.  320),  induces  similar 
paralysis  on  the  corresponding  side. 

When  one  half  of  the  spinal  cord  is  cut  through,  complete  anaesthesia 
of  the  other  side  of  the  body  below  the  point  of  section  results,  but  there 
is  often  greatly  increased  sensibility  (hyperaesthesia)  on  the  same  side;  so 
much  so  that  the  least  touch  appears  to  be  agonizing.  This  condition 
may  persist  for  several  days.  Similar  effects  may,  in  man,  be  the  result 
of  injury.  Thus,  in  a  patient  who  had  sustained  a  severe  lesion  of  the 
spinal  cord  in  the  cervical  region,  causing  extensive  paralysis  and  loss  of 
sensation  in  the  lower  half  of  the  body,  there  were  two  circumscribed 
areas,  one  on  each  arm,  symmetrically  placed,  in  which  the  gentlest  touch 
caused  extreme  pain. 


100 


HAND-BOOK  OF  PHYSIOLOGY. 


In  addition  to  the  transmission  of  ordinary  sensory  and  motor  im- 
pulses, the  spinal  cord  is  the  medium  of  conduction  also  of  impulses  to 
and  from  the  vaso-motor  centre  in  the  medulla  oblongata,  and  probably 
also  contains  special  vaso-motor  centres. 

2.  Transference. — Examples  of  the  transference  of  impressions  in 
the  cord  have  been  given  (p.  84,  Vol.  II.);  and  that  the  transference 
takes  place  in  the  cord,  and  not  in  the  brain,  is  nearly  proved  by  the  fre- 
quent cases  of  pain  felt  in  the  knee  and  not  in  the  hip,  in  diseases  of  the 
hip;  of  pain  felt  in  the  urethra  or  gians  penis,  and  not  in  the  bladder,  in 
calculus;  for,  if  both  the  primary  and  the  secondary  or  transferred  im- 
pression were  in  the  brain,  both  should  be  felt. 

3.  Reflection. — In  man  the  spinal  cord  is  so  much  under  the  control 
of  the  higher  nerve-centres,  that  its  own  individual  functions  in  relation 
to  reflex  action  are  apt  to  be  overlooked;  so  that  the  result  of  injury,  by 
which  the  cord  is  cut  off  completely  from  the  influence  of  the  encephalon, 
is  apt  to  lessen  rather  than  increase  our  estimate  of  its  importance  and 
individual  endowments.  Thus,  when  the  human  spinal  cord  is  divided, 
the  lower  extremities  fall  into  any  position  that  their  weight  and  the 
resistance  of  surrounding  objects  combine  to  give  them;  if  the  body  is 
irritated,  they  do  not  move  toward  the  irritation;  and  if  they  are  touched, 
the  consequent  reflex  movements  are  disorderly  and  purposeless;  all  power 
of  voluntary  movement  is  absolutely  abolished.  In  other  mammals,  e.g., 
rabbit  or  dog,  after  recovery  from  the  shock  of  the  operation,  which  takes 
some  time,  reflex  actions  in  the  parts  below  Avill  occur  after  the  spinal 
cord  has  been  divided,  a  very  feeble  irritation  being  followed  by  extensive 
and  co-ordinate  movements.  In  the  case  of  the  frog,  however,  and  many 
other  cold-blooded  animals,  in  which  experimental  and  other  injuries  of 
the  nerve-tissues  are  better  borne,  and  in  which  the  lower  nerve-centres 
are  less  subordinate  in  their  action  to  the  higher,  the  reflex  functions  of 
the  cord  are  still  more  clearly  shown.  When,  for  example,  a  frog's  head 
is  cut  ofl,  the  limbs  remain  in  or  assume  a  natural  position;  they  resume 
it  when  disturbed;  and  when  the  abdomen  or  back  is  irritated,  the  feet 
are  moved  with  the  manifest  purpose  of  pushing  away  the  irritation. 
The  main  difference  in  the  cold-blooded  animals  being  that  the  reflex 
movements  are  more  definite,  complicated,  and  effective,  although  less 
energetic  than  in  the  case  of  mammals.  It  is  as  if  the  mind  of  the  animal 
were  still  engaged  in  the  acts;  and  yet  all  analogy  Avould  lead  us  to  the 
belief  that  the  spinal  cord  of  the  frog  has  no  different  endowment,  in 
hind,  from  those  which  belong  to  the  cord  of  the  higher  vertebrata:  the 
difference  is  only  in  degree.  And  if  this  be  granted,  it  may  bo  assumed 
that,  in  man  and  the  higher  animals,  many  actions  are  performed  as  reflex 
movements  occurring  through  and  by  means  of  the  spinal  cord,  although 
the  latter  cannot  by  itself  initiate  or  even  direct  them  independently. 

Co-ordinate  Movement  not  a  proof  of  Consciousness. — The 


THE  NERVOUS  SYSTEM. 


101 


evident  adaptation  and  purpose  in  the  movements  of  the  cold-blooded 
animals,  have  led  some  to  think  that  they  must  be  conscious  and  capable 
of  will  without  their  brains.  But  purposive  movements  are  no  proof  of 
consciousness  or  will  in  the  creature  manifesting  them.  The  movements 
of  the  limbs  of  headless  frogs  are  not  more  purposive  than  the 
movements  of  our  own  respiratory  muscles  are;  in  which  we  know  that 
neither  will  nor  consciousness  is  at  all  times  concerned.  It  may  not,  in- 
deed, be  assumed  that  the  acts  of  standing,  leaping,  and  other  move- 
ments, which  decapitated  cold-blooded  animals  can  perform,  are  also 
always,  in  the  entire  and  healthy  state,  performed  involuntarily,  and 
under  the  sole  influence  of  the  cord;  but  it  is  probable  that  such  acts 
may  be,  and  commonly  are,  so  performed,  the  higher  nerve-centres  of  the 
animal  having  only  the  same  kind  of  influence  in  modifying  and  direct- 
ing them,  that  those  of  man  have  in  modifying  and  directing  the  move- 
ments of  the  respiratory  muscles. 

Inhibition  of  Reflex  Actions. — The  fact  that  such  movements  as 
are  produced  by  irritating  the  skin  of  the  lower  extremities  in  the  human 
subject,  after  division  or  disorganization  of  a  part  of  the  spinal  cord,  do 
not  follow  the  same  irritation  when  the  mind  is  active  and  connected 
with  the  cord  through  the  brain,  is,  probably,  due  to  the  mind  ordinarily 
perceiving  the  irritation  and  instantly  controlling  the  muscles  of  the  irri- 
tated and  other  parts;  for,  even  when  the  cord  is  perfect,  such  involun- 
tary movements  will  often  follow  irritation,  if  it  be  applied  when  the  mind 
is  wholly  occupied.  When,  for  example,  one  is  anxiously  thinking,  even 
slight  stimuli  will  produce  involuntary  and  reflex  movements.  So,  also, 
during  sleep,  such  reflex  movements  may  be  observed,  when  the  skin  is 
touched  or  tickled;  for  example,  when  one  touches  with  the  finger  the 
palm  of  the  hand  of  a  sleeping  child,  the  finger  is  grasped — the  impres- 
sion on  the  skill  of  the  palm  producing  a  reflex  movement  of  the  muscles 
which  close  the  hand.  But  when  the  child  is  awake,  no  such  effect  is 
produced  by  a  similar  touch. 

Further,  many  reflex  actions  are  capable  of  being  more  or  less  con- 
trolled or  even  altogether  prevented  by  the  will:  thus  an  inhibitory  slcHoil 
may  be  exercised  by  the  brain  over  reflex  functions  of  the  cord  and  the 
other  nerve  centres.  The  following  may  be  quoted  as  familiar  examples 
of  this  inhibitory  action: — 

To  prevent  the  reflex  action  of  crying  out  when  in  pain,  it  is  often 
sufficient  firmly  to  clench  the  teeth  or  to  grasp  some  object  and  hold  it 
tight.  When  the  feet  are  tickled  we  can,  by  an  effort  of  will,  prevent  the 
reflex  action  of  jerking  them  up.  So,  too,  the  involuntary  closing  of  the 
eyes  and  starting,  when  a  blow  is  aimed  at  the  head,  can  be  similarly 
restrained. 

Darwin  has  mentioned  an  interesting  example  of  the  way  in  which, 
on  the  other  hand,  such  an  instinctive  reflex  act  may  override  the 


102 


HAND-BOOK  OF  PHYSIOLOGY. 


strongest  effort  of  the  will.  He  placed  liis  face  close  against  the  glass  of 
the  cobra's  cage  in  the  Reptile  House  at  the  Zoological  Gardens,  and 
though,  of  course,  thoroughly  convinced  of  his  perfect  security,  could 
not  by  any  effort  of  the  will  prevent  himself  from  starting  back  when 
the  snake  struck  with  fury  at  the  glass. 

It  has  been  found  by  experiment  that  in  a  frog  the  optic  lobes  and 
optic  thalami  have  a  distinct  action  in  inhibiting  or  delaying  reflex  action, 
and  also  that  more  generally  any  afferent  stimulus,  if  sufficiently  strong, 
may  inliibit  or  modify  any  reflex  action  even  in  the  absence  of  these 
centres. 

On  the  whole,  therefore,  it  may,  from  these  and  like  facts,  be  con- 
cluded that  reflex  acts,  performed  under  the  influence  of  the  reflecting 
power  of  the  spinal  cord,  are  essentially  independent  of  the  brain  and 
may  be  performed  perfectly  when  the  brain  is  separated  from  the  cord: 
that  these  include  a  much  larger  number  of  the  natural  and  purposive 
movements  of  the  lower  animals  than  of  the  warm-blooded  animals  and 
man:  and  that  over  nearly  all  of  them  the  mind  may  exercise,  through 
the  higher  nerve  centres,  some  control;  determining,  directing,  hinder- 
ing, or  modifying  them,  either  by  direct  action,  or  by  its  power  over 
associated  muscles. 

To  these  instances  of  spinal  reflex  action,  some  add  yet  many  more,  in- 
cluding nearly  all  the  acts  which  seem  to  be  performed  unconsciously, 
such  as  those  of  walking,  running,  writing,  and  the  like:  for  these  are 
really  involuntary  acts.  It  is  true  that  at  their  first  performances  they 
are  voluntar}",  that  they  require  education  for  their  perfection,  and  are 
at  all  times  so  constantly  performed  in  obedieiice  to  a  mandate  of  tlie 
Tvill,  that  it  is  difficult  to  believe  in  their  essentially  involuntary  nature. 
But  the  will  really  has  only  a  controlling  power  over  their  performance;  it 
can  hasten  or  stay  them,  but  it  has  little  or  nothing  to  do  with  the  actual 
carrying  out  of  the  effect.  And  this  is  proved  by  the  circumstance  that 
these  acts  can  be  performed  with  complete  mental  abstraction:  and,  more 
than  this,  that  the  endeavor  to  carry  them  out  entirely  by  the  exercise 
of  the  will  is  not  only  not  beneficial,  but  positively  interferes  with  their 
harmonious  and  perfect  performance.  Any  one  may  convince  himself  of 
this  fact  by  trying  to  take  each  step  as  a  voluntary  act  in  walking  down 
stairs,  or  to  form  each  letter  or  word  in  writing  by  a  distinct  exercise  of 
the  will. 

These  actions,  however,  will  be  again  referred  to,  when  treating  of 
their  possible  connection  with  the  functions  of  the  so-called  sensory  gan- 
glia, p.  115  et  seq.,  Vol.  II. 

Morbid  rcf  exactions. — The  relation  of  the  reflex  action  to  the  strength 
of  the  stimulus  is  tlie  same  as  was  shown  generally  in  the  action  of  gan- 
glia, a  slight  stiiHuhis  producing  a  slight  (p.  87,  Vol.  II.)  niovement  .  and  a 
greater,  a  greater  movement,  and. so  on;  but  in  instances  in  wliich  we  must 


THE  NERVOUS  SYSTEM. 


103 


assume  that  the  cord  is  morlidly  more  irritable,  i.e.,  apt  to  issue  more  nerv- 
ous force  than  is  proportionate  to  the  stimulus  applied  to  it,  a  slight  impres- 
sion on  a  sensory  nerve  produces  extensive  reflex  movements.  This  appears 
to  be  the  condition  in  tetanus,  in  which  a  slight  touch  on  the  skin  may 
throw  the  whole  body  into  convulsion.  A  similar  state  is  induced  by  the 
introduction  of  strychnia  and,  in  frogs,  of  opium  into  the  blood;  and 
numerous  experiments  on  frogs  thus  made  tetanic,  have  shown  that  the 
tetanus  is  wholly  unconnected  with  the  brain,  and  depends  on  the  state 
induced  in  the  spinal  cord. 

Special  Centres  in  Spinal  Cord. — It  may  seem  to  have  been  im- 
plied that  the  spinal  cord,  as  a  single  nerve-centre,  reflects  alike  from  all 
parts  all  the  impressions  conducted  to  it.  But  it  is  more  probable  that 
it  should  be  regarded  as  a  collection  of  nervous  centres  united  in  a  con- 
tinuous column.  This  is  made  probable  by  the  fact  that  segments  of  the 
cord  may  act  as  distinct  nerve-centres,  and  excite  motions  in  the  parts  sup- 
plied with  nerves  given  off  from  them;  as  well  as  by  the  analogy  of  cer- 
tain cases  in  which  the  muscular  movements  of  single  organs  are  under 
the  control  of  certain  circumscribed  portions  of  the  cord.  Thus, — for 
the  governance  of  the  sphincter- muscles  concerned  in  guarding  the  orifices 
respectively  of  the  rectum  and  urinary  bladder  there  are  special  nerve- 
centres  in  the  lower  part  of  the  spinal  cord  (ano-spinal  and  vesicospinal 
centres);  while  the  actions  of  these  are  temporarily  by  stimuli 

which  lead  to  defascation  and  micturition.  So,  also,  there  are  centres 
directly  concerned  in  erection  of  the  penis  and  in  the  emission  of  semen 
{genito-iirinary).  The  emission  of  semen  is  a  reflex  act:  the  irritation 
of  the  glans  penis  conducted  to  the  spinal  cord,  and  thence  reflected,  ex- 
cites the  successive  and  co-ordinate  contractions  of  the  muscular  fibres  of 
the  vasa  deferentia  and  vesiculge  seminales,  and  of  the  accelerator  urinae 
and  other  muscles  of  the  urethra;  and  a  forcible  expulsion  of  semen  takes 
place,  over  which  the  mind  has  little  or  no  control,  and  which,  in  cases 
of  paraplegia,  may  be  unfelt.  The  erection  of  the  penis,  also,  as  already 
explained  (p.  169,  Vol.  I.),  appears  to  be  in  part  the  result  of  a  reflex  con- 
traction of  the  muscles  by  which  the  veins  returning  the  blood  from  the 
penis  are  compressed.  The  involuntary  action  of  the  uterus  in  expelling 
its  contents  during  parturition,  is  also  of  a  purely  reflex  kind,  dependent 
in  part  upon  the  spinal  cord,  though  in  part  also  upon  the  sympathetic 
system:  its  independence  of  the  brain  being  proved  by  cases  of  delivery  in 
paraplegic  women,  and  also  by  the  fact  that  delivery  can  take  place  whilst 
the  patient  is  under  the  influence  of  chloroform.  But  all  these  spinal 
nerve-centres  are  intimately  connected,  both  structurally  and  physi- 
ologically, one  with  another,  as  well  as  with  those  higher  encephalic 
centres,  without  whose  guiding  influence  their  actions  may  become  dis- 
orderly and  purposeless,  or  altogether  abrogated. 

Centre  for  Movements  of  Lymphatic  Hearts  of  Frog. — Volkmann 


104 


HAND-BOOK  OF  PHYSIOLOGY. 


has  shown  that  the  rhythmical  movements  of  the  anterior  pair  of 
lymphatic  hearts  in  the  frog  depend  upon  nervous  influence  derived  from 
the  portion  of  spinal  cord  corresponding  to  the  third  vertebra,  and  those 
of  the  posterior  pair  on  influence  supplied  by  the  portion  of  cord  opposite 
the  eighth  vertebra.  The  movements  of  the  heart  continue,  though  the 
whole  of  the  cord,  except  the  above  portions,  be  destroyed;  but  on  the 
instant  of  destroying  either  of  these  portions,  though  all  the  rest  of  the 
cord  be  untouched,  the  movements  of  the  corresponding  hearts  cease. 
What  appears  to  be  thus  proved  in  regard  to  two  portions  of  the  cord, 
may  be  inferred  to  prevail  in  other  portions  also;  and  the  inference  is 
reconcilable  with  most  of  the  facts  known  concerning  the  physiology  and 
comparative  anatomy  of  the  cord. 

Tone  of  Muscles. — The  influence  of  the  spinal  cord  on  the  sphinc- 
ter ani  (centre  for  defcecation)  has  been  already  mentioned  (see  above). 
It  maintains  this  muscle  in  permanent  contraction,  so  that,  except  in 
the  act  of  defgecation,  the  orifice  of  the  anus  is  always  closed.  This 
influence  of  the  cord  resembles  its  common  reflex  action  in  being  involun- 
tary, although  the  will  can  act  on  the  muscle  to  make  it  contract  more, 
or  may  inhibit  the  action  of  the  ano-sjoinal  centre  so  as  to  permit  its  dila- 
tation. The  condition  of  the  sphincter  ani,  however,  is  not  altogether 
exceptional.  It  is  the  same  in  kind,  though  it  exceeds  in  degree  that 
condition  of  muscles  which  has  been  called  tone,  or  passive  contraction; 
a  state  in  which  they  always  when  not  active  appear  to  be  during  health, 
and  in  which,  though  called  inactive,  they  are  in  slight  contraction,  and 
certainly  are  not  relaxed,  as  they  are  long  after  death,  or  when  the  spinal 
cord  is  destroyed.  This  tone  of  all  the  muscles  of  the  trunk  and  limbs 
depends  on  the  spinal  cord,  as  the  contraction  of  the  sphincter  ani  does. 
If  an  animal  be  killed  by  injury  or  removal  of  the  brain  the  tone  of  the 
muscles  may  be  felt  and  the  limbs  feel  firm  as  during  sleep;  but  if  the 
spinal  cord  be  destroyed,  the  sphincter  ani  relaxes,  and  all  the  muscles 
feel  loose,  and  flabby,  and  atonic,  and  remain  so  till  rigor  mortis  com- 
mences. This  kind  of  tone  must  be  distinguished  from  that  mere  firm- 
ness and  tension  which  it  is  customary  to  ascribe,  under  the  name  of  tone, 
to  all  tissues  that  feel  robust  and  not  flabby,  as  well  as  to  muscles.  The 
tone  peculiar  to  muscles  has  in  it  a  degree  of  vital  contraction:  that  of 
other  tissues  is  only  due  to  their  being  well  nourished,  and  therefore  com- 
pact and  tense. 

All  the  foregoing  examples  illustrate  the  fact  that  the  spinal  cord  is  a 
collection  of  reflex  centres,  upon  which  the  higher  centres  act  by  sending 
down  impulses  to  set  in  motion,  to  modify  or  to  control  them;  the 
movements  or  other  phenomena  of  reflection  being  as  it  were  the  function 
of  the  ganglion  cells  to  sot  in  action,  after  an  afferent  impression  lias  been 
conveyed  to  them  by  the  posterior  nerve-trunks  in  connection  witli  them. 
The  extent  of  the  resulting  movement  depends  upon  the  strength  of  the 


THE  NERVOUS  SYSTEM. 


105 


stimulus,  the  position  at  which  it  was  applied  as  well  as  upon  the  condi- 
tion of  the  nerve  cells;  the  connection  between  the  cells  being  so  intimate 
that  a  series  of  co-ordinated  movements  may  result  from  a  single  stimula- 
tion, first  of  all  affecting  one  cell.  Whether  the  cells  possess  as  well  the 
power  of  originating  impulses  (automatism)  is  doubtful,  but  this  is  pos- 
sible in  the  case  of  vaso-niotor  centres  which  are  situated  in  the  cord  (p. 
154,  Vol.  I.),  and  of  siueating  centres  which  must  be  closely  related  to 
them,  and  possibly  in  the  case  of  the  centres  for  maintaining  the  tone  of 
muscles. 

The  Medulla  Oblon^gata. 

The  medulla  oblongata  (Figs.  321,  322),  is  a  column  of  grey  and  white 
nervous  substance  formed  by  the  prolongation  upward  of  the  spinal  cord 
and  connecting  it  with  the  brain. 


Fig.  321.  Fig.  322. 


Fig.  321. — Anterior  surface  of  the  pons  Varolii,  and  medulla  oblongata,  a,  a,  anterior  pyramids; 
6,  their  decussation;  c,  c,  olivary  bodies;  d,  cZ,  restiform  bodies;  e,  arciform  fibres;  /,  fibres  described 
by  Solly  as  passing  from  the  anterior  column  of  the  cord  to  the  cerebellum;  g,  anterior  column  of 
the  spinal  cord;  /i,  lateral  column;  p,  pons  Varolii;  i,  its  upper  fibres;  5,  5,  roots  of  the  fifth  pair  of 
nerves. 

Fig.  322.— Posterior  surface  of  the  pons  Varolii,  corpora  quadrigemina,  and  medulla  oblongata. 
The  peduncles  of  the  cerebellum  are  cut  short  at  the  side,  a,  a,  the  upper  pair  of  corpora  quadri- 
gemina; 6,  6,  the  lower;  /,  /,  superior  peduncles  of  the  cerebellum;  c,  eminence  connected  with  the 
nucleus  of  the  hypoglossal  nerve;  e,  that  of  the  glosso-pharyngeal  nerve;  that  of  the  vagus  nerve; 
d,  d,  restiform  bodies;  p,  p,  posterior  pyramids;  v,  v,  groove  in  the  middle  of  the  fourth  ventricle, 
ending  below  in  the  calamus  scriptorius ;  7,  7,  roots  of  the  auditory  nerves. 

Structure. — The  grey  substance  which  it  contains  is  situated  in  the 
interior,  and  variously  divided  into  masses  and  laminae  by  the  white  or 
fibrous  substance  which  is  arranged  partly  in  external  columns,  and  partly 
in  fasciculi  traversing  the  central  grey  matter.  The  medulla  oblongata 
is  larger  than  any  part  of  the  spinal  cord.  Its  columns  are  pyrif  orm, 
enlarging  as  they  proceed  toward  the  brain,  and  are  continuous  with  those 


106  HAT^[D-BOOK  OF  PHYSIOLOGY.  ^ 

of  the  spinal  cOrd.  Each  half  of  the  medulla,  therefore,  may  be  divided 
into  three  columns  or  tracts  of  fibres,  continuous  with  the  three  tracts  of 
which  each  half  of  the  spinal  cord  is  made  up.  The  columns  are  more 
prominent  than  those  of  the  spinal  cord,  and  separated  from  each  other 
by  deeper  grooves.  The  anterior,  continuous  with  the  anterior  columns 
of  the  cord,  are  called  the  mitQYioY  pyramids;  the  jjosterior,  continuous 
with  the  posterior  columns  of  the  cord,  and  comprising  the  funiculus  ctme- 
atus,  and  the  funiculus  of  Kolando  (Fig.  323,  f.c,  f.B.),  are  called  the 
restiform  bodies.  On  the  otiter  side  of  the  anterior  pyramids  of  each 
side,  near  its  upper  part,  is  a  small  oval  mass  containing  grey  matter, 
and  named  the  olivarij  tody;  and  at  the  posterior  part  of  the  restiform 
column,  immediately  on  each  side  of  the  posterior  median  groove,  con- 
tinuotis  with  the  posterior  median  column  of  the  cord,  a  small  tract  is 
marked  otf  by  a  slight  groove  from  the  remainder  of  the  restiform  body, 
and  eddied  the  posterior  pyra/)iid  or  fasciciclus  gracilis.  The  restiform 
columns,  instead  of  remaining  parallel  with  each  other  throughout  the 
whole  length  of  the  medtilla  oblongata,  diverge  near  its  upper  part,  and 
by  thtis  diverging,  lay  open,  so  to  speak,  -a  space  called  the  f otirth  ven- 
tricle, the  floor  of  which  is  formed  by  the  grey  matter  of  the  interior  of 
the  medtilla,  by  this  divergence  exposed. 

On  separating  the  anterior  pyramids,  and  looking  into  the  groove 
between  them,  some  decussating  fibres  of  the  lateral  columns  of  the  cord 
can  be  plainly  seen. 


DlSTEIBUTIOK  OF  THE  FlBRES  OF  THE  MeDULLA  OBLONGATA. 

The  anterior  pyramid  of  each  side,  although  mainly  composed  of  con- 
tinuations of  the  fibres  of  the  anterior  columns  of  the  spinal  cord,  receives 
fibres  from  the  lateral  columns,  both  of  its  own  and  the  opposite  side;  the 
latter  fibres  forming  almost  entirely  the  decussating  strands  whicli  are 
seen  in  the  groove  between  the  anterior  pyramids.  Thus  composed,  the 
anterior  pyramidal  fibres  proceeding  onward  to  the  brain  are  distributed 
in  the  following  manner: — 

1.  The  greater  part  pass  on  through  the  Pons  to  the  Cerebrum.  A 
portion  of  the  fibres,  however,  running  apart  from  the  others,  joins  some 
fibres  from  the  olivary  body,  and  unites  with  them  to  form  what  is  called 
the  olivary  fasciculus  or  fillet.  2.  A  small  tract  of  fibres  proceeds  to  the 
cerebellum. 

The  lateral  colum)i  of  the  cord  on  each  side  of  tlie  medulla,  in  pro- 
ceeding upward,  divides  into  three  jiarts,  outer,  inner,  and  middle,  which 
are  thus  disposed  of: — 1.  The  outer  fibres  (direct  cerebellar  tract)  go' with 
the  restiform  tract  to  the  cerebellum.  2.  The  middle  (crossed  pyramidal 
tract)  decussate  across  the  middle  line  with  their  fellows,  and  form  a  part 
of  the  anterior  pyramid  of  the  opi)osite  side.  3.  The  i)uier  pass  on  to 
the  cerebrum,  at  first  superficially  but  afterward  beneath  the  olivary  body 
and  the  arcuate  fibres,  and  then  proceed  along  the  floor  of  the  fourth 
ventricle,  on  each  side,  under  the  name  of  the  fasciculus  teres. 


THE  NERVOUS  SYSTEM. 


107 


The  posterior  column  of  the  cord  is  represented  in  the  medulla  by  the 
posterioi'  pyramid,  or  fasciculus  gracilis,  which  is  a  continuation  of  the 
posterior  median  column,  and  by  the  restiform  body,  comprising  the 
funiculus  cuneatus  and  the  funiculus  of  Rolando.  The  fasciculus  gracilis 
(Fig.  323,  f.g)y  diverges  above  as  the  broader  clava  to  form,  one  on  either 
side,  the  lower  lateral  boundary  of  the  fourth  ventricle,  then  tapers  off, 
and  becomes  no  longer  traceable.  The  funiculus  cuneatus,  or  the  rest  of 
the  posterior  column  of  the  cord,  is  continued  up  in  the  medulla  as  such 
(Fig.  323,  /.  c) ;  but  soon,  in  addition,  between  this  and  the  continuation 
of  the  posterior  nerve  roots,  appears  another  tract  called  the  funiculus  of 
Kolando  (Fig.  323, /.J?).    High  up,  the  funiculus  cuneatus  is  covered 


Fig.  323.— Posterior  view  of  the  medulla,  fourth  ventricle,  and  mesencephalon  (natural  size). 
p.  w,  line  of  the  posterior  roots  of  the  spinal  nerves;  p.m.f.,  posterior  median  fissure;  /.g.,  funiculus 
gracilis;  cl.,  its  clavis;  /.c,  funiculus  cuneatus;  /.i?.,  funiculus  of  Rolando;  r.6.,  restiform  body; 
C.S.,  calamus  scriptorius;  I.,  section  of  hgula  or  taenia;  part  of  choroid  plexus  is  seen  beneath  it;  l.r., 
lateral  recess  of  the  ventricle;  str.,  striae  acusticae;  z./.,  inferior  fossa;  s./.,  posterior  fossa;  between 
It  and  the  median  sulcus  is  the  fasciculus  teres;  c&Z.,  cut  surface  ^f  the  cerebellar  hemisphere;  n.d., 
central  or  grey  matter;  s.m.v.,  superior  medullary  velum;  Ingf,  Ugula;  s.c.p.,  superior  cerebellar 
peduncle  cut  longitudinally;  cr.,  combined  section  of  the  three  cerebellar  peduncles;  c.g.s.,  c.q.i.,  cor- 
pora quadrigemina  (superior  and  inferior);  /r.,  fraenulum;  /.,  fibres  of  the  fillet  seen  on  the  surface 
of  the  tegmentum;  c,  crusti;  Z.gr.,  lateral  groove;  c.g.i.,  corpus  geniculum  internus;  i/i.,  posterior 
part  of  thalamus;  _p.,  pineal  body.  The  roman  numbers  indicate  the  corresponding  cranial  nerves. 
(E.  A.  Schafer.) 


by  a  set  of  fibres  (arcuate  fibres),  which  issue  from  the  anterior  median 
fissure,  turn  upward  over  the  anterior  pyramids  to  pass  directly  into  the 
corresponding  hemisphere  of  the  cerebellum,  being  joined  by  the  fibres  of 
the  direct  cerebellar  tract;  the  funiculus  of  Rolando,  and  the  funiculus 
cuneatus,  although  appearing  to  join  them,  do  not  actually  do  so,  except 
to  a  partial  extent. 


Grey  matter  of  tlie  medulla. — To  a  considerable  extent  the.  grey  matter 


108 


HAND-BOOK  OF  PHYSIOLOGY. 


of  the  medulla  is  a  continuation  of  that  in  the  spinal  cord,  but  the  ar- 
rangement is  somewhat  different. 

The  displacement  of  the  anterior  cornu  takes  place  because  of  the 
decussation  of  a  large  part  of  the  fibres  of  the  lateral  columns  in  the 
anterior  pyramids  passing  through  the  grey  matter  of  the  anterior  cornu, 
so  tliat  the  caput  cornu  is  cut  off  from  the  rest  of  the  grey  matter,  and  is, 
moreover,  pushed  backward  by  the  olivary  body,  to  be  mentioned  below. 
It  lies  in  the  lateral  portion  of  the  medulla,  and  exists  for  a  time  as  the 
nucleus  lateralis  (Fig.  324,  n.l)',  it  consists  of  a  reticulum  of  grey  matter, 
containing  ganglion  cells  intersected  by  white  nerve  fibres.  The  base  of 
the  anterior  cornu  is  pushed  more  from  the  anterior  surface,  and  when 


Fig.  324.— Section  of  the  mediilla  oblongata  in  the  region  of  the  superior  pyramidal  decussation. 
a.m.f.,  anterior  median  fissure:  /.«..  superficial  arciform  fibres  emerging  from  the  fissure:  py.. 
pyramid;  n. a. r., nuclei  of  arciform  fibres:  /.ai.  deep  arciform  becoming  supei-ficial:  o.,  lower  end  of 
olivary  nucleus;  n.l.,  nucleus  lateralis:  /.r.,  formatio  reticularis:  /.a-,  arciform  fibres  proceeding 
from  the  formatio  reticularis;  (/.,  substantia  gelatinosa  of  Rolando:  a.F.,  ascending  root  of  fifth 
nerve:  w.c,  nucleus  cuneatus;  n.c'.,  external  cuneate  nucleus;  7i.gf.,  nucleus  gi'acilis: /.p.,  nucleus 
gracilis;  p.m.f.,  posterior  median  fissure ;  c.c,  central  canal  surrounded  'by  grej'  matter,  in  which 
are  n.XI.,  nucleus  of  the  spinal  accessory,  and  n.XII.,  nucleus  of  the  hypoglossal;  s.rf.,  superior 
pyramidal  decussation.   (Schwalbe.)   (Modified  from  Quain.) 

the  central  canal  opens  out  into  the  fourth  ventricle,  forms  a  collection  of 
ganglion  cells,  producing  the  eminence  of  the  fasciculus  teres;  from  cer- 
tain large  cells  in  it  arise  the  hypoglossal  nerve  (Fig.  325,  XI I.),  which 
l)asses  through  the  medulla,  and  appears  between  the  olivary  body  and 
the  anterior  pyramids. 

In  the  funiculus  teres,  nearer  to  the  middle  line  as  well  as  to  the  sur- 
face, is  a  collection  of  nerve  cells  called  the  nucleus  of  that  funiculus  (Fig. 
325,  n.t).  1'lie  grey  matter  of  the  posterior  cornu  is  dis})laced  somewhat 
by  bands  of  fibres  jiassing  through  it.  The  caput  cornu  appears  at  the 
surface  as  the  funiculus  of  Kolando,  wliilst  the  cervix  cornu  is  broken  up 
into  a  reticulated  structure  which  is  displaced  laterally,  similar  in  struc- 
ture to  the  nucleus  lateralis.  From  the  increase  of  the  base  of  the  posterior 
cornu,  the  nuclei  of  the  funiculus  gracilis  and  funiculus  cuneatus  are  de- 


THE  NERVOUS  SYSTEM. 


109 


rived  (Fig.  324,  n.g,  n.c),  and  outside  of  the  latter  is  an  accessory  nucleus 
formed  (Fig.  324,  n.c').  Internally  to  these  latter,  and  also  derived  from 
the  cells  of  the  base  of  the  posterior  cornu  and  appearing  in  the  floor  of 
the  fourth  ventricle,  when  the  central  canal  opens  are  the  nuclei  of  the 
spinal  accessory,  vagus,  and  glosso-pharyngeal  nerves.  In  the  upper  part 
of  the  medulla  also,  to  the  outside  of  these  three  nuclei,  is  found  the 

Erincipal  auditory  nucleus.  All  the  above  nuclei  appear  to  be  derived 
:om  a  continuation  of  the  grey  matter  of  the  spinal  cord,  but  a  fresh  col- 


FiG.  325.— Section  of  the  medulla  oblongata  at  about  the  middle  of  the  olivary  body,  f.l.a.., 
anterior  median  fissure ;  n.a.r.,  nucleus  arciformis;  p,  pyi-amid;  XiZ,  bundle  of  hypoglossal  nerve 
emerging  from  the  surface :  at  b,  it  is  seen  coursing  between  the  pyramid  and  the  ohvary  nucleus, 
0.;  f.a.e.,  external  arciform  fibres;  n.l.,  nucleus  lateralis;  a,  arciform  fibres  passing  toward  resti- 
form  body,  partly  through  the  substantia  gelatinosa,  g.,  partly  superficial  to  the  ascending  root  of 
the  fifth  nerve,  a.V.;  X,  bundle  of  vagus  root  emerging;  /.r.,  formatio  reticularis;  c.r.,  corpus  resti- 
forme,  beginning  to  be  formed,  chiefly  by  arciform  fibres,  superficial  and  deep;  n.c  nucleus  cunea- 
tus;  n.g.,  nucleus  gracilis;  f.,  attachment  of  the  ligula;  /.s.,  funiculus  solitarius;  n.X.,  7iX'.,  two 
parts  of  the  vagus  nucleus ;  n.XIL,  hypoglossal  nucleus;  n.t.,  nucleus  of  the  funiculus  teres;  n.am., 
nucleus  ambiguous;  r.,  raphe;  ^4..  continuation  of  the  anterior  column  of  cord;  o',  o".,  accessory 
olivary  nucleus;  p.o.,  pedimculus  oUvse.   (Schwalbe.)  (.Modified  from  Quain.) 

lection  of  grey  matter  not  represented  is  interpolated  between  the  anterior 
pyramids  and  the  lateral  column,  contained  within  the  olivary  promi- 
nence, the  wavy  line  of  which  (corpus  dentatum)  is  doubled  upon  itself 
at  an  angle  with  the  extremities  directed  upward  and  inward  (Fig.  325,  o). 
There  may  also  be  a  smaller  collection  of  grey  matter  on  the  outer  and 
inner  side  of  the  olivary  nucleus  known  as  accessory  olivary  nuclei. 

FUKCTIOKS  OP  THE  MeDULLA  OBLONGATA. 

The  functions  of  the  medulla  oblongata,  like  those  of  the  spinal  cord, 
may  be  considered  under  the  heads  of:  1.  Conduction;  2.  Transference 
and  Reflection;  and,  in  addition,  3.  Automatism. 

1.  In  conducting  impressions  the  medulla  oblongata  has  a  wider  ex- 
tent of  function  than  any  other  part  of  the  nervous  system,  since  it  is 


110 


HAND-BOOK  OF  PHYSIOLOGY. 


obvious  that  all  impressions  passing  to  and  fro  between  the  brain  and  the 
spinal  cord  and  all  nerves  arising  below  the  pons,  must  be  transmitted 
through  it. 

2.  As  a  nerve-centre  by  which  impressions  are  transferred  or  reflected, 
the  medulla  oblongata  also  resembles  the  spinal  cord;  the  only  difference 
between  them  consisting  of  the  fact  that  many  of  the  reflex  actions  per- 
formed by  the  former  are  much  more  important  to  life  than  any  per- 
formed by  the  spinal  cord. 

Demonstration  of  Functions. — It  has  been  proved  by  repeated 
experiments  on  the  lower  animals  that  the  entire  brain  may  be  gradually 
cut  away  in  successive  portions,  and  yet  life  may  continue  for  a  consider- 
able time,  and  the  respiratory  movements  be  uninterrupted.  Life  may 
also  continue  when  the  spinal  cord  is  cut  away  in  successive  portions  from 
below  upward  as  high  as  the  point  of  origin  of  the  phrenic  nerve.  In 
Amphibia,  the  brain  has  been  all  removed  from  above,  and  the  cord,  as 
far  as  the  medulla  oblongata,  from  below;  and  so  long  as  the  medulla 
oblongata  was  intact,  respiration  and  life  were  maintained.  But  if,  in 
any  animal,  the  medulla  oblongata  is  wounded,  particularly  if  it  is 
wounded  in  its  central  part,  opposite  the  origin  of  the  pneumogastric 
nerves,  the  respiratory  movements  cease,  and  the  animal  dies  asphyxi- 
ated. And  this  efPect  ensues  even  when  all  parts  of  the  nervous  system, 
except  the  medulla  oblongata,  are  left  intact.  I 

Injury  and  disease  in  men  prove  the  same  as  these  experiments  on  | 
animals.    Numerous  instances  are  recorded  in  which  injury  to  the  me-  I 
dulla  oblongata  has  produced  instantaneous  death;  and,  indeed,  it  is  ' 
through  injury  of  it,  or  of  the  part  of  the  cord  connecting  it  with  the 
origin  of  the  phrenic  nerve,  that  death  is  commonly  produced  in  fractures 
and  diseases  with  sudden  displacement  of  the  upper  cervical  vertebrae. 

Special  Centkes. 

(1.)  Respiratory, — The  centre  whence  the  nervous  force  for  the  pro- 
duction of  combined  respiratory  movements  appears  to  issue  is  in  the  in- 
terior of  that  part  of  the  medulla  oblongata  from  which  the  pneumo- 
gastric nerves  or  Vagi  arise.  The  vagi  themselves,  indeed,  are  not  essen- 
tial to  the  respiratory  movements;  for  both  may  be  divided  without  more 
immediate  effect  than  a  retardation  of  these  movements.  But  in  this 
part  of  the  medulla  oblongata  is  the  nerve-centre  whence  the  impulses 
producing  the  respiratory  movements  issue,  and  through  which  impulses 
conveyed  from  distant  parts  are  reflected. 

The  wide  extent  of  connection  which  belongs  to  tlie  medulla  oblongata 
as  the  centre  of  the  respiratory  movements,  is  shown  by  the  fact  that 
impressions  by  mechanical  and  other  ordinary  stimuli,  made  on  many 
parts  of  tlie  external  or  internal  surface  of  tlie  body,  may  modify,  i.e.,  in- 


THE  NERVOUS  SYSTEM. 


Ill 


crease  or  diminish  the  rapidity  of  respiratory  movements.  Thus  involun- 
tary respirations  are  induced  by  the  sudden  contact  of  cold  with  any  part 
of  the  skin,  as  in  dashing  cold  water  on  the  face.  Irritation  of  the 
mucous  membrane  of  the  nose  produces  sneezing.  Irritation  in  the 
pharynx,  oesophagus,  stomach,  or  intestines,  excites  the  concurrence  of  the 
respiratory  movements  to  produce  vomiting.  Violent  irritation  in  the 
rectum,  bladder,  or  uterus,  gives  rise  to  a  concurrent  action  of  the 
respiratory  muscles,  so  as  to  effect  the  expulsion  of  the  faeces,  urine,  or 
fcetus. 

(2.)  Centre  for  Deglutition. — The  medulla  oblongata  appears  to  be 
the  centre  whence  are  derived  the  motor  impulses  enabling  the  muscles 
of  the  palate,  pharynx,  and  oesophagus  to  produce  the  successive  co-ordi- 
nate and  adapted  movements  necessary  to  the  act  of  deglutition  (p.  239, 
Vol.  I.).  This  is  proved  by  the  persistence  of  swallowing  in  some  of  the 
lower  animals  after  destruction  of  the  cerebral  hemispheres  and  cere- 
bellum; its  existence  in  anencephalous  monsters;  the  power  of  swallowing 
possessed  by  the  marsupial  embryo  before  the  brain  is  developed;  and  by 
the  complete  arrest  of  the  power  of  swallowing  when  the  medulla  ob- 
longata is  injured  in  experiments.  (3)  A  centre  by  which  the  move- 
ments of  mastication  are  regulated  (p.  226,  Vol.  I.).  (4)  Through  the 
medulla  oblongata,  chiefly,  are  reflected  the  impressions  which  excite  the 
secretion  of  saliva  (p.  232,  Vol.  I.).  (5)  Cardio-inhiMtory  centre  for  the 
regulation  of  the  action  of  the  heart,  through  the  pneumogastrics  and 
probably  also,  the  accelerating  fibres  of  the  sympathetic  (p.  127,  Vol.  I.). 
(6)  The  chief  vaso-motor  centre.  From  this  centre  arise  fibres  which, 
passing  down  the  spinal  cord,  issue  with  the  anterior  roots  of  the  spinal 
nerves,  and  enter  the  ganglia  and  branches  of  the  sympathetic  system,  by 
which  they  are  conducted  to  the  blood-vessels  (p.  154,  Vol.  I.).  (7)  Gilio- 
spinal  centre  for  the  regulation  of  the  iris,  and  other  plain-fibred  muscles 
of  the  eye.  (8  and  9)  Centres  or  ganglia  of  the  special  senses  of  hearing 
and  taste.  (10)  The  centre  for  speech,  i.e.,  the  centre  by  which  the 
various  muscular  movements  concerned  in  speech  are  co-ordinated  or  har- 
monized. (11)  Centre  by  which  the  many  muscles  concerned  in  vomiting 
are  harmonized.  (12)  The  so-called  diahetic  centre,  or,  in  other  words, 
the  grey  matter  in  the  medulla  oblongata  which,  being  irritated,  causes 
glycosuria  (p.  283,  Vol.  I.),  is  probably  the  vaso-motor  centre;  and  this 
peculiar  result  of  its  stimulation  is  merely  due  to  vaso-motor  changes  in 
the  liver. 

Though  respiration  and  life  continue  while  the  medulla  oblongata  is 
perfect  and  in  connection  with  the  respiratory  nerves,  yet,  when  all  the 
brain  above  it  is  removed,  there  is  no  more  appearance  of  sensation,  or 
will,  or  of  any  mental  act  in  the  animal,  the  subject  of  the  experiment, 
than  there  is  when  only  the  spinal  cord  is  left.  The  movements  are  all 
involuntary  and  unfelt;  and  the  medulla  oblongata  has,  therefore,  no 


112 


HAND-BOOK  OF  PHYSIOLOGY. 


claim  to  be  considered  as  an  organ  of  the  mind,  or  as  the  seat  of  sensation 
or  voluntary  power.  These  are  connected  with  parts  to  be  afterward 
described. 


Structure. — The  meso-cephalon,  or  pons  Varolii,  (yi,  Fig.  326),  is 
composed  principally  of  transverse  fibres  connecting  the  two  hemispheres 
of  the  cerebellum,  and  forming  its  principal  transverse  commissure.  But 
it  includes,  interlacing  with  these,  numerous  longitudinal  fibres  which 
connect  the  medulla  oblongata  with  the  cerebrum,  and  transverse  fibres 
which  connect  it  with  the  cerebellum.    Among  the  fasciculi  of  nerve- 


FiG.  326.— Base  of  the  brain.  1,  superior  longitudinal  fissure;  2,  2',  2",  anterior  cerebral  lobe;  3, 
fissvu-e  of  Sylvius,  between  anterior  and  4,4',4",  middle  cerebral  lobe;  5,  5',  posterior  lobe;  6,  medulla 
oblongata;  the  figure  is  in  the  right  anterior  pyramid:  7,8,9,10,  the  cerebellum;  +,  the  inferior  ver- 
miform process.  The  figures  from  I.  to  IX.  are  placed  against  the  corresponding  cerebral  nerves; 
ni.  is  placed  on  the  right  crus  cerebri.  VI.  and  VII.  on  the  pons  Varolii;  X.  the  first  cervical  or  sub- 
occipital nerve.   (Allen  Thomson).  J^. 

fibres  by  which  these  several  parts  are  connected,  the  pons  also  contains 
abundant  grey  or  vesicular  substance,  which  appears  irregularly  placed 
among  the  fibres,  and  fills  up  all  the  interstices. 

Functions. — The  anatomical  distribution  of  the  fibres,  both  trans- 
verse and  longitudinal,  of  which  the  pons  is  composed,  is  sufficient  evi- 
dence of  its  fun3tions  as  a  conductor  of  impressions  from  one  part  of  the 
ccrebro-spinal  axis  to  anotlier.  Concerning  its  functions  as  a  nerve- 
centre,  little  or  nothing  is  certainly  known. 


PoKS  Varolii. 


THE  NERVOUS  SYSTEM. 


113 


Crura  Cerebri. 

Structure. — The  crura  cerebri  (iii,  Fig.  326),  are  principally  formed 
of  nerve-fibres,  of  which  the  inferior  or  more  superficial  (crusta)  are  con- 
tinuous with  those  of  the  anterior  pyramidal  tracts  of  the  medulla  oblon- 
gata, and  the  superior  or  deeper  fibres  (tegmentum)  with  the  lateral  and 
posterior  pyramidal  tracts,  and  with  the  olivary  fasciculus.  Besides  these 
fibres  from  the  medulla  oblongata,  are  others  from  the  cerebellum;  and 


Fig.  327.— Dissection  of  brain,  from  above,  exposing  the  lateral  fourth  and  fifth  ventricles  with 
the  surrounding  parts.  a,  anterior  part,  or  genu  of  corpus  callosum;  6,  corpus  striatum;  6',  the 
corpus  striatum  of  left  side,  dissected  so  as  to  expose  its  grey  substance ;  c,  points  by  a  line  to  the 
taenia  semicircularis ;  d,  optic  thalamus;  e,  anterior  pillars  of  fornix  divided;  below  they  are  seen 
descending  in  front  of  the  third  ventricle,  and  between  them  is  seen  part  of  the  anterior  commissure; 
in  front  of  the  letter  e  is  seen  the  slit-like  fifth  ventricle,  between  the  two  laminae  of  the  septum  luci- 
dum;  /,  soft  or  middle  commissure;  gr,  is  placed  in  the  posterior  part  of  the  third  ventricle;  immedi- 
ately behind  the  latter  are  the  posterior  commissure  (just  visible)  and  the  pineal  gland,  the  two  crura 
of  which  extend  forward  along  the  inner  and  upper  margins  of  the  optic  thalami ;  h  and  the  cor- 
pora quadrigemina;  fc,  superior  crus  of  cerebellum;  close  to  fc  is  the  valve  of  Vieussens,  which  has- 
been  divided  so  as  to  expose  the  fourth  ventricle;  hippocampus  major  and  corpus  flmbriatum,  or 
taenia  hippocampi;  hippocampus  minor;  eminentia  collateralis;  o,  fourth  ventricle;  p,  posterior 
surface  of  meduUa  oblongata;  r,  section  of  cerebellxun;  s,  upper  part  of  left  hemisphere  of  cerebel- 
lum exposed  by  the  removal  of  part  of  the  posterior  cerebral  lobe.   (Hirschfeld  and  Leveille.) 

some  of  the  latter  as  well  as  a  part  of  the  fibres  derived  from  the  lateral 
tract  of  the  medulla  oblongata,  decussate  across  the  middle  line. 

Each  crus  cerebri  contains  among  its  fibres  a  mass  of  grey  substance, 
the  locus  niger. 

Functions. — With  regard  to  their  functions,  the  crura  cerebri  may 
be  regarded  as,  principally,  conducting  organs:   the  crusta  conducting 
Vol.  II.— 8 


114 


HAND-BOOK  OF  PHYSIOLOGY. 


motor  and  the  tegmentum  sensory  impressions.  As  nerve-centres  they 
are  probably  connected  with  the  functions  of  the  tliird  cerebral  nerve, 
which  arises  from  the  locus  niger,  and  through  which  are  directed  the 
chief  of  the  numerous  and  complicated  movements  of  the  eyeball.  The 
crura  cerebri  are  also  in  all  probability  connected  with  the  co-ordination 
of  other  movements  besides  those  of  the  eye,  as  either  rotatory  (p.  119, 
Vol.  II.)  or  disorderly  movements  result  after  section  of  either  of  them. 

COKPORA  QUADRIGEMIKA. 

The  corpora  quadrigemina  (from  which,  in  function,  the  corpora  gen- 
iculata  are  not  distinguishable),  are  the  homologues  of  the  optic  lobes  in 
Birds,  Amphibia,  and  Fishes,  and  may  be  regarded  as  the  principal 
nerve-centres  for  the  sense  of  sight. 

Functions. — (1)  The  experiments  of  Flourens,  Longet,  and  Hert- 
wig,  show  that  removal  of  the  corpora  quadrigemina  wholly  destroys  the 
power  of  seeing;  and  diseases  in  which  they  are  disorganized  are  usually 
accompanied  by  blindness.  Atrophy  of  them  is  also  often  a  consequence 
of  atrophy  of  the  eyes.  Destruction  of  one  of  the  corpora  quadrigemina 
(or  of  one  optic  lobe  in  birds),  produces  blindness  of  the  opposite  eye. 
This  loss  of  sight  is  the  only  apparent  injury  of  sensibility  sustained  by 
the  removal  of  the  corpora  quadrigemina.  The  (2)  removal  of  one  of  them 
affects  the  movements  of  the  body,  so  that  animals  rotate,  as  after 
division  of  the  crus  cerebri,  only  more  slowly:  but  this  may  be  due  to 
giddiness  and  partial  loss  of  sight.  (3)  The  more  evident  and  direct  in- 
fluence is  that  produced  on  the  iris.  It  contracts  when  the  corpora  quad- 
rigemina are  irritated:  it  is  always  dilated  when  they  are  removed:  so 
that  they  may  be  regarded,  in  some  measure  at  least,  as  the  nervous 
centres  governing  its  movements,  and  adapting  them  to  the  impressions 
derived  from  the  retina  through  the  optic  nerves  and  tracts.  (4)  The 
centre  for  the  co-ordination  of  the  movements  of  the  eyes  is  also  contained 
in  them.  This  centre  is  closely  associated  with  that  for  contraction  of 
the  ]Dupil,  and  so  it  follows  that  contraction  or  dilatation  follows  upon 
certain  definite  ocular  movements. 

Corpora  Striata  and  Optic  Thalami. 

Structure. — (1.)  The  corpora  striata  are  situated  in  front  of  the  optic 
thalami,  partly  within  and  partly  without  the  lateral  ventricle.  Each 
corpus  striatum  consists  of  two  parts. 

(«.)  Intraventricular  portion  {caudate  nucleus)  is  conical  in  shape, 
with  the  base  of  the  cone  forward;  it  consists  of  grey  matter,  with  wliite 
substance  in  its  centre,  which  comes  from  tlie  corresponding  cerebral 
peduncle,    (b.)  Extraventricular  portion  (lenticular  nucleus)  is  separated 


THE  NERVOUS  SYSTEM. 


115 


from  tlie  other  portion  by  a  layer  of  white  material.  It  is  seen  on  section 
of  the  hemisphere.  Its  horizontal  section  is  wider  in  the  centre  than  at 
the  end.    On  the  outside  is  the  grey  lamina  {claustrum). 

Between  the  corpus  striatum  and  optic  thalamus  is  the  tcenia  semicir- 
cular is,  a  semi-transparent  band  which  is  continued  back  into  the  white 
substance  of  the  roof  of  the  descending  horn  of  the  ventricle. 

(2)  The  Optic  Thalami  are  oval  in  shape,  and  rest  upon  the  crura 
cerebri.  The  upper  surface  of  each  thalamus  is  free,  and  of  white  sub- 
stance; it  projects  into  the  lateral  ventricle.  The  posterior  surface  is  also 
white.  The  inner  sides  of  the  two  optic  thalami  are  in  partial  contact, 
and  are  composed  of  grey  material  uncovered  by  white,  and  are,  as  a  rule, 
connected  by  a  transverse  portion. 

Functions. — The  two  ganglia,  the  Corpus  Striatum  and  Optic  Thal- 
amus, are  placed  between  the  cerebral  convolutions  and  the  crus  cerebri 
of  the  same  side.  It  is  probable  that  although  some  of  the  fibres  of  the 
crus  pass  without  interruption  into  the  cerebrum,  the  majority  of  the 
fibres  pass  into  these  ganglia;  first  of  all  the  lower  fibres  (crusta)  into  the 
corpus  striatum,  and  the  upper  (tegmentum)  into  the  optic  thalamus,  and 
then  out  into  the  cerebrum.  From  the  position  of  these  bodies,  it  would 
be  reasonable  to  suppose  that  they  were  interposed  in  function  between 
the  operation  of  the  will  on  the  one  hand,  and  on  the  other  with  the  sen- 
sori-motor  apparatus  below  them,  and  it  is  believed  that  this  is  the  case, 
although  the  evidence  is  not  exact:  the  theory  that  the  corpus  striatum 
is  the  motpr  ganglion,  and  that,  when  injured,  the  communication  be- 
tween the  will  and  the  muscles  of  one  half  of  the  body  is  broken  (hemi- 
plegia), being  supported  by  many  pathological  facts  and  physiological  ex- 
periments, and  generally  received  by  pathologists.  It  is  found  that  the 
cerebral  functions  are  as  a  rule  unimpaired.  In  the  same  way  the  evidence 
that  the  optic  thalamus  is  the  sensory  ganglion  depends  upon  similar 
observations,  that  when  injured  or  destroyed,  sensation  of  the  opposite 
side  of  the  body  is  impaired  or  lost.  In  both  cases,  the  parts  paralyzed 
are  on  the  opposite  side  to  the  lesions,  the  decussation  of  both  sets  of 
fibres  taking  place,  as  we  have  seen,  below  the  ganglia.  It  is  a  fact, 
however,  that  many  experiments  and  pathological  observations  are  op- 
posed to  the  above  theory,  which  must  therefore  be  received  with  caution. 

The  Cerebellum. 

The  Cerebellum  (7,  8,  9,  10,  Fig.  326),  is  composed  of  an  elongated 
central  portion  called  the  vermiform  processes,  and  two  hemispheres. 
Each  hemisphere  is  connected  with  its  fellow,  not  only  by  means  of  the 
vermiform  processes,  but  also  by  a  bundle  of  fibres  called  the  middle  crus 
OT  peduncle  (the  latter  forming  the  greater  part  of  the  pons  Varolii),  while 
the  superior  crura  with  the  valve  of  Vieussens  connect  it  with  the  cere- 


116 


HAND-BOOK  OF  PHYSIOLOGY. 


brum  (5,  Fig.  328),  and  the  inferior  crura  (formed  by  the  prolonged  res- 
tiform  bodies)  connect  it  with  the  medulla  oblongata  (3,  Fig.  328). 

Structure. — The  cerebellum  is  composed  of  white  and  grey  matter, 
the  latter  being  external,  like  that  of  the  cerebrum,  and  like  it,  infolded. 


Fig.  328. — Cerebellum  in  section  and  of  fourth  ventricle,  with  the  neighboring  parts.  1,  median 
groove  of  fourth  ventricle,  ending  below  in  the  calamus  scriptorius,  with  the  longitudinal  eminences 
formed  by  the  fasciculi  teretes,  one  on  each  side ;  2,  the  same  groove,  at  the  place  where  the  white 
streaks  of  the  auditory  nerve  emerge  from  it  to  cross  the  floor  of  the  ventricle ;  3,  inferior  crus  or 
peduncle  of  the  cerebellum,  formed  by  the  restiform  body;  4,  posterior  pyramid;  above  this  is  the 
calamus  scriptorius;  5,  superior  crus  of  cerebellum,  or  processus  e  cerebello  ad  cerebrum  (or  ad 
testes);  6,  6,  fillet  to  the  side  of  the  crura  cerebri;  7,  7,  lateral  grooves  of  the  crura  cerebri;  8,  cor- 
pora quadrigemina.   (From  Sappey  after  Hirschfeld  and  Leveille.) 

SO  that  a  larger  area  may  be  contained  in  a  given  space.  The  convolutions 
of  the  grey  matter,  however,  are  arranged  after  a  different  pattern,  as 
shown  in  Fig.  328.  Besides  the  grey  substance  on  the  surface,  there  is, 
near  the  centre  of  the  white  substance  of  each  hemisphere,  a  small  capsule 


Fig.  329.— Outline  sketch  of  a  section  of  the  cerebellum,  showing  the  corpus  dentatum.  The 
section  has  been  carried  through  the  left  lateral  part  of  the  pons,  so  as  to  divide  the  superior  pedun- 
cle and  pass  nearly  through  the  middle  of  the  left  cerebellar  hemisphere.  The  olivary  body  has 
also  been  divided  longitudinally  so  as  to  expose  in  section  its  corpus  dentatuDi.  c  r,  crus  cerebri;  /, 
fillet;  corpora  (luadrigeminii;  .s- p,  superior  peduncle  of  the  cerebellunulivided;  m  middle  pedun- 
cle or  lateral  part  of  the  pons  Varolii,  with  tibics  i);issing  Ironi  i(  into  the  white  stem;  a  i\  continu- 
ation of  the  white  steni  radiating  toward  the  arbor  vita;  of  t  he  folia;  c;  (/,  corpus  dentatum;  o, 
olivary  body  with  its  corpus  dentatum;     anterior  pyramid.   (Allen  Thomson.)  %. 

of  grey  matter  called  the  corpus  dentatum  (Fig.  329,  ^-^7)  resembling  very 
closely  the  corpus  dentatum  of  the  olivary  body  of  the  medulla  oblongata 
(Fig.  324,  0). 


THE  NERVOUS  SYSTEM. 


117 


If  a  section  be  taken  throngli  the  cortical  portion  of  the  cerebellum, 
the  following  distinct  layers  can  be  seen  (Fig.  330)  by  microscopic  exami- 
nation. 

(1.)  Immediately  beneath  the  pia  mater  {p  7v)  is  a  layer  of  consider- 
able thickness,  which  consists  of  a  delicate  connective  tissue,  in  which  are 


Fig.  330.— Vertical  section  of  dog's  cerebellum;  p  m,  pia  mater;  p,  corpuscles  of  Purkinje,  which 
are  branched  nerve-cells  lying  in  a  single  layer  and  sending  single  processes  downward  and  more 
numerous  ones  upward,  which  branch  continuously  and  extend  through  the  deep  "molecular  layer" 
toward  the  free  surface ;  g,  dense  layer  of  ganglionic  corpuscles,  closely  resembling  nuclear  layers 
of  retina;  /,  layer  of  nerve-fibres,  with  a  few  scattered  ganglionic  corpuscles.  This  last  layer  iff) 
constitutes  part  of  the  white  matter  of  the  cerebellum,  while  the  layers  between  it  and  the  free  sur- 
face are  grey  matter.   (Klein  and  Noble  Smith.) 

scattered  several  spherical  corpuscles  like  those  of  the  granular  layer  of  the 
retina,  and  also  an  immense  number  of  delicate  fibres  passing  up  toward 
the  free  surface  and  branching  as  they  go.  These  fibres  are  the  processes 
of  the  cells  of  Purkinje.    (2.)  The  Cells  of  Purkinje  (p).    These  are  a 


118 


HAND-BOOK  OF  PHYSIOLOGY. 


single  layer  of  branched  nerve-cells,  which  give  oif  a  single  unbranched 
process  downAvard,  and  numerous  processes  up  into  the  external  layer,  some 
of  which  become  continuous  with  the  scattered  corpuscles.  (3.)  The 
granular  layer  (g),  consisting  of  immense  numbers  of  corpuscles  closely 
resembling  those  of  the  nuclear  layers  of  the  retina.  (4. )  Nerve  fibre 
layer  (/).  Bundles  of  nerve-fibres  forming  the  white  matter  of  the 
cerebellum,  which,  from  its  branched  appearance,  has  been  named  the 
* 'arbor  yH^." 

Functions. — The  physiology  of  the  Cerebellum  may  be  considered  in 
its  relation  to  sensation,  voluntary  motion,  and  the  instincts  or  higher 
faculties  of  the  mind.  Its  supposed  functions,  like  those  of  every  other 
part  of  the  nervous  system,  have  been  determined  by  physiological  experi- 
ment, by  pathological  observation,  and  by  its  comparative  anatomy. 

(1.)  It  is  itself  insensible  to  i^^itation,  and  may  be  all  cut  away  with- 
out eliciting  signs  of  pain  (Longet).  Its  removal  or  disorganization  by 
disease  is  also  generally  unaccompanied  by  loss  or  disorder  of  sensibility; 
animals  from  which  it  is  removed  can  smell,  see,  hear,  and  feel  pain,  to 
all  appearance,  as  perfectly  as  before  (Elourens;  Magendie).  Yet,  if  any 
of  its  crura  be  touched,  pain  is  indicated;  and,  if  the  restif orm  tracts  of 
the  medulla  oblongata  be  irritated,  the  most  acute  suffering  appears  to 
be  produced.  So  that,  although  the  restif  orm  tracts  of  the  medulla 
oblongata,  which  themselves  appear  so  sensitive,  enter  the  cerebellum,  it 
cannot  be  regarded  as  a  principal  organ  of  sensation. 

(2.)  Co-ordination  of  Movements. — In  reference  to  motion,  the  experi- 
ments of  Longet  and  many  others  agree  that  no  irritation  of  the  cerebel- 
lum produces  movement  of  any  kind.  Eemarkable  results,  however,  are 
produced  by  removing  parts  of  its  substance.  Flourens  (whose  experi- 
ments have  been  confirmed  by  those  of  Bouillaud,  Longet,  and  others) 
extirpated  the  cerebellum  in  birds  by  successive  layers.  Feebleness  and 
want  of  harmony  of  muscular  movements  were  the  consequence  of  remov- 
ing the  superficial  layers.  When  he  reached  the  middle  layers,  the  ani- 
mals became  restless  without  being  convulsed;  their  movements  were  vio- 
lent and  irregular,  but  their  sight  and  hearing  were  perfect.  By  the 
time  that  the  last  portion  of  the  organ  was  cut  away,  the  animals  had 
entirely  lost  the  powers  of  springing,  flying,  Avalking,  standing,  and  pre- 
serving their  equilibrium.  When  an  animal  in  this  state  was  laid  upon 
its  back,  it  could  not  recover  its  former  posture,  but  it  fluttered  its  wings, 
and  did  not  lie  in  a  state  of  stupor;  it  saw  the  blow  that  threatened  it, 
and  endeavored  to  avoid  it.  Volition  and  sensation,  therefore,  were  not 
lost,  but  merely  the  faculty  of  combining  the  actions  of  the  muscles;  and 
the  endeavors  of  the  aninuil  to  maintain  its  balance  were  like  those  of  a 
drunken  man. 

The  experiments  afforded  t]u>  same  results  when  roiieated  on  classes 
of  animals;  and  from  them  and'  the  others  before  referred  to,  Klourens 


THE  NERVOUS  SYSTEM. 


119 


inferred  that  the  cerebellum  belongs  neither  to  the  sensory  nor  the  intel- 
lectual apparatus;  and  that  it  is  not  the  source  of  voluntary  movements, 
although  it  belongs  to  the  motor  apparatus;  but  is  the  organ  for  the  co- 
ordination of  the  voluntary  movements,  or  for  the  excitement  of  the 
comUnecl  action  of  muscles. 

Such  evidence  as  can  be  obtained  from  cases  of  disease  of  this  organ 
confirms  the  view  taken  by  Flourens;  and,  on  the  whole,  it  gains  sup- 
port from  comparative  anatomy;  animals  whose  natural  movements 
require  most  frequent  and  exact  combinations  of  muscular  actions  being 
those  whose  cerebella  are  most  developed  in  proportion  to  the  spinal  cord. 

Foville  supposed  that  the  cerebellum  is  the  organ  of  muscular  sense, 
i.e.,  the  organ  by  which  the  mind  acquires  that  knowledge  of  the  actual 
state  and  position  of  the  muscles  which  is  essential  to  the  exercise  of  the 
will  upon  them;  and  it  must  be  admitted  that  all  the  facts  just  referred 
to  are  as  well  explained  on  this  hypothesis  as  on  that  of  the  cerebellum 
being  the  organ  for  combining  movements.  A  harmonious  combination 
of  muscular  actions  must  depend  as  much  on  the  capability  of  appreciating 
the  condition  of  the  muscles  with  regard  to  their  tension,  and  to  the 
force  with  which  they  are  contracting,  as  on  the  power  which  any  special 
nerve-centre  may  possess  of  exciting  them  to  contraction.  And  it  is 
because  the  power, of  such  harmonious  movement  would  be  equally  lost, 
whether  the  injury  to  the  cerebellum  involved  injury  to  the  seat  of  mus- 
cular sense,  or  to  the  centre  for  combining  muscular  actions,  that  experi- 
ments on  the  subject  afford  no  proof  in  one  direction  more  than  the  other. 

The  theory  once  believed,  that  the  cerebellum  is  the  organ  of  sexual 
passion,  has  been  long  disproved. 

Forced  Movements. — The  influence  of  each  half  of  the  cerebellum 
is  directed  to  muscles  on  the  opposite  side  of  the  body;  and  it  would  appear 
that  for  the  right  ordering  of  movements,  the  actions  of  its  two  halves 
must  be  always  mutually  balanced  and  adjusted.  For  if  one  of  its  crura, 
or  if  the  pons  on  either  side  of  the  middle  line,  be  divided,  so  as  to  cut  oif 
the  medulla  oblongata  and  spinal  cord  the  influence  of  one  of  the  hemi- 
spheres of  the  cerebellum,  strangely  disordered  movements  ensue  (forced 
movements).  The  animals  fall  down  on  the  side  opposite  to  that  on  which 
the  crus  cerebelli  has  been  divided,  and  then  roll  over  continuously  and 
repeatedly;  the  rotation  being  always  round  the  long  axis  of  their  bodies, 
and  generally  from  the  side  on  which  the  injury  has  been  inflicted.  The 
rotations  sometimes  take  place  with  much  rapidity;  as  often,  according  to 
Magendie,  as  sixty  times  in  a  minute,  and  may  last  for  several  days. 
Similar  movements  have  been  observed  in  men;  as  by  Serres  in  a  man  in 
whom  there  was  apoplectic  eifusion  in  the  right  crus  cerebelli;  and  by 
Belhomme  in  a  woman  in  whom  an  exostosis  pressed  on  the  left  crus. 
They  may,  perhaps,  be  explained  by  assuming  that  the  division  or  injury 
of  the  crus  cerebelli  produces  paralysis  or  imperfect  and  disorderly  move- 


120 


HAND-BOOK  OF  PHYSIOLOGY. 


ments  of  the  opposite  side  of  the  body;  the  animal  falls,  and  then,  strug- 
gling with  the  disordered  side  on  the  ground,  and  striving  to  rise  with  the 
other,  pushes  itself  over;  and  so  again  and  again,  with  the  same  act,  rotates 
itself.  Such  movements  cease  when  the  other  crus  cerebelli  is  divided;  but 
probably  only  because  the  paralysis  of  the  body  is  thus  made  almost  com- 
plete. Other  varieties  of  forced  movements  have  been  observed,  especially 
those  named  "circus  movements,"  when  the  animal  operated  upon  moves 
round  and  round  in  a  circle;  and  again  those  in  which  the  animal  turns 
over  and  over  in  a  series  of  somersaults.  Nearly  all  these  movements  may 
result  on  section  of  one  or  other  of  the  following  parts;  viz.,  crura  cere- 
bri, medulla,  pons,  cerebellum,  corpora  quadrigemina,  corpora  striata,  optic 
thalami,  and  even,  it  is  said,  of  the  cerebral  hemispheres. 

The  Cerebrum. 

The  Cerebrum  (composed  of  two  so-called  Cerebral  hemispheres)  is 
placed  in  connection  with  the  Pons  and  Medulla  oblongata  by  its  two 
crura  or  peduncles  (IIl.,  Eig.  326):  it  is  connected  with  the  cerebellum  by 
the  processes  called  superior  crura  of  the  cerebellum,  or  processus  a  cere- 
hello  ad  testes,  and  by  a  layer  of  grey  matter,  called  the  valve  of  Vieussens, 
which  lies  between  these  processes,  and  extends  from  the  inferior  vermiform 
process  of  the  cerebellum  to  the  corpora  quadrigemina  of  the  cerebrum. 
These  parts,  which  thus  connect  the  cerebrum  with  the  other  principal 
divisions  of  the  cerebro-spinal  system,  may,  therefore,  be  regarded  as  the 
continuation  of  the  cerebro-spinal  axis  or  column;  on  which,  as  a  kind 
of  offset  from  the  main  nerve-path,  the  cerebellum  is  placed;  and  on 
the  further  continuation  of  which  in  the  direct  line,  is  placed  the  cerebrum 
(Fig.  331). 

The  Cerebrum  is  constructed,  like  the  other  chief  divisions  of  the 
cerebro-spinal  system,  of  grey  (vesicular  and  fibrous)  and  white  (fibrous) 
matter;  and,  as  in  the  case  of  the  Cerebellum  (and  unlike  the  spinal  cord 
and  medulla  oblongata),  the  grey  matter  {cortex)  is  external,  and  forms  a 
capsule  or  covering  for  the  white  substance.  For  the  evident  purpose  of 
increasing  its  amount  without  undue  occupation  of  space,  the  grey  matter 
is  variously  infolded  so  as  to  form  the  cerebral  convolutions. 

Gonvolutio7is  of  the  Cerehrim. — For  convenience  of  description,  the 
surface  of  the  brain  has  been  divided  into  five  lobes  (Gratiolet). 

1.  Frontal  (F.,  Figs.  332,  333),  limited  behind  by  the  fissure  of  Rolando 
(central  fissure),  and  beneath  by  the  fissure  of  Sylvius.  Its  surface  con- 
sists of  three  main  convolutions,  which  are  approximately  horizontal  in 
direction  and  arc  broken  up  into  numerous  secondary  gyri.  They  are 
termed  the  su])eri()r,  middle,  and  inferior  frontal  convolutions.  In  addi- 
tion, the  frontal  lobe  contains,  at  its  })osteri()r  });irt,  a  convolution  which 
runs  upward  almost  vertically  ("ascending  frontal"),  and  is  bounded  in 
front  by  a  fissure  termed  the  prsecentral,  behind  by  that  gf  Rolando. 


THE  NERVOUS  SYSTEM. 


121 


Fig.  331.— Plan  in  outline  of  the  encephalon,  as  seen  from  the  riprht  side,         The  parts  are  rep- 
resented as  separated  from  one  another  somewhat  more  than  natural,  so  as  to  show  their  coimec- 
-  tions.   A,  cerebrum;  /,  g,  h,  its  anterior,  middle,  and  posterior  lobes;  e,  fissure  of  Sylvius:  B,  cere- 
bellum; C,  pons  VaroUi;  D,  medulla  oblongata;  a,  peduncles  of  the  cerebrum;  b,  c,  d,  superior  mid- 
dle, and  inferior  peduncles  of  the  cerebellum.   (From  Quain.) 


Fig.  332.— Lateral  view  of  the  brain  (semi-diagrammatic).  F,  Frontal  lobe;  P,  Parietal  lobe;  O, 
Occipital  lobe;  T,  Temporo-sphenoidal  lobe;  S,  fissure  of  Sylvius;  S',  horizontal,  S",  ascending  ramus 
of  the  same;  c,  sulcus  centralis  (fissure  of  Rolando);  A,  ascending  frontal;  B,  ascending  parietal 
convolution;  Fl.  superior;  F2,  middle;  F3,  inferior  frontal  convolutions;  fl,  superior;  f 2.  inferior 
frontal  sulcus;  f3,  prae-central  sulcus;  PI,  superior  parietal  lobule ;  P2,  inferior  parietal  lobule  con- 
sisting of  P2,  supramarginal  gyrus,  and  P2',  angular  gyrus;  ip,  interparietal  sulcus;  cm.  termination 
of  caUoso-marginal  fissiire ;  01,  first,  02,  second,  03,  third  occipital  convolutions;  po,  parieto-occipi- 
tal  fissure;  o,  transverse  occipital  fissure ;  o2,  sulcus  occipitahs  inferior;  Tl,first.T2,  second,  T3,  third 
temporo-sphenoidal  convolutions;  tl,  first,  t2,  second  temporo-sphenoidal  fissures.  (Ecker.) 


122 


HAND-BOOK  OF  PHYSIOLOGY. 


I 


2.  Parietal  (P.).  This  lobe  is  bounded  in  front  by  the  fissure  of  Eo- 
lando,  behind  by  the  external  perpendicular  fissure  (parieto-occipital),  and 
below  by  the  fissure  of  S3dvius.  Behind  the  fissure  of  Eolando  is  the  "as- 
cending parietaF^  convolution,  which  swells  out  at  its  upper  end  into  what 
is  termed  the  superior  parietal  lobule.  The  superior  parietal  lobule  is 
separated  from  the  inferior  parietal  lobule  by  the  intra- parietal  sulcus. 
The  inferior  parietal  lobule  (pli  courbe)  is  situated  at  the  posterior  and 
upper  end  of  the  fissure  of  Sylvius;  it  consists  of  {a)  an  anterior  part  (supra- 
marginal  convolution)  which  hooks  round  the  end  of  the  fissure  of  Sylvius, 
and  joijis  the  superior  temporal  convolution,  and  a  posterior  part  (b)  (angu- 
lar gyrus)  which  hooks  round  into  the  middle  temporal  convolution. 


Fig.  333.— View  of  the  brain  from  above  (semi-diagrammatic).  SI,  end  of  horizontal  ramus  of  As- 
sure of  Sylvius.   The  other  letters  refer  to  the  same  parts  as  in  Fig.  332.  (Ecker.) 


3.  Temporo-sphenoidal  (T. ),  contains  three  well-marked  convolutions, 
parallel  to  each  other,  termed  the  superior,  middle,  and  inferior  temporal. 
The  superior  and  middle  are  separated  by  the  parallel  fissure. 

4.  Occipital  (0.).  This  lobe  lies  behind  the  external  perpendicular  or 
parieto-occipital  fissure,  and  contains  three  convolutions,  termed  the  supe- 
rior, middle,  and  inferior  occipital.  They  are  often  not  well  marked.  In 
man,  the  external  parieto-occipital  fissure  is  only  to  be  distinguished  as  a 
notch  in  the  inner  edge  of  the  hemisphere;  below  this  it  is  quite  obliter- 
ated by  the  four  annectent  gyri  (plis  de  passage)  which  run  nearly  hori- 
zontally. The  upper  two  connect  the  parietal,  and  the  lower  two  the  tem- 
poral with  the  occipital  lobe. 

5.  T^he  central  lohe,  or  island  of  Eeil,  which  contains  a  number  of 
radiating  convolutions  (gyri  operti). 

The  internal  surface  (^Fig.  334)  contains  the  following  gyri  and  sulci: 
Gyrus  fornicatus,  a  long  curved  convohition,  paniUol  to  ;ind  curving 
round  the  corpus  callosiini,  and  swelling  out  at  its  hinder  and  upper  end 


THE  NERVOUS  SYSTEM. 


123 


into  the  quadrate  lobule  (praecuneus),  which  is  continuous  with  the  superior 
parietal  lobule  on  the  external  surface. 

Marginal  convolution  runs  parallel  to  the  preceding^  and  occupies  the 
space  between  it  and  the  edge  of  the  longitudinal  fissure. 

The  two  convolutions  are  separated  by  the  calloso -marginal  fissure. 

The  internal  perpendicular  fissure  is  well  marked^,  and  runs  downward 
to  its  junction  with  the  calcarine  fissure:  the  wedge-shaped  mass  inter- 
vening between  these  two  is  termed  the  cuneus.  The  calcarine  fissure 
corresponds  to  the  projection  into  the  posterior  cornu  of  the  lateral  ven- 
tricle, termed  the  Hippocampus  minor.  The  temporo-splienoidal  lohe  on 
its  internal  aspect  is  seen  to  end  in  a  hook  (^uncinate  gyrus).  The  notch 
round  which  it  curves  is  continued  up  and  back  as  the  dentate  or  hippo- 


Fig.  334.— View  of  the  right  hemisphere  in  the  median  aspect  (semi-diagrammatic).  CC,  corpus 
callosvim  longitudinally  divided;  Gf,  gyrus  fornicatus;  H,  gyrus  hippocampi;  h,  sulcus  hippocampi; 
U,  uncinate  gyrus;  cm,  calloso-marginal  fissure ;  Fl,  median  aspect  of  first  frontal  convolution;  c, 
terminal  portion  of  sulcus  centralis  (fissure  of  Rolando);  A,  ascending  frontal;  B,  ascending  parietal 
convolution;  PI',  praecuneus;  Oz,  cuneus;  po,  parieto-occipital  fissure;  o,  sulcus  occipitalis  transver- 
sus;  oc,  calcarine  fissure;  oc',  superior;  oc",  inferior  ramus  of  the  same;  D,  gyrus  descendens;  T4, 
gyrus  occipito-temporahs  lateralis  (lobulus  f usif ormis) ;  T5,  gyrus  occipito-temporalis  medialis  (lobulus 
lingualis).  (Ecker.) 

campal  sulcus;  this  fissure  underlies  the  projection  of  the  hippocampus 
major  within  the  brain.  There  are  three  internal  tempore -occipital  con- 
volutions, of  which  the  superior  and  inferior  ones  are  usually  well  marked, 
the  middle  one  generally  less  so. 

The  collateral  fissure  (corresponding  to  the  eminentia  collateralis)  forms 
the  lower  boundary  of  the  superior  temporo-occipital  convolution.  All  the 
above  details  will  be  found  indicated  in  the  diagrams  (Fig.  332,  333,  334). 

Structure. — The  cortical  grey  matter  of  the  brain  consists  of  five 
layers  (Meynert)  (Fig.  335). 

1.  Superficial  layer  with  abundance  of  neuroglia  and  a  few  small  multi- 
polar ganglion- cells.  2.  A  large  number  of  closely  packed  small  ganglion- 
cells  of  pyramidal  shape.  3.  The  most  important  layer,  and  the  thickest 
of  all:  it  contains  many  large  pyramidal  ganglion-cells,  each  with  a  process 
running  off  from  the  apex  vertically  toward  the  free  surface,  and  lateral 
processes  at  the  base  which  are  always  branched.    Also  a  median  process 


124 


HAND-BOOK  OF  PHYSIOLOGY. 


from  the  base  of  each  cell  which  is  unbranched  and  becomes  continuous 
with  the  axis-cylinder  of  a  nerve-fibre.  4.  Numerous  ganglion-cells: 
termed  the  * 'granular  formation^^  by  Meynert.  5.  Spindle-shaped  and 
branched  ganglion -cells  of  moderate  size  arranged  chiefly  parallel  to  the 
free  surface  {vide  Fig.  335). 


Fig.  335.  Fig.  ;>37. 

Fig.  335.— The  layers  of  the  cortical  grey  matter  of  the  cerebrum.  (Meynert.) 
Fig.  337.— [Drawn  by  G.  Munro  Smith  from  annnonium  biehroniate  preparations  by  E.  C. 
Bousfield.J 

Ac(!ording  to  recent  observations  by  Bousfield,  tlie  fibres  of  the  medullary 
centre  become  connected  with  tlie  multipolar  ganglion  cells  of  the  fourth 
layer,  and,  from  these  latter,  branches  i)ass  to  the  angles  at  the  bases  of  the 
pyramidal  colls  of  the  third  layer  of  the  cortex  (Fig.  ooT,  a).  From  the 
apices  of  the  i)yramidal  cells,  the  axis-cylinder  processes  pass  upward  for  a 


THE  NERVOUS  SYSTEM. 


125 


considerable  distance,  and  finally  terminate  in  ovoid  corpuscles  (Fig.  336) 
closely  resembling,  and  homologous  with,  the  corpuscles  in  which  the  ulti- 
mate ramifications  of  the  branched  cells  of  Purkinje  in  the  cerebellum 
terminate.  Thus  it  would  seem  that  the  large  pyramidal  cells  of  the  third 
layer  are  themselves  homologous  with  the  cells  of  Purkinje  in  the  cere- 
bellum. 


The  white  matter  of  the  brain,  as  of  the  spinal  cord,  consists  of  bundles 
of  medullated,  and,  in  the  neighborhood  of  the  grey  matter,  of  non- 
medullated  nerve-fibres,  which,  however,  as  is 
.the  case  in  the  central  nervous  system  generally, 
have  no  external  nucleated  nerve -sheath,  which 
are  held  together  by  delicate  connective  tissue. 
The  size  of  the  fibres  of  the  brain  is  usually  less 
than  that  of  the  fibres  of  the  spinal  cord:  the 
average  diameter  of  the  former  being  about 
T7ST0  of  an  inch. 

Chemical  Composition. — The  chemistry 
of  ner  re  and  nerve  cells  has  been  chiefly  studied 
in  the  brain  and  spinal  cord.  Nerve  matter 
contains  several  albuminous  and  fatty  bodies 
(cerebrin,  lecithin,  and  some  others),  also  fatty 
matter  which  can  be  extracted  by  ether  (in- 
cluding cholesterin)  and  various  salts,  especially 
Potassium  and  Magnesium  phosphates,  which 
exist  in  larger  quantity  than  those  of  Sodium 
and  Calcium.  Yolk  of  egg  resembles  cerebral 
substance  very  closely  in  its  chemical  composi- 
tion; milk  and  muscle  also  come  very  near  it. 


Fig. 
zontal 
brain. 


The  great  relative  and  absolute  size  of  the 
Cerebral  hemispheres  in  the  adult  man,  masks 
to  a  great  extent  the  real  arrangement  of  the 
several  parts  of  the  brain,  which  is  illustrated  in 
the  two  accompanying  diagrams.  Prom  these 
it  is  apparent  that  the  parts  of  the  brain  are 
disposed  in  a  linear  series,  as  follows  (from  be- 
fore backward) :  olfactory  lobes,  cerebral  hemis- 
pheres, optic  thalami,  and  third  ventricle,  cor- 
pora quadrigemina,  or  optic  lobes,  cerebellum, 
medulla  oblongata. 

This  linear  arrangement  of  parts  actually 
occurs  in  the  human  foetus  (see  Chapter  on 
permanent  in  some  of  the  lower  Vertebrata,  e  ^  ^ 
cerebral  hemispheres  are  represented  by  a  pair  of"  ganglia  intervening  be 
tween  the  olfactory  and  the  optic  lobes,  and  considerably  smaller  than  the 
latter.  In  Amphibia  the  cerebral  lobes  are  further  developed,  and  are 
larger  than  any  of  the  other  ganglia. 


Diagrammatic  hori- 
section  of  a  Vertebrate 
The  figures  serve  both 
for  this  and  the  next  diagram. 
Mb,  mid  brain:  whathes  in  front 
of  this  is  the  fore,  and  what  hes 
behind,  the  hind  brain;  Lt,  la- 
mina terminalis;  Olf,  olfactory- 
lobes;  Hmp,  hemispheres;  Th. 
E,  thalamencephalon ;  Pa,  pineal 
gland;  Py,  pituitary  body;  F.M, 
foramen  of  Munro;  cs,  corpus 
striatum;  Th,  optic  thalamus; 
CC,  crura  cerebri:  the  mass  lying 
above  the  canal  represents  the 
corpora  quadrigemina;  Cb,  cere- 
bellum; I— IX.,  the  nine  pairs  of 
cranial  nerves:  1,  olfactory  ven- 
tricle; 2,  lateral  ventricle;  3,  third 
ventricle;  4, foiu-th ventricle;  +, 
iter  a  tertio  ad  quartum  ventri- 
culum.  (Huxley.) 

Development),  and  it  is 
g.,  Fishes,  in  which  the 


126 


HAND-BOOK  OF  PHYSIOLOGY. 


In  Reptiles  and  Birds  the  cerebral  ganglia  attain  a  still  further  de- 
velopment, and  in  Mammalia  the  cerebral  hemispheres  exceed  in  weight 
all  the  rest  of  the  brain.  As  we  ascend  the  scale,  the  relative  size  of  the 
cerebrum  increases,  till  in  the  higher  apes  and  man  the  hemispheres, 
which  commenced  as  two  little  lateral  buds  from  the  anterior  cerebral 
vesicle,  have  grown  upward  and  backward,  completely  covering  in  and 
hiding  from  view  all  the  rest  of  the  brain.  At  the  same  time  the  smooth 
surface  of  the  brain,  in  many  lower  Mammalia,  such  as  the  rabbit,  is  re- 
placed by  the  labyrinth  of  convolutions  of  the  human  brain. 

Weight  of  the  Brain. — The  brain  of  an  adult  man  weighs  from  48  to 
50  oz. — or  about  3  lbs.  It  exceeds  in  absolute  weight  that  of  all  the 
lower  animals  except  the  elephant  and  whale.  Its  weight,  relatively  to 
that  of  the  hocly,  is  only  exceeded  by  that  of  a  few  small  birds  and  some 
of  the  smaller  monkeys.  In  the  adult  man  it  ranges  from  — -^^  of  the 
body  weight. 

Variations.  Age. — In  a  new-born  child  the  brain  (weighing  10 — 14  oz.) 
is      of  the  body  weight.    At  the  age  of  7  years  the  weight  of  the  brain 


Fig.  339.— Longitudinal  and  vertical  Diagrammatic  section  of  a  Vertebrate  brain.  Letters  as  be- 
fore.  Lamina  terminalis  is  represented  by  the  strong  black  line  joining  Pn  and  Py.  (Huxley.) 

already  averages  40  oz.,  and  about  14  years  the  brain  not  unfrequently 
reaches  the  weight  of  48  oz.  Beyond  the  age  of  40  years  the  weight 
slowly  but  steadily  declines  at  the  rate  of  about  1  oz.  in  10  years. 

Sex. — The  average  weight  of  the  female  brain  is  less  than  the  male; 
and  this  difference  persists  from  birth  throughout  life.  In  the  adult  it 
amounts  to  about  5  oz.  Thus  the  average  weight  of  an  adult  woman's 
brain  is  about  44  oz. 

Intelligence. — The  brains  of  idiots  are  generally  much  below  the  aver- 
age, some  weighing  less  than  16  oz.  Still  the  facts  at  present  collected 
do  not  warrant  more  than  a  very  general  statement,  to  which  there  are 
numerous  exceptions,  that  the  brain  weight  corresponds  to  some  extent 
with  the  degree  of  intelligence.  There  can  be  little  doubt  that  the  com- 
2)lexity  and  depth  of  the  convolutions,  which  indicate  the  area  of  the  grey 
matter  of  the  cortex,  correspond  with  the  degree  of  intelligence  (R. 
Wagner). 

Weight  of  the  Spinal  Cord. — The  spinal  cord  of  man  weighs  from 
1 — 11  oz. ;  its  weight  relatively  to  the  brain  is  about  1  :  36.  As  Ave  descend 
the  scale,  this  ratio  constantly  increases  till  in  the  mouse  it  is  1  :  4.  In 
cold-blooded  animals  the  relation  is  reversed,  the  spinal  cord  is  the  heavier 
and  more  important  organ.    In  the  newt,  2:1;  and  in  the  lamprey,  75  : 1. 

Distinrtive  (^liararfcrs  of  the  Ihnnan  Brain. — The  following  character 
distinguish  the  brtfin  of  m((u  (oid  (tpvx  from  those  of  all  oilier  animals,  (a.) 


THE  NERVOUS  SYSTEM. 


127 


The  rudimentary  condition  of  the  olfactory  lobes,  (b).  A  perfectly  defined 
fissure  of  Sylvius,  (c).  A  posterior  lobe  completely  covering  the  cerebel- 
lum, (d).  The  presence  of  posterior  cornua  in  the  lateral  ventricles 
(Gratiolet). 

The  most  distinctive  points  in  the  human  train,  as  contrasted  with 
that  of  apes,  are: — (1).  The  much  greater  size  and  weight  of  the  whole 
brain.  The  brain  of  a  full-grown  gorilla  weighs  only  about  15  oz.,  which 
is  less  than  \  the  weight  of  the  human  adult  male  brain,  and  barely 
exceeds  that  of  the  human  infant  at  birth.  (2).  The  much  greater  com- 
plexity of  the  convolutions,  especially  the  existence  in  the  human  brain  of 
tertiary  convolutions  in  the  sides  of  the  fissures.    (3).  The  greater  relative 


Fig.  340.— Brain  of  the  Orang,  %  natural  size,  showing  the  arrangement  of  the  convolutions.  8y^ 
fissure  of  Sylvius;  J2,  fissure  of  Rolando;  iJP,  external  perpendicular  fissure;  OZ/,  olfactory  lobe; 
Cft,  cerebellum ;  PF,  pons  Varolii;  ilfO,  medulla  oblongata.  As  contrasted  with  the  human  brain, 
the  frontal  lobe  is  short  and  small  relatively,  the  fissure  of  Sylvius  is  oblique,  the  temporo-sphenoidal 
lobe  very  prominent,  and  the  external  perpendicular  fissure  very  well  marked.  (Gratiolet.) 


size  and  complexity,  and  the  blunted  quadrangular  contour  of  the  frontal 
lobes  in  man,  which  are  relatively  both  broader,  longer,  and  higher,  than 
in  apes.  In  apes  the  frontal  lobes  project  keel-like  (rostrum)  between  the 
olfactory  bulbs.  (4).  The  much  greater  prominence  of  the  temporo- 
sphenoidal  lobe  in  apes.  (5).  The  fissure  of  Sylvius  is  nearly  horizontal 
in  man,  while  in  apes  it  slants  considerably  upward.  (6).  The  distinct- 
ness of  the  external  perpendicular  fissure,  which  in  apes  is  a  well-defined 
almost  vertical  "slash,"  while  in  man  it  is  almost  obscured  by  the  an- 
nectent  gyri  (Eolleston). 

Most  of  the  above  points  are  shown  in  the  accompanying  figure  of  the 
brain  of  the  Orang. 

Functions. — (1.)  The  Cerebral  hemispheres  are  the  organs  by  which 
are  perceived  those  clear  and  more  impressive  sensations  which  can  be 
retained,  and  regarding  which  we  can  judge.  (2.)  The  Cerebrum  is  the 
organ  of  the  will  in  so  far  at  least  as  each  act  of  the  will  requires  a  de- 
liberate, however  quick  determination.    (3.)  It  is  the  means  of  retaining 


128 


HAND-BOOK  OF  PHYSIOLOGY. 


impressions  of  sensible  things,  and  reproducing  them  in  subjective  sensa- 
tions and  ideas.  (4.)  It  is  the  medium  of  all  the  higher  emotions  and 
feelings,  and  of  the  faculties  of  judgment,  understanding,  memory,  reflec- 
tion, induction,  imagination  and  the  like. 

Evidence  regarding  the  physiology  of  the  cerebral  hemispheres  has 
been  obtained,  as  in  the  case  of  other  parts  of  the  nervous  system,  from  the 
study  of  Comparative  Anatomy,  from  Pathology,  and  from  Experiments 
on  the  lower  animals.  The  chief  evidences  regarding*  the  functions  of 
the  Cerebral  hemispheres  derived  from  these  various  sources,  are  briefly 
these: — 1.  Any  severe  injury  of  them,  such  as  a  general  concussion,  or 
sudden  pressure  by  apoplexy,  may  instantly  deprive  a  man  of  all  power  of 
manifesting  externally  any  mental  faculty.  2.  In  the  same  general  pro- 
portion as  the  higher  mental  faculties  are  developed  in  the  Vertebrate  ani- 
mals, and  in  man  at  different  ages  and  in  different  individuals,  the  more 
is  the  size  of  the  cerebral  hemispheres  developed  in  comparison  with  the 
rest  of  the  cerebro-spinal  system.  3.  No  other  part  of  the  nervous  system 
bears  a  corresponding  proportion  to  the  development  of  the  mental  facul- 
ties. 4.  Congenital  and  other  morbid  defects  of  the  cerebral  hemisphere 
are,  in  general,  accompanied  by  corresponding  deficiency  in  the  range  or 
power  of  the  intellectual  faculties  and  the  highsr  instincts.  5.  Removal 
of  the  cerebral  hemispheres  in  one  of  the  lower  animals  produces  effects 
corresponding  with  what  might  be  anticipated  from  the  foregoing  facts. 
The  animal,  although  retaining  mere  sensation,  and  the  power  of  per- 
forming even  complicated  reflex  acts,  remains  in  a  state  of  stupor,  and 
performs  no  voluntary  movement  of  any  kind.    (See  below.) 

Effects  of  the  Removal  of  the  Cerebrum. — The  removal  of  the 
cerebrum  in  the  lower  animals  appears  to  reduce  them  to  the  condition  of 
a  mechanism  withoat  spontaneity.  A  pigeon  from  which  the  cerebrum 
has  been  removed  will  remain  motionless  and  apparently  unconscious 
unless  disturbed.  When  disturbed  in  any  way  it  soon  recovers  its  former 
position;  when  thrown  into  the  air  it  flies. 

In  the  case  of  the  frog,  when  the  cerebral  lobes  have  been  removed,, 
the  animal  appears  similarly  deprived  of  all  power  of  spontaneous  move- 
ment. But  it  sits  up  in  a  natural  attitude,  breathing  quietly;  when 
pricked  it  jumps  away;  when  thrown  into  the  water  it  swims;  when  placed 
upon  the  palm  of  the  hand  it  remains  motionless,  although,  if  the  hand 
be  gradually  tilted  over  till  the  frog  is  on  the  point  of  losing  his  balance, 
he  will  crawl  up  till  he  regains  his  equilibrium,  and  comes  to  be  perched 
quite  on  the  edge  of  the  hand.  This  condition  contrasts  with  that  result- 
ing from  the  removal  of  the  entire  brain,  leaving  only  the  spinal  cord;  in 
this  case  only  the  simpler  reflex  actions  can  take  place.  The  frog  does 
not  breathe,  he  lies  flat  on  the  table  instead  of  sitting  up;  when  thrown 
into  a  vessel  of  water  he  sinks  to  the  bottom;  when  his  legs  are  pinched 
he  kicks  out,  but  docs  not  leap  away. 


THE  NERVOUS  SYSTEM. 


129 


Unilateral  action. — Eespecting  tlie  mode  in  which  the  brain  dis- 
charges its  functions,  there  is  no  evidence  whatever.  But  it  appears 
that,  for  all  but  its  highest  intellectual  acts,  one  of  the  cerebral  hemi- 
spheres is  sufficient.  For  numerous  cases  are  recorded  in  which  no 
mental  defect  was  observed,  although  one  cerebral  hemisphere  was 
so  disorganized  or  atrophied  that  it  could  not  be  supposed  capable  of 
discharging  its  functions.  The  remaining  hemisphere  was,  in  these  cases, 
adequate  to  the  functions  generally  discharged  by  both;  but  the  mind  does 
not  seem  in  any  of  these  cases  to  have  been  tested  in  very  high  intellectual 
exercises;  so  that  it  is  not  certain  that  one  hemisphere  will  suffice  for 
these.  In  general,  the  mind  combines,  as  one  sensation,  the  impressions 
which  it  derives  from  one  object  through  both  hemispheres,  and  the  ideas 
to  which  the  two  such  impressions  give  rise  are  single.  In  relation  to 
common  sensation  and  the  etfort  of  the  will,  the  impressions  to  and  from 
the  hemispheres  of  the  brain  are  carried  across  the  middle  line;  so  that  in 
destruction  or  compression  of  either  hemisphere,  whatever  effects  are  pro- 
duced in  loss  of  sensation  or  voluntary  motion,  are  observed  on  the  side 
of  the  body  opposite  to  that  on  which  the  brain  is  injured. 

Localization  of  Functions. — In  speaking  of  the  cerebral  hemi- 
SBpheres  as  the  so-called  organs  of  the  mind,  they  have  been  regarded  as  if 
they  were  single  organs,  of  which  all  parts  are  equally  appropriate  for  the 
exercise  of  each  of  the  mental  faculties.  But  it  is  possible  that  each 
faculty  has  a  special  portion  of  the  brain  appropriated  to  it  as  its  proper 
organ.  For  this  theory  the  principal  evidences  are  as  follows: — 1.  That 
it  is  in  accordance  with  the  physiology  of  the  compound  organs  or  systems 
in  the  body,  in  which  each  part  has  its  special  function;  as,  for  example, 
of  the  digestive  system,  in  which  the  stomach,  liver,  and  other  organs 
perform  each  their  separate  share  in  the  general  process  of  the  digestion 
of  the  food.  2.  That  in  different  individuals  the  several  mental  func- 
tions are  manifested  in  very  different  degrees.  Even  in  early  childhood, 
before  education  can  be  imagined  to  have  exercised  any  influence  on  the 
mind,  children  exhibit  various  dispositions — each  presents  some  predom- 
inant propensity,  or  evinces  a  singular  aptness  in  some  study  or  pursuit; 
and  it  is  a  matter  of  daily  observation  that  every  one  has  his  peculiar 
talent  or  propensity.  But  it  is  difficult  to  imagine  how  this  could  be  the 
case,  if  the  manifestation  of  each  faculty  depended  on  the  whole  of  the 
brain;  different  conditions  of  the  whole  mass  might  affect  the  mind  gen- 
erally, depressing  or  exalting  all  its  functions  in  an  equal  degree,  but, 
could  not  permit  one  faculty  to  be  strongly  and  another  weakly  mani- 
fested. 3.  The  plurality  of  organs  in  the  brain  is  supported  by  the 
phenomena  of  some  forms  of  mental  derangement.  It  is  not  usual  for 
all  the  mental  faculties  in  an  insane  person  to  be  equally  disordered;  it 
often  happens  that  the  strength  of  some  is  increased,  while  that  of  others 
IS  diminished;  and  in  many  cases  one  function  only  of  the  brain  is 
Vol.  II.— 9. 


loO  HAXD-BOOK  OF  PHYSIOLOGY. 

deranged,  while  all  the  rest  are  performed  in  a  natnral  inanner.  4.  The 
same  opinion  is  snpported  by  the  fact  that  the  several  mental  faculties 
are  developed  to  their  greatest  strength  at  different  periods  of  life,  some 
being  exercised  with  great  energy  in  childhood,  others  only  in  adult  age; 
and  that,  as  their  energy  decreases  in  old  age,  there  is  not  a  gradual  and 
equal  diminution  of  power  in  all  of  them  at  once,  but,  on  the  contrary,  a 
diminution  in  one  or  more,  while  others  retain  their  full  strength,  or 
even  increase  in  power.  5.  The  plurality  of  cerebral  organs  appears  to  be 
indicated  by  the  phenomena  of  dreams,  in  which  only  a  part  of  the  mental 
faculties  are  at  rest  or  asleep,  while  the  others  are  awake,  and,  it  is  pre- 
sumed, are  exercised  through  the  medium  of  the  parts  of  the  brain 
appropriated  to  them. 

Unconscious  Cerebration. — In  connection  with  the  above,  some 
remarkable  pheuomena  should  be  mentioned  which  have  been  described 
as  depending  on  an  unconscious  action  of  the  brain. 

It  must  be  within  the  experience  of  every  one  to  have  tried  to  recol- 
lect some  particular  name  or  occurrence:  and  after  trying  in  vain  for  some 
time  the  attempt  is  given  up  and  quite  forgotten  amid  other  occupations, 
when  suddenly,  hours  or  even  a  day  or  two  afterward,  the  desired  name 
or  occurrence  unexpectedly  flashes  across  the  mind.  Such  occurrences 
are  supposed  by  many  to  be  due  to  the  requisite  cerebral  processes  going 
on  unconsciously,  and,  when  the  result  is  reached,  to  our  all  at  once  be- 
coming conscious  of  it. 

That  unconscious  cerebration  may  sometimes  occur,  is  likely  enough; 
and  it  is  paralleled  by  the  unconscious  walking  of  a  somnambulist.  But 
many  cases  of  so-called  unconscious  cerebration  are  better  explained  by 
the  supposition  that  some  missing  link  in  the  chain  of  reasoning  cannot 
at  the  moment  be  found;  but  is  afterward,  by  some  chance  combination 
of  events,  suggested,  and  thus  the  mental  process  is  at  once,  with  the  mem- 
ory of  what  has  gone  before,  completed. 

Again,  in  the  vain  endeavor  to  solve  a  difficult  or  it  may  be  an  easy 
problem,  the  reasoner  is  frequently  in  the  condition  of  a  man  whose 
wearied  muscles  could  never,  before  they  have  rested,  overcome  some 
obstacles.  In  both  cases, — of  brain  and  muscle,  after  renewal  of  their 
textures  by  rest,  the  task  is  performed  so  rapidly  as  to  seem  instantaneous. 

Aphasia. — From  the  apparently  greater  frequency  of  interference 
with  the  faculty  of  speech  in  disease  of  the  left  tlian  of  the  rigid  half  of 
the  cerebrum,  it  has  been  thought  that  tlie  nerve-centre  for  language,  in- 
cluding in  this  term  all  articulate  expression  of  ideas,  is  situated  in  the 
left  cerebral  hemisphere.  A  large  number  of  cases  are  on  record  in 
wiiich  aphasia,  or  the  loss  of  power  of  expressing  ideas  in  words,  has  been 
associated  with  disease  of  the  posterior  part  of  the  lower  or  third  frontal 
convohition  on  the  left  side.  Tliis  condition  is  usually  associated  with 
paralysis  of  tlu^  riglit  side  (right  liemiplegia).   Tlie  only  conclusion,  liow- 


THE  NEEVOUS  SYSTEM. 


131 


ever,  which  can  be  drawn  from  this,  is,  that  the  integrity  of  this  par- 
ticular convolution  is  essential  to  the  faculty  of  speech;  we  cannot  con- 
clude that  it  is  necessarily  the  centre  for  language.  It  may  be  only  one 
link  in  the  complete  chain  of  nervous  connections  necessary  for  the  trans- 
lation of  an  idea  into  articulate  expression. 

It  seems  highly  probable  that  the  corresponding  right  convolutions 
can  take  on  the  same  functions  as  the  left;  and  it  is  in  this  way  that  we 
can  explain  those  cases  in  which  recovery  of  speech  takes  place,  though 
the  left  frontal  convolution  still  remains  diseased. 

Pineal  and  Pituitaky  Bodies. 

Nothing  is  known  of  the  function  of  the  pineal  and  pituitary  bodies. 
They  have  been,  indeed,  supposed  by  some  to  be  rather  ductless  glands 
than  nervous  organs  (p.  10,  Vol.  II.). 

Experimental  Localizations. — Attempts  have  been  made  to  localize 
cerebral  functions  by  means  of  experiments  on  the  lower  animals.  It  had 
long  been  well  known  that  the  cerebral  hemispheres  could  not  be  excited 
by  mechanical,  chemical,  or  thermal  stimuli,  but  Pritsch  and  Hitzig 
were  the  first  to  show  that  they  are  amenable  to  electric  irritation.  They 
employed  a  weak  constant  current  in  their  experiments,  applying  a  pair 
of  fine  electrodes  not  more  than  in.  apart  to  different  parts  of  the 
cerebral  cortex.  The  results  thus  obtained  have  been  confirmed  and 
extended  by  Perrier. 

The  following  are  the  fundamental  phenomena  observed  in  all  these 
cases: 

(1.)  Excitation  of  the  same  spot  is  always  followed  by  the  same  move- 
ment in  the  same  animal.  (2.)  The  area  of  excitability  for  any  given 
movement  is  extremely  small,  and  admits  of  very  accurate  definition. 
(3.)  In  different  animals  excitations  of  anatomically  corresponding  spots 
produce  similar  or  corresponding  results  (Burden- Sanderson). 

The  various  definite  movements  resulting  from  the  electric  stimulation 
of  circumscribed  areas  of  the  cerebral  cortex,  are  enumerated  in  the 
description  of  the  accompanying  figures  of  the  dog  and  monkey^s  brain. 

In  the  case  of  the  dog,  the  results  obtained  are  summed  up  as  follows, 
by  Hitzig. 

,         (a.)  One  portion  (anterior)  of  the  convexity  of  the  cerebrum  is  motor; 

I  another  portion  (posterior)  is  non  motor.  (I. )  Electric  stimulation  of  the 
motor  portion  produces  co-ordinated  muscular  contraction  on  the  opposite 
side  of  the  body,  (c.)  With  very  weak  currents,  the  contractions  pro- 
duced are  distinctly  limited  to  particular  groups  of  muscles;  with 
stronger  currents  the  stimulus  is  communicated  to  other  muscles  of  the 


132  HAND-BOOK  OF  PHYSIOLOGY. 

same  or  neighboring  parts,  (d.)  The  portions  of  the  brain  intervening 
between  these  motor  centres  are  inexcitable  by  similar  means. 

With  regard  to  the  facts  above  mentioned,  all  experimenters  are 
agreed,  but  there  is  still  considerable  diversity  of  opinion  as  to  their  ex- 
planation. 


Figs.  341  and  342.— Brain  of  dog,  viewed  from  above  and  in  profile.  F,  frontal  fissure,  sometimes 
termed  crucial  sulcus,  corresponding:  to  the  fissure  of  Rolando  ui  man;  ^9,  fissure  of  Sylvius,  around 
which  the  fovn-  lonf^itudinal  convolutions  are  concentrically-  arran^rcd:  1.  flexion  of  head  on  the  neck, 
in  the  median  line;  2,  flexion  of  head  on  the  nc>ck,  with  rotation  toward  the  side  of  the  stinuilns;  3,4, 
flexion  and  extension  of  anterior  lind);  .'j,  G,  flexion  and  extension  of  posterior  limb;  7,  8,  i),  contrac- 
tion of  orbicularis  oculi,  and  the  facial  muscles  in  general.  The  unshaded  pai't  is  that  exposed  by 
opening  the  skull.  (Dalton.) 

It  is  evident  that  the  spots  marked  out  on  the  cortex  are  not  strictly 
speaking  motor  rodres,  for  they  can  be  removed  entirely  without  destroy- 
ing the  power  of  voluntary  motion. 

Burdon-Sanderson  lias  shown  that  electric  stimulation  of  different 


THE  NERVOUS  SYSTEM. 


133 


points  in  a  horizontal  section,  tlirongh  the  deeper  parts  of  the  hemi- 
spheres, produces  the  same  effects  as  stimulation  of  the  so-called  "centres" 
in  the  grey  matter  overlying  them:  while  the  same  results  follow  electric 
stimulation  of  different  points  of  the  corpus  striatum. 


Fig.  344. 

Figs.  s^-B  and  344. — Diagrams  of  monkey's  brain  to  show  the  effects  of  electric  stimulation  of  cer- 
tain spots.  1,  inovement  of  hind  foot;  2,  chiefly  adduction  of  foot;  3,  movements  of  hind  foot  and 
tail;  4,  of  latissimus  dorsi;  5,  extension  fom^ard  of  arm;  a,  6,  c,  d,  movements  of  hand  and  wrist;  6, 
supination  and  flexion  of  forearm;  7,  elevation  of  upper  hp;  8,  conjoint  action  of  elevation  of  upper 
lip  and  depression  of  lower;  9,  opening  of  mouth  and  protrusion  of  tongue;  10,  retraction  of  tongue; 
11,  action  of  platysma;  12,  elevation  of  eyebrows  and  eyehds,  dilatation  of  pupils,  and  turning  head 
to  opposite  side;  13,  eyes  directed  to  opposite  side  and  upward,  with  usually  contraction  of  the 
pupils;  13',  similar  action,  but  eyes  usually  directed  downward;  14,  retraction  of  opposite  ear,  head 
turns  to  the  opposite  side,  the  eyes  widely  opened  and  pupils  dilated;  15,  stimulation  of  this  region, 
which  corresponds  to  the  tip  of  the  uncinate  convolution,  causes  torsion  of  the  Up  and  nostril  of  the 
same  side.  (Ferrier.) 

In  applying  the  facts  ascertained  by  these  experiments  to  elucidate 
the  physiology  of  the  human  brain,  we  must  remember  that  the  method 
of  electric  stimulation  is  an  artificial  one,  differing  widely  from  the  ordi- 
nary stimuli  to  which  the  brain  is  subject  during  life. 


134 


HAND-BOOK  OF  PHYSIOLOGY. 


Functions  of  other  Parts  of  the  Brain. — Of  the  physiology  of  the 
other  parts  of  the  brain,  little  or  nothing  can  be  said. 

Of  the  offices  of  the  corpus  callosum,  or  great  transverse  and  oblique 
commissure  of  the  brain,  nothing  positive  is  known.  But  instances  in 
which  it  was  absent,  or  very  deficient,  either  without  any  evident  mental 
defect,  or  with  only  such  as  might  be  ascribed  to  coincident  affections  of 
other  parts,  make  it  probable  that  the  office  which  is  commonly  assigned 


Fig.  345.— View  of  the  corpus  callosum  from  above,  i^.— The  upper  surface  of  the  corpus  cal- 
losum has  been  fuUy  exposed  by  separating  the  cerebral  nemispheres  and  throwing  them  to  the  side; 
the  gyrus  fornicatus  has  been  detached,  and  the  transverse  fibres  of  the  corpus  callosum  traced  for 
some  distance  into  the  cerebral  medullary  substance.  1,  the  upper  surface  of  the  corpus  callosum; 
2,  median  furrow  or  raphe ;  3,  longitudinal  striae  bounding  the  furrow ;  4,  swelling  formed  by  the 
transverse  bands  as  they  pass  into  the  cerebrum;  5,  anterior  extremity  or  knee  of  the  corpus  cal- 
losum; G,  posterior  extremity;.  7,  anterior,  and  8,  posterior  part  of  the  mass  of  fibres  proceeding 
from  the  corpus  callosum;  9,  margin  of  the  swelling;  10,  anterior  part  of  the  convolution  of  the  cor- 

f)us  callosum;  11,  hem  or  band  of  union  of  this  convolution;  12,  internal  convolutions  of  the  parietal 
obe;  13,  upper  surface  of  the  cerebellum.   (Sappey  after  Foville.) 


to  it,  of  enabling  the  two  sides  of  the  brain  to  act  in  concord,  is  exercised 
only  in  the  highest  acts  of  which  the  mind  is  capable.  And  this  vicAV  is 
confirmed  by  the  very  late  period  of  its  development,  and  by  its  very  rudi- 
mentary condition  (Flower)  in  all  but  the  placental  Mammalia. 

To  the  fornix  and  other  commissures  no  special  function  can  be 
assigned;  but  it  is  a  rejisoiuiblc  liypothesis  that  they  connect  the  action 
of  the  parts  between  which  they  arc  severally  placed. 


THE  ^lEKVOUS  SYSTEM. 


135 


Sleep. 

All  parts  of  the  body  which  are  the  seat  of  active  change  require 
periods  of  rest.  The  alternation  of  work  and  rest  is  a  necessary  condi- 
tion of  their  maintenance  and  of  the  healthy  performance  of  their  func- 
tions. These  alternating  periods,  however,  differ  much  in  duration  in 
different  cases;  but,  for  any  individual  instance,  they  preserve  a  general 
and  rather  close  uniformity.  Thus,  as  before  mentioned,  the  periods  of 
rest  and  work,  in  the  case  of  the  heart,  occupy,  each  of  them,  about  half 
a  second;  in  the  case  of  the  ordinary  respiratory  muscles  the  periods  are 
about  four  or  five  times  as  long.  In  many  cases,  again  (as  of  the  volun- 
tary muscles  during  violent  exercise),  while  the  periods  during  active 
exertion  alternate  very  frequently,  yet  the  expenditure  goes  far  ahead  of 
the  repair,  and,  to  compensate  for  this,  an  after  repose  of  some  hours 
becomes  necessary;  the  rhythm  being  less  perfect  as  to  time,  than  in  the 
case  of  the  muscles  concerned  in  circulation  and  respiration. 

Obviously,  it  would  be  impossible  that,  in  the  case  of  the  Brain,  there 
should  be  short  periods  of  activity  and  repose,  or  in  other  words,  of  con- 
sciousness and  unconsciousness.  The  repose  must  occur  at  long  inter- 
vals; and  it  must  therefore  be  proportionately  long.  Hence  the  necessity 
for  that  condition  which  we  call  Sleep;  a  condition  which,  seeming  at  first 
sight  exceptional,  is  only  an  unusually  perfect  example  of  what  occurs,  at 
varying  intervals,  in  every  actively  working  portion  of  our  bodies. 

A  temporary  abrogation  of  the  functions  of  the  cerebrum  imitating 
sleep,  may  occur,  in  the  case  of  injury  or  disease,  as  the  consequence  of 
two  apparently  widely  different  conditions.  Insensibility  is  equally  pro- 
duced by  a  deficient  and  an  excessive  quantity  of  blood  within  the  cranium, 
(coma);  but  it  was  once  supposed  that  the  latter  offered  the  truest  anal- 
ogy to  the  normal  condition  of  the  brain  in  sleep,  and  in  the  absence  of 
any  proof  to  the  contrary,  the  brain  was  said  to  be  during  sleep  con- 
gested. Direct  experimental  enquiry  has  led,  however,  to  the  opposite 
conclusion. 

By  exposing,  at  a  circumscribed  spot,  the  surface  of  the  brain  of 
living  animals,  and  protecting  the  exposed  part  by  a  watch-glass,  Dur- 
ham was  able  to  prove  that  the  brain  becomes  visibly  paler  (anaemic) 
during  sleep;  and  the  anaemia  of  the  optic  disc  during  sleep,  observed  by 
Hughlings  Jackson,  may  be  taken  as  a  strong  confirmation,  by  analogy, 
of  the  same  fact. 

A  very  little  consideration  will  show  that  these  experimental  results 
correspond  exactly  with  what  might  have  been  foretold  from  the  analogy 
of  other  physiological  conditions.  Blood  is  supplied  to  the  brain  for  two 
partly  distinct  purposes.  (1.)  It  is  supplied  for  mere  nutrition's  sake. 
(2.)  It  is  necessary  for  bringing  supplies  of  potential  or  active  energy. 


136 


HAND-BOOK  OF  PHYSIOLOGY. 


(i.e.,  combustible  matter  or  heixt)  wliicli  may  be  transformed  by  the  cere- 
bral corpuscles  into  the  various  manifestations  of  nerve-force.  During 
sleep,  blood  is  requisite  for  only  the  first  of  these  purposes:  audits  supply 
in  greater  quantity  would  be  not  only  useless,  but,  by  supplying  an  ex- 
citement to  work,  when  rest  is  needed,  would  be  positi^'ely  harmful.  In 
this  respect  the  vai*ying  circulation  of  blood  in  the  brain  exactly  resem- 
bles that  which  occurs  in  all  other  energy  transforming  parts  of  the  body; 
e.g.,  glands  or  muscles. 

At  the  same  time,  it  is  necessary  to  remember  that  the  normal  anremia 
of  the  brain  which  accompanies  sleep  is  probably  a  result  and  not  a  cause 
of  the  quiescence  of  the  cerebral  functions.  What  the  immediate  cause 
of  this  periodical  partial  abrogation  of  function  is,  however,  we  do  not 
know. 

Somnambulism  and  Dreams. — What  we  term  sleep  occurs  often  in 
very  dilferent  degrees  in  difterent  parts  of  the  nervous  system;  and  in 
some  parts  the  expression  cannot  be  used  in  the  ordinary  sense. 

The  phenomena  of  dreams  and  som)iambulism  are  examples  of  differ- 
ing degrees  of  sleep  in  different  parts  of  the  cerebro-spinal  nervous  sys- 
tem. In  the  former  case  the  cerebrum  is  still  partially  active:  but  the 
mind-products  of  its  action  are  no  longer  corrected  by  the  reception,  on 
the  part  of  the  sleeping  se?isorium,  of  impressions  of  objects  belonging 
to  the  outer  world;  neither  can  the  cerebrum,  in  this  half -awake  con- 
dition, act  on  the  centres  of  reflex  action  of  the  voluntary  muscles,  so  as 
to  cause  the  latter  to  contract — a  fact  within  the  painful  experience  of 
all  who  have  sufl'ered  from  nightmare. 

In  somnambulism  the  cerebrum  is  capable  of  exciting  that  train  of 
reflex  nervous  action  which  is  necessary  for  progression,  while  the  nerve- 
centre  of  muscular  sense  (in  the  cerebellum?)  is,  presumably,  fully 
awake;  but  the  sensorium  is  still  asleep,  and  impressions  made  on  it  are 
not  sufficiently  felt  to  rouse  the  cerebrum  to  a  comparison  of  the  differ- 
ence between  mere  ideas  or  memories  and  sensations  derived  from  external 
objects. 

Physiology  of  the  Craxial  Xeeves. 

The  cranial  nerves  are  commonly  enumerated  as  nine  pairs;  but  the 
number  is  in  reality  twelve,  the  seventh  nerve  consisting  as  it  does,  of 
two  nerves,  and  the  eighth  of  tlu-ee.  All  arise  (superficial  origin'i  from 
the  base  of  the  encephalon,  in  a  double  series  which  extends  from  the 
under  surface  of  the  anterior  cerebral  lobes  to  the  lower  end  of  the 
medulla  oblongata.  Traced  into  the  substance  of  the  bmin  and  medulla, 
the  roots  of  the  nerves  are  found  connected  with  various  masses  of  grey 
matter,  which  ai'e  all  connected  one  with  another,  and  with  the  cerebral 
luMuisplieres. 


THE  NERVOUS  SYSTEM. 


137 


The  roots  of  the  olfactory  tracts  are  connected  deeply  with  the  cortex 
of  the  anterior  cerebral  hemisphere,  and  probably  with  the  corpora  striata 
also.  The  optic  nerves  can  be  traced  into  the  optic  thalami,  corpora 
qnadrigemina,  and  corpora  geniculata.  The  third  and  fourth  nerves  arise 
from  grey  matter  beneath  the  corpora  quadrigemina;  and  the  roots  of 
origin  of  the  remainder  of  the  cranial  nerves  can  be  traced  to  grey  matter 
in  the  medulla  oblongata  beneath  the  floor  of  the  fourth  ventricle,  and 
in  the  more  central  part  of  the  medulla,  around  its  central  canal,  as  low 
down  as  the  decussation  of  the  pyramids. 

According  to  their  several  functions,  the  cranial  nerves  may  be  thus 
arranged: — 

Nerves  of  special  sense     .    .   Olfactory,  optic,  auditory,  part  of  the 

glosso-pharyngeal,  and  of  the  lingual 
branch  of  the  fifth, 
of  common  sensation  .   The  greater  portion  of  the  fifth. 
"     of  motion    ....    Third,  fourth,  lesser  division  of  the  fifth, 

sixth,  facial,  and  hypoglossal. 
Mixed  nerves  Glossopharyngeal,  vagus,  and  spinal  ac- 
cessory. 

The  physiology  of  the  several  nerves  of  the  special  senses  will  be  con- 
sidered with  the  organs  of  those  senses. 

Thikd  Neeve. 

Functions. — The  third  nerve,  or  motor  ocuU,  supplies  the  levator 
palpebr©  superioris  muscle,  and,  of  the  muscles  of  the  eyeball,  all  but 
the  superior  oblique  or  trochlearis,  to  which  the  fourth  nerve  is  appropri- 
ated, and  the  rectus  externus  which  receives  the  sixth  nerve.  Through 
the  medium  of  the  ophthalmic  or  lenticular  ganglion,  of  which  it  forms 
what  is  called  the  short  root,  it  also  supplies  motor  filaments  to  the  iris 
and  ciliary  muscle. 

When  the  third  nerve  is  irritated  within  the  skull,  all  those  muscles 
to  which  it  is  distributed  are  convulsed.  When  it  paralyzed  or  divided 
the  following  effects  ensue:  (1),  the  upper  eyelid  can  be  no  longer  raised 
by  the  elevator  palpebrse,  but  droops  (ptosis)  and  remains  gently  closed 
over  the  eye,  under  the  unbalanced  influence  of  the  orbicularis  palpe- 
brarum, which  is  supplied  by  the  facial  nerve:  (2),  the  eye  is  turned  out- 
ward (external  strabismus)  by  the  unbalanced  action  of  the  rectus  ex- 
ternus, to  which  the  sixth  nerve  is  appropriated:  and  hence,  from  the 
irregularity  of  the  axes  of  the  eyes,  double-sight  is  often  experienced  when 
a  single  object  is  within  view  of  both  the  eyes:  (3),  the  eye  cannot  be 
moved  either  upward,  downward,  or  inward:  (4),  the  pupil  becomes 
dilated  (mydriasis),  and  insensible  to  light:  (5),  the  eye  cannot  "accom- 
modate" itself  for  vision  at  short  distances. 


138  HAND-BOOK  OF  PHYSIOLOGY. 

Contraction  and  Dilatation  of  the  Pupil. — The  relation  of  tlie 
third  nerve  to  the  iris  is  of  peculiar  interest.  In  ordinary  circumstances 
the  contraction  of  the  iris  is  a  reflex  action,  which  may  be  explained  as 
produced  by  the  stimulus  of  light  on  the  retina  being  conveyed  by  the 
optic  nerve  to  the  brain  (probably  to  the  corpora  quadrigemina),  and 
thence  reflected  through  the  third  nerve  to  the  iris.  Hence  the  iris  ceases 
to  act  when  either  the  optic  or  the  third  nerve  is  divided  or  destroyed, 
or  when  the  cor]Dora  quadrigemina  are  destroyed  or  much  compressed. 
But  when  the  optic  nerve  is  divided,  the  contraction  of  the  iris  may  be 
excited  by  irritating  that  portion  of  the  nerve  which  is  connected  with 
the  brain;  and  when  the  third  nerve  is  divided,  the  irritation  of  its  distal 
portion  will  still  excite  the  contraction  of  the  iris. 

The  contraction  of  the  iris  thus  shows  all  the  characters  of  a  reflex 
act,  and  in  ordinary  cases  requires  the  concurrent  action  of  the  optic 
nerve,  corpora  quadrigemina,  and  third  nerve;  and,  probably  also,  con- 
sidering the  peculiarities  of  its  perfect  mode  of  action,  of  the  ophthalmic 
ganglion.  But,  besides,  both  irides  will  contract  their  pupils  under  the 
reflected  stimulus  of  light  falling  only  on  one  retina  or  under  irritation 
of  one  optic  nerve.  Thus,  in  blindness  of  one  eye,  its  pupil  may  contract 
when  the  other  eye  is  exposed  to  a  stronger  light:  and  generally  the  con- 
traction of  each  of  the  pupils  appears  to  be  in  direct  proportion  to  the 
total  quantity  of  light  which  stimulates  either  one  or  both  retinae,  accord- 
ing as  one  or  both  eyes  are  open. 

The  iris  acts  also  in  association  with  certain  other  muscles  supplied  by  " 
the  third  nerve:  thus,  when  the  eye  is  directed  inward,  or  upward  and  in- 
ward, by  the  action  of  the  third  nerve  distributed  in  the  rectus  internus 
and  rectus  superior,  the  iris  contracts,  as  if  under  direct  voluntary  in- 
fluence. The  will  cannot,  however,  act  on  the  iris  alone  through  the 
third  nerve;  but  this  aptness  to  contract  in  association  with  the  other 
muscles  supplied  by  the  third,  may  be  sufficient  to  make  it  act  even  in 
total  blindness  and  insensibility  of  the  retina,  whenever  these  muscles 
are  contracted.  The  contraction  of  the  pupils,  when  the  eyes  are  moved 
inward,  as  in  looking  at  a  near  object,  has  probably  the  purpose  of  ex- 
cluding those  outermost  ra3^s  of  light  which  would  be  too  far  divergent  to 
be  refracted  to  a  clear  image  on  the  retina;  and  the  dilatation  in  looking 
straight  forward  as  in  looking  at  a  distant  object,  permits  the  admission 
of  the  largest  number  of  rays,  of  which  none  are  too  divergent  [to  be  so 
refracted.  (For  further  remarks  on  the  contraction  and  dilatation  of  the 
pupil,  see  pp.  205,  20G,  Vol.  II.) 

Fourth  Nerve. 

Functions. — The  fourth  nerve,  or  Ncrvns  trochlearis  or  jiafJicticus, 
is  exclusively  motor,  and  supplies  only  the  trochlearis  or  obliquus  siii)(M-ior 
nuisT'le  of  tlic  oyobnll. 


THE  NERVOUS  SYSTEM- 


139 


Fifth  or  Trigeminal  Nerve. 

Functions. — The  fifth  or  trigeminal  nerve  resembles,  as  already- 
stated,  the  spinal  nerves,  in  that  its  branches  are  derived  through  two 
roots;  namely,  the  larger  or  sensory,  in  connection  with  which  is  the  Gas- 
serian  ganglion,  and  the  smaller  or  motor  root  which  has  no  ganglion,  and 
which  passes  under  the  ganglion  of  the  sensory  root  to  join  the  third 
branch  or  division  which  issues  from  it.  The  first  and  second  divisions 
of  the  nerve,  which  arise  wholly  from  the  larger  root,  are  purely  sensory. 
The  third  division  being  joined,  as  before  said,  by  the  motor  root  of  the 
nerve,  is  of  course  both  motor  and  sensory. 

(a.)  Motor  Functions. — Through  branches  of  the  lesser  or  non- 
ganglionic  portion  of  the  fifth,  the  muscles  of  mastication,  namely,  the 
temporal,  masseter,  two  pterygoid,  anterior  part  of  the  digastric,  and 
mylo-hyoid,  derive  their  motor  nerves.  Filaments  are  also  supplied  to 
the  tensor  tympani  and  tensor  palati.  The  motor  function  of  these  - 
branches  is  proved  by  the  violent  contraction  of  all  the  muscles  of  masti- 
cation in  experimental  irritation  of  the  third  or  inferior  maxillary  division 
of  the  nerve;  by  paralysis  of  the  same  muscles,  when  it  is  divided  or 
disorganized,  or  from  any  reason  deprived  of  power;  and  by  the  retention 
of  the  power  of  these  muscles,  when  all  those  supplied  by  the  facial  nerve 
lose  their  power  through  paralysis  of  that  nerve.  The  last  instance  proves 
best,  that  though  the  buccinator  muscle  gives  passage  to,  and  receives 
some  filaments-  from,  a  buccal  branch  of  the  inferior  division  of  the  fifth 
nerve,  yet  it  derives  its  motor  power  from  the  facial,  for  it  is  paralyzed 
together  with  the  other  muscles  that  are  supplied  by  the  facial,  but 
retains  its  power  when  the  other  muscles  of  mastication  are  paralyzed. 
Whether,  however,  the  branch  of  the  fifth  nerve  which  is  supplied  to  the 
buccinator  muscle  is  entirely  sensory,  or  in  part  motor  also,  must  remain 
for  the  present  doubtful.  From  the  fact  that  this  muscle,  besides  its 
other  functions,  acts  in  concert  or  harmony  with  the  muscles  of  mastica- 
tion, in  keeping  the  food  between  the  teeth,  it  might  be  supposed  from 
analogy,  that  it  would  have  a  motor  branch  from  the  same  nerve  that  sup- 
plies them.  There  can  be  no  doubt,  however,  that  the  so-called  buccal 
branch  of  the  fifth  is,  in  the  main,  sensory;  although  it  is  not  quite  cer- 
tain that  it  does  not  give  a  few  motor  filaments  to  the  buccinator  muscle. 

(b.)  Sensory  Functions. — Through  the  branches  of  the  greater  or 
ganglionic  portion  of  the  fifth  nerve,  all  the  anterior  and  antero-lateral 
parts  of  the  face  and  head,  with  the  exception  of  the  skin  of  the  parotid 
region  (which  derives  branches  from  the  cervical  spinal  nerves),  acquire 
common  sensibility;  and  among  these  parts  may  be  included  the  organs 
of  special  sense,  from  which  common  sensations  are  conveyed  through  the 
fifth  nerve,  and  their  special  sensations  through  their  several  nerves  of 


140 


HAND-BOOK  OF  PHYSIOLOGY. 


special  sense.  The  muscles,  also,  of  the  face  and  lower  jaw  acquire 
muscular  sensibility,  through  the  filaments  of  the  ganglionic  portion  of 
the  fifth  nerve  distributed  to  them  with  their  proper  motor  nerves.  The 
sensory  function  of  the  branches  of  the  greater  division  of  the  fifth 
nerve  is  proved,  by  all  the  usual  evidences,  such  as  their  distribution  in 
parts  that  are  sensitive  and  not  capable  of  muscular  contraction,  the  ex- 
ceeding sensibility  of  some  of  these  parts,  their  loss  of  sensation  when 


Fig.  346.— General  plan  of  the  branches  of  the  fifth  pair.  1-3.— 1,  lesser  root  of  the  fifth  pair;  2, 
greater  root  passing  forward  into  the  Gasserian  ganglion;  3,  placed  on  the  bone  above  the  ophthal- 
mic nerve,  which  is  seen  dividing  into  the  supra-orbital,  lachrymal,  and  nasal  branches,  the  latter 
connected  with  the  ophthalmic  ganglion;  4,  placed  on  the  bone  close  to  the  foramen  rotundum,  marks 
the  superior  maxillary  division,  which  is  connected  below  with  the  spheno-palatine  ganglion,  and 
passes  forward  to  the  infra-orbital  foramen ;  5,  placed  on  the  bone  over  the  foramen  ovale,  marks 
the  inferior  maxillary  nerve,  giving  off  the  anterior  auricular  and  muscular  branches,  and  continued 
by  the  inferior  dental  to  the  lower  jaw,  and  by  the  gustator.y  to  the  tongue;  o,  the  submaxillary 
gland,  the  submaxillary  ganglion  placed  above  it  in  connection  with  the  gustatory  nerve;  6,  the 
chorda  tympani;  7,  the  facial  nerve  issuing  from  the  stylo-mast  old  foramen.   (Charles  BeU.) 

the  nerve  is  paralyzed  or  divided,  the  pain  without  convulsions  produced 
by  morbid  or  experimental  irritation  of  the  trunk  or  branches  of  the  nerve, 
and  the  analogy  of  this  portion  of  the  fifth  to  the  posterior  root  of  the 
spinal  nerve. 

Other  Functions. — In  relation  io  miisniJar  movements,  the  branches 
of  the  greater  or  ganglionic  portion  of  the  fifth  nerve  exercise  a  manifold 
influence  on  the  movements  of  the  muscles  of  the  head  and  face,  and 
other  parts  in  which  thoy  are  distributed.  They  do  so,  in  the  first  jilace 
{a),  by  providing  the  muscles  themselves  with  that  sensibility  without 
which  the  mind,  being  unconscious  of  ilieir  j^osition  and  state,  cannot 


THE  NERVOUS  SYSTEM. 


141 


voluntarily  exercise  them.  It  is,  probably,  for  conferring  this  sensibility 
on  the  muscles,  that  the  branches  of  the  fifth  nerve  communicate  so  fre- 
quently with  those  of  the  facial  and  hypoglossal,  and  the  nerves  of  the 
muscles  of  the  eye;  and  it  is  because  of  the  loss  of  this  sensibility  that 
when  the  fifth  nerve  is  divided,  animals  are  always  slow  and  awkward  in 
*  the  movement  of  the  muscles  of  the  face  and  head,  or  hold  them  still,  or 
guide  their  movements  by  the  sight  of  the  objects  toward  which  they 
wish  to  move. 

Again,  the  fifth  nerve  has  an  indirect  influence  on  the  muscular  move- 
ments by  (b)  conveying  sensations  of  the  state  and  position  of  the  skin 
and  other  parts:  which  the  mind  perceiving,  is  enabled  to  determine 
appropriate  acts.  Thus,  when  the  fifth  nerve  or  its  infra-orbital  branch 
is  divided,  the  movements  of  the  lips  in  feeding  may  cease,  or  be  imper- 
fect. Bell  supposed  that  the  motion  of  the  upper  lip  in  grasping  food 
depended  directly  on  the  infra- orbital  nerve;  for  he  found  that,  after  he 
had  divided  that  nerve  on  both  sides  in  an  ass,  it  no  longer  seized  the 
food  with  its  lips,  but  merely  pressed  them  against  the  ground,  and  used 
the  tongue  for  the  prehension  of  the  food.  Mayo  corrected  this  error. 
He  found,  indeed,  that  after  the  infra-orbital  nerve  had  been  divided,  the 
animal  did  not  seize  its  food  with  the  lip,  and  could  not  use  it  well  during 
mastication,  but  that  it  could  open  the  lips.  He,  therefore,  justly  attrib- 
uted the  phenomena  in  Bellas  experiments  to  the  loss  of  sensation  in  the 
lips;  the  animal  not  being  able  to  feel  the  food,  and,  therefore,  although 
it  had  the  power  to  seize  it,  not  knowing  how  or  where  to  use  that  power. 

The  fifth  nerve  has  also  (c),  an  intimate  connection  with  muscular 
movements  through  the  many  reflex  acts  of  muscles  of  which  it  is  the 
necessary  excitant.  Hence,  when  it  is  divided  and  can  no  longer  convey 
impressions  to  the  nervous  centres  to  be  thence  reflected,  the  irritation  of 
the  conjunctiva  produces  no  closure  of  the  eye,  the  mechanical  irritation 
of  the  nose  excites  no  sneezing. 

Through  its  ciliary  branches  and  the  branch  which  forms  the  long 
root  of  the  ciliary  or  ophthalmic  ganglion,  it  exercises  also  (d),  some  in- 
fluence on  the  movements  of  the  iris. 

When  the  trunk  of  the  ophthalmic  portion  is  divided,  the  pupil  be- 
comes, according  to  Valentin,  contracted  in  men  and  rabbits,  and  dilated 
in  cats  and  dogs;  but  in  all  cases,  becomes  immovable  even  under  all  the 
varieties  of  the  stimulus  of  light.  How  the  fifth  nerve  thus  affects  the 
iris  is  unexplained;  the  same  effects  are  produced  by  destruction  of  the 
superior  cervical  ganglion  of  the  sympathetic,  so  that,  possibly,  they  are 
due  to  the  injury  of  those  filaments  of  the  sympathetic  which,  after  join- 
ing the  trunk  of  the  fifth,  at  and  beyond  the  Gasserian  ganglion,  proceed 
with  the  branches  of  its  ophthalmic  division  to  the  iris;  or,  as  E.  Hall 
ingeniously  suggests,  the  influence  of  the  fifth  nerve  on  the  movements 
of  the  iris  may  be  ascribed  to  the  affection  of  vision  in  consequence  of 


142 


HAND-BOOK  OF  PHYSIOLOGY. 


the  disturbed  circulation  or  nutrition  in  the  retina^  when  the  normal  in- 
fluence of  the  fifth  nerve  and  ciliary  ganglion  is  disturbed.  In  such  dis- 
turbance^ increased  circulation  making  the  retina  more  irritable  might 
induce  extreme  contraction  of  the  iris;  or  under  moderate  stimulus  of 
lights  producing  partial  blindness,  might  induce  dilatation:  but  it  does  not 
appear  wh}^  if  this  be  the  true  explanation,  the  iris  should  in  either  case 
be  immovable  and  unaffected  by  the  various  degrees  of  light. 

Tropliic  influence. — Furthermore,  the  morbid  effects  which  division  of 
the  fiftli  nerve  produces  in  the  organs  of  special  sense,  make  it  probable 
that,  in  the  normal  state,  the  fiftli  nerve  exercises  some  trophic  influence 
on  all  these  organs;  although,  in  part,  the  effect  of  the  section  of  the 
nerve  is  only  indirectly  destructive  by  abolishing  sensation,  and  therefore 
the  natural  safeguard  which  leads  to  the  protection  of  parts  from  ex- 
ternal injury.  Thus,  after  such  division,  within  a  period  varying  from 
twenty-four  hours  to  a  week,  the  cornea  begins  to  be  opaque;  then  it 
grows  completely  white;  a  low  destructive  inflammatory  process  ensues  in 
the  conjunctiva,  sclerotica,  and  interior  parts  of  the  eye;  and  within  one 
or  a  few  weeks,  the  whole  eye  may  be  quite  disorganized,  and  the  cornea 
may  slough  or  be  penetrated  by  a  large  ulcer.  The  sense  of  smell  (and  not 
merely  that  of  mechanical  irritation  of  the  nose),  may  be  at  the  same 
time  lost  or  gravely  impaired;  so  may  the  hearing,  and  commonly,  when- 
ever the  fifth  nerve  is  paralyzed,  the  tongue  loses  the  sense  of  taste  in  its 
anterior  and  lateral  j)arts,  i.e.,  in  the  portion  in  which  the  lingual  or 
gustatory  branch  of  the  inferior  maxillary  division  of  the  fifth  is  dis- 
tributed. 

In  relation  to  Taste. — The  loss  of  the  sense  of  taste  is  no  doubt  due  {a) 
to  the  lingual  branch  of  the  fifth  nerve  being  a  nerve  of  special  sense; 
partly,  also,  it  is  due  (b),  to  the  fact  that  this  branch  supplies,  in  the 
anterior  and  lateral  parts  of  the  tongue,  a  necessary  condition  for  the 
proper  nutrition  of  that  part;  while  (c),  it  forms  also  one  chief  link  in 
the  nervous  circle  for  reflex  action,  in  the  secretion  of  saliva  (p.  231,  Vol. 
I.).  But,  deferring  this  question  until  the  glosso-pharyngeal  nerve  is  to 
be  considered,  it  may  be  observed  that  in  some  brief  time  after  complete 
l^aralysis  or  division  of  the  fifth  nerve,  the  power  of  all  the  organs  of  the 
special  senses  may  be  lost;  they  may  lose  not  merely  their  sensibility  to 
common  impressions,  for  which  they  all  depend  directly  on  the  fifth 
nerve,  but  also  their  sensbility  to  their  several  peculiar  impressions  for 
tlie  reception  and  conduction  of  Avhich  they  are  purposely  constructed 
and  supplied  with  special  nerves  besides  the  fifth.  Tlie  facts  observed  in 
these  cases  can,  perhaps,  be  only  explained  by  the  influence  wliich  the 
fiftli  nerve  exercises  on  the  nutritive  processes  in  tlie  organs  of  the  special 
senses.  It  is  not  unreasonable  to  believe,  that,  in  paralysis  of  tlie  fifth 
nerve,  their  tissues  may  be  the  seats  of  such  changes  as  are  seen  in  tlu^ 
laxity,  tlic  vascular  congestion,  aMlema,  and  oilier  atVectious  of  the  skin 


THE  NERVOUS  SYSTEM. 


143 


of  the  face  and  other  tegumentary  parts  which  also  accompany  the  paral- 
ysis; and  that  these  changes,  which  may  appear  unimportant  when  they 
affect  external  parts,  are  sufficient  to  destroy  that  refinement  of  structure 
by  which  the  organs  of  the  special  senses  are  adapted  to  their  functions. 

That  complete  paralysis  of  the  fifth  nerve  may  be  unaccompanied,  at 
least  for  a  considerable  period,  by  injury  to  the  organs  of  special  sense, 
with  the  exception  of  that  portion  of  the  tongue  which  is  supplied  by  its 
gustatory  branch,  is  well  illustrated  by  a  valuable  case  recorded  by 
Althaus. 

According  to  Magendie  and  Longet,  destruction  of  the  eye  ensues 
more  quickly  after  division  of  the  trunk  of  the  fifth  beyond  the  Gras- 
serian  ganglion,  or  after  division  of  the  ophthalmic  branch,  than  after 
division  of  the  roots  of  the  fifth  between  the  brain  and  the  ganglion. 
Hence  it  would  appear  as  if  the  infiuence  on  nutrition  were  conveyed 
in  part  through  the  filaments  of  the  sympathetic,  which  joins  the 
branches  of  the  fifth  nerve  at  and  beyond  the  Grasserian  ganglion. 

The  existence  of  ganglia  of  the  sympathetic  in  connection  with  all 
the  principal  divisions  of  the  fifth  nerve  where  it  gives  off  those  branches 
which  supply  the  organs  of  special  sense — for  example,  the  connection  of 
the  ophthalmic  ganglion  with  the  ophthalmic  nerve  at  the  origin  of  the 
ciliary  nerves;  of  the  spheno-palatine  ganglion  with  the  superior  maxil- 
lary division,  where  it  gives  its  branches  to  the  nose  and  the  palate;  of 
the  otic  ganglion  with  the  inferior  maxillary  near  the  giving  off  of  fila- 
ments to  the  internal  ear;  and  of  the  sub-maxillary  ganglion  with  the 
lingual  branch  of  the  fifth — all  these  connections  suggest  that  a  peculiar 
and  probably  conjoint  influence  of  the  sympathetic  and  fifth  nerves  is 
exercised  in  the  nutrition  of  the  organs  of  the  special  senses;  and  the 
results  of  experiment  and  disease  confirm  this,  by  showing  that  the 
nutrition  of  the  organs  may  be  impaired  in  consequence  of  impairment  of 
the  power  of  either  of  the  nerves. 

In  relation  to  Sight. — A  possible  but  doubtful  connection  between  the 
fifth  nerve  and  the  sense  of  sight,  has  been  thought  to  be  shown  in  cases 
in  which  blows  or  other  injuries  implicating  the  frontal  nerve  as  it  passes 
over  the  brow,  are  followed  by  total  blindness  in  the  corresponding  eye. 
In  some  cases  the  blindness  occurs  at  once,  probably  from  concussion  of 
the  retina;  but  in  others  it  is  very  slowly  progressive,  as  if  from  defective 
nutrition  of  the  retina,  and  may  be  accompanied  with  inflammatory  dis- 
organization, like  that  previously  referred  to  (p.  141,  Vol.  II.).  The  con- 
nection of  the  fifth  nerve  with  the  result  must,  however,  be  considered 
very  doubtful. 

Sixth  Nerve. 

Functions. — The  sixth  nerve,  Nervus  aMucens  or  ocularis  externus, 
IS  also,  like  the  fourth,  exclusively  motor,  and  supplies  only  the  rectus 
externus  muscle. 

The  rectus  externus  is  convulsed,  and  the  eye  is  turned  outward,  when 


144 


HAND-BOOK  OF  PHYSIOLOGY. 


the  sixth  nerve  is  irritated;  and  the  muscle  is  paralyzed  Avhen  the  nerve  is 
divided.  In  all  such  cases  of  paralysis,  the  eye  squints  inward,  and  cannot 
be  moved  outward. 

In  its  course  through  the  cavernous  sinus,  the  sixth  nerve  forms  larger 
communications  with  the  sympathetic  nerve  than  any  other  nerve 
within  the  cavity  of  the  skull  does.  But  the  import  of  these  communi- 
cations with  the  sympathetic,  and  the  subsequent  distribution  of  its  fila- 
ments after  joining  the  sixth  nerve,  are  quite  unknown. 

Setexth  oe  Facial  Xerye. 

Functions. — The  facial  ov  portio  dura  of  the  seYenth  pair  of  nerves, 
is  the  motor  nerve  of  all  the  muscles  of  the  face,  including  the  platysma, 
but  not  including  any  of  the  muscles  of  mastication  already  enumerated 
(p.  225,  Vol.  I.);  it  supplies,  also,  the  parotid  gland,  and  through  the 
connection  of  its  trunk  with  the  Vidian  nerve,  by  the  petrosal  nerves, 
some  of  the  muscles  of  the  soft  palate,  probably  the  levator  palati  and 
azygos  uvulae;  by  its  tympanic  branches  it  supplies  the  stapedius  and  laxator 
tympani,  and,  through  the  otic  ganglion,  the  tensor  tympani;  through 
the  chorda  ti/m^yani  it  sends  branches  to  the  submaxillary  gland  and  to 
the  lingualis  and  some  other  muscular  fibres  of  the  tongue;  and  by  branches 
given  off  before  it  comes  upon  the  face,  it  supplies  the  muscles  of  the  ex- 
ternal ear,  the  posterior  part  of  the  digastricus,  and  the  stylo- hyoideus. 

Besides  its  motoj'  influence,  the  facial  is  also,  by  means  of  the  fibres 
which  are  supplied  to  the  submaxillary  and  parotid  glands,  a  secretory 
nerve.  For,  through  the  last-named  branches,  impressions  may  be  con- 
veyed which  excite  increased  secretion  of  saliva  (p.  232,  Vol.  I.). 

Symptoms  of  Paralysis  of  Facial  Nerve. — When  the  facial  nerve 
is  divided,  or  in  any  other  way  paralyzed,  the  loss  of  power  in  the  muscles 
which  it  supplies,  while  proving  the  nature  and  extent  of  its  functions, 
displays  also  the  necessity  of  its  perfection  for  the  perfect  exercise  of  all 
the  organs  of  the  special  senses.  Thus,  in  paralysis  of  the  facial  nerve, 
the  orbicularis  palpebrarum  being  powerless,  the  eye  remains  open  through 
the  unbalanced  action  of  the  levator  palpebr^e;  and  the  conjunctiva,  thus 
continually  exposed  to  the  air  and  the  contact  of  dust,  is  liable  to  repeated 
inflammation,  which  may  end  in  thickening  and  opacity  of  both  its  own 
tissue  and  that  of  the  cornea.  These  changes,  however,  ensue  much 
more  slowly  than  those  which  follow  paralysis  of  the  fifth  nerve,  and  never 
bear  the  same  destructive  character. 

The  sense  of  liearing,  also,  is  impaired  in  many  cases  of  paralysis  of 
the  facial  nerve;  not  only  in  such  as  are  instances  of  simultaneous  disease 
in  the  auditory  nerves,  but  in  such  as  may  be  explained  by  the  loss  of 
1)0 wer  in  the  muscles  of  the  internal  ear.  The  sense  of  smell  is  commonly 
at  the  same  time  im})aire(]  tlirough  tlie  inability  to  draw  air  briskly  toAvard 


THE  NEEVOITS  SYSTEM. 


145 


the  upper  part  of  the  nasal  cavities  in  which  part  alone  the  olfactory  nerve 
is  distributed;  because,  to  draw  the  air  perfectly  in  this  direction,  the 
action  of  the  dilators  and  compressors  of  the  nostrils  should  be  perfect. 

Lastly,  the  sense  of  taste  is  impaired  or  may  be  wholly  lost  in  paralysis 
of  the  facial  nerve,  provided  the  source  of  the  paralysis  be  in  some  part 
of  the  nerve  between  its  origin  and  the  giving  off  of  the  chorda  tympani. 
This  result,  which  has  been  observed  in  many  instances  of  disease  of  the 
facial  nerve  in  man,  appears  explicable  by  the  influence  which,  through 
the  chorda  tympani,  it  exercises  on  the  movements  of  the  lingualis  and 
the  adjacent  muscular  fibres  of  the  tongue;  and  on  the  process  of  secre- 
tion of  saliva. 

Together  with  these  effects  of  paralysis  of  the  facial  nerve,  the  muscles 
of  the  face  being  all  powerless,  the  countenance  acquires  on  the  paralyzed 
side  a  characteristic,  vacant  look,  from  the  absence  of  all  expression:  the 
angle  of  the  mouth  is  lower,  and  the  paralyzed  half  of  the  mouth  looks 
longer  than  that  on  the  other  side;  the  eye  has  an  unmeaning  stare.  All 
these  peculiarities  increase,  the  longer  the  paralysis  lasts;  and  their  ap- 
pearance is  exaggerated  when  at  any  time  the  muscles  of  the  opposite 
side  of  the  face  are  made  active  in  any  expression,  or  in  any  of  their 
ordinary  functions.  In  an  attempt  to  blow  or  whistle,  one  side  of  the 
mouth  and  cheek  acts  properly,  but  the  other  side  is  motionless,  or  flaps 
loosely  at  the  impulse  of  the  expired  air;  so  in  trying  to  suck,  one  side 
only  of  the  mouth  acts;  in  feeding,  the  lips  and  cheek  are  powerless,  and 
food  lodges  between  the  cheek  and  gum. 

Glosso-Phartkgeal  Neeve. 

The  glosso-pharyngeal  nerves  (16,  Fig.  347),  in  the  enumeration  of  the 
cerebral  nerves  by  numbers  according  to  the  position  in  which  they  leave 
the  cranium,  are  considered  as  divisions  of  the  eighth  pair  of  nerves,  in 
which  term  are  included  with  them  the  pneumogastric  and  accessory 
nerves.  But  the  union  of  the  nerves  under  one  term  is  inconvenient, 
although  in  some  parts  the  glosso-pharyngeal  and  pneumogastric  are  so 
combined  in  their  distribution  that  it  is  impossible  to  separate  them  in 
either  their  anatomy  or  physiology. 

Distribution. — The  glosso-pharyngeal  nerve  gives  filaments  through 
its  tympanic  branch  (Jacobson's  nerve,)  to  the  fenestra  ovalis,  and  fenestra, 
rotunda,  and  the  Eustachian  tube;  also,  to  the  carotid  plexus,  and, 
through  the  petrosal  nerve,  to  the  spheno-palatine  ganglion.  After  com- 
municating, either  within  or  without  the  cranium,  with  the  pneumogas- 
tric, and  soon  after  it  leaves  the  cranium,  with  the  sympathetic,  digastric; 
branch  of  the  facial,  and  the  accessory  nerve,  the  glosso-pharyngeal  nerve^ 
parts  into  the  two  principal  divisions  indicated  by  its  name,  and  supplies; 
the  mucous  membrane  of  the  posterior  and  lateral  walls  of  the  upper  part 
Vol.  II.— 10. 


146 


HAND-BOOK  OF  PHYSIOLOGY. 


of  the  pharynx,  the  Eustachian  tube,  the  arches  of  the  palate,  the  tonsils 
and  their  mucous  membrane,  and  the  tongue  as  far  forward  as  the  foramen 
caecum  in  the  middle  line,  and  to  near  the  tip  at  the  sides  and  inferior 
part. 

Functions. — The  glosso-pharyngeal  nerve  contains  some  motor  fibres, 
together  with  those  of  common  sensation  and  the  sense  of  taste.  1.  The 
muscles  which  receive  filaments  from  the  glosso-pharyngeal  are  the  stylo- 
pharyngei,  palato-giossi,  and  constrictors  of  the  pharynx. 

Besides  being  (2)  a  nerve  of  common  sensation  in  the  parts  which  it 
supplies,  and  a  centripetal  nerve  through  which  impressions  are  conveyed 
to  be  reflected  to  the  adjacent  muscles,  the  glosso-pharyngeal  is  also  a 
nerve  of  special  sensation;  being  the  nerve  of  taste,  in  all  the  parts  of 
the  tongue  and  palate  to  which  it  is  distributed.  After  many  discussions, 
the  question.  Which  is  the  nerve  of  taste? — the  lingual  branch  of  the  fifth, 
or  the  glosso-pharyngeal? — may  be  most  probably  answered  by  stating 
that  they  are  both  nerves  of  this  special  function.  Eor  very  numerous 
experiments  and  cases  have  shown  that  when  the  trunk  of  the  fifth  nerve 
or  its  lingual  branch  is  23aralyzed  or  divided,  the  sense  of  taste  is  completely 
lost  in  the  superior  surface  of  the  anterior  and  lateral  parts  of  the  tongue. 
The  loss  is  instantaneous  after  division  of  the  nerve;  and,  therefore,  cannot 
be  ascribed  to  the  defective  nutrition  of  the  part,  though  to  this,  perhaps, 
may  be  ascribed  the  more  complete  and  general  loss  of  the  sense  of  taste 
when  the  whole  of  the  fifth  nerve  has  been  paralyzed. 

But,  on  the  other  hand,  while  the  loss  of  taste  in  the  part  of  the  tongue 
to  which  the  lingual  branch  of  the  fifth  nerve  is  distributed  proves  that  to 
be  a  gustatory  nerve,  the  fact  that  the  sense  of  taste  is  at  the  same  time 
retained  in  the  posterior  and  postero-lateral  parts  of  the  tongue,  and  in  the 
soft  palate  and  its  anterior  arch,  to  which  (and  to  some  parts  of  which 
exclusively)  the  glosso-pharyngeal  is  distributed,  proves  that  this  also 
must  be  a  nerve  of  taste. 

Pkeumogastric  oe  Vagus  Nerve. 

Distribution. — The  pneumogastric  nerve,  nerviis  vagus,  ox  par  vagum 
(1,  Fig.  347),  has,  of  all  the  cranial  and  spinal  nerves,  the  most  various 
distribution,  and  influences  the  most  various  functions,  either  through  its 
own  filaments,  or  those  which,  derived  from  other  nerves,  are  mingled  in 
its  branches.  The  parts  supplied  by  the  branches  of  the  vagus  nerve  are 
as  follows:  by  its  pharyngeal  branches,  which  enter  the  pharyngeal 
plexus,  a  large  portion  of  the  mucous  membrane,  and,  probably,  all  the 
muscles  of  the  Pharynx;  by  the  superior  laryngeal  nerve,  the  mucous  mem- 
brane of  the  under  surface  of  the  Epiglottis,  the  Glottis,  and  the  greater 
part  of  the  Larynx,  and  the  crico-thyroid  muscle;  by  the  inferior  laryn- 
geal nerve,  the  mucous  membrane  and  muscular  fibres  of  the  l^rachoa, 


THE  NERVOUS  SYSTEM. 


147 


the  lower  part  of  the  pharynx  and  larynx,  and  all  the  muscles  of  the  larynx 
except  the  crico- thyroid;  by  oesophageal  branches,  the  mucous  membrane 
and  muscular  coats  of  the  (Esophagus.    Moreover,  the  branches  of  the 


Fig.  347.— View  of  the  nerves  of  the  eighth  pair,  their  distribution  and  connections  on  the  left 
side.  2-5.— 1,  pneumogastric  nerve  in  the  neck;  2,  ganglion  of  its  trunk;  3,  its  union  with  the  spinal 
accessory;  4,  its  union  with  the  hypoglossal;  5,  pharyngeal  branch;  6,  superior  laryngeal  nerve;  7, 
external  laryngeal;  8,  laryngeal  plexus;  9,  inferior  or  recurrent  laryngeal;  10,  superior  cardiac 
branch;  11,  middle  cardiac;  12,  plexiform  part  of  the  nerve  in  the  thorax;  13,  posterior  pulmonary 
plexus;  14,  Ungual  or  gustatory  nerve  of  the  inferior  maxillary;  15,  hypoglossal,  passing  into  the 
muscles  of  the  tongue,  giving  its  thyroid-hyoid  branch,  and  uniting  with  twigs  of  the  lingual;  16, 
glosso-pharyngeal  nerve;  17,  spinal  accessory  nerve,  uniting  by  its  inner  branch  with  the  pneumo- 
gastric,  and  by  its  outer,  passing  into  the  sterno-mastoid  muscle;  18,  second  cervical  nerve;  19,  third; 
20,  fourth;  21,  origin  of  the  phi-enic  nerve,  22,  23,  fifth,  sixth,  seventh,  and  eighth  cervical  nerves, 
forming  with  the  first  dorsal  the  brachial  plexus;  24,  superior  cervical  ganglion  of  the  sympathetic; 
25,  middle  cervical  ganglion;  26,  inferior  cervical  ganglion  united  with  the  first  dorsal  ganglion;  27, 
28, 39, 30,  second,  third,  fourth,  and  fifth  dorsal  ganglia.  (From  Sappey  after  Hirschfeld  and  LeveiU6.) 


vagus  form  a  large  portion  of  the  supply  of  nerves  to  the  Heart  and  the 
great  Arteries  through  the  cardiac  nerves,  derived  from  both  the  trunk 
and  the  recurrent  nerve;  to  the  Lungs,  through  both  the  anterior  and 


148 


HAND-BOOK  OF  PHYSIOLOGY. 


the  posterior  pulmonary  plexuses;  and  to  the  Stomach,  by  its  terminal 
branches  passing  over  the  walls  of  that  organ;  while  branches  are  also 
distributed  to  the  Liver  and  to  the  Spleen. 

Communications. — Throughout  its  whole  course,  the  vagus  contains 
both  sensory  and  motor  fibres;  but  after  it  has  emerged  from  the  skull, 
and  in  some  instances  even  sooner,  it  enters  into  so  many  anastomoses 
that  it  is  hard  to  say  whether  the  filaments  it  contains  are,  from  their 
origin,  its  own,  or  whether  they  are  derived  from  other  nerves  combining 
with  it.  This  is  particularly  the  case  with  the  filaments  of  the  sympathetic 
nerve,  which  are  abundantly  added  to  nearly  all  its  branches.  The  likeness 
to  the  sympathetic  which  it  thus  acquires  is  further  increased  by  its  contain- 
ing many  filaments  derived,  not  from  the  brain,  but  from  its  own  petrosal 
ganglia,  in  which  filaments  originate,  in  the  same  manner  as  in  the  ganglia 
of  the  sympathetic,  so  abundantly  that  the  trunk  of  the  nerve  is  visibly 
larger  below  the  ganglia  than  above  them  (Bidder  and  Volkmann).  Next 
to  the  sympathetic  nerve,  that  which  most  communicates  with  the  vagus 
is  the  accessory  nerve,  whose  internal  branch  joins  its  trunk,  and  is  lost 
in  it. 

Functions. — The  most  probable  account  of  the  particular  functions 
which  the  branches  of  the  pneumogastric  nerve  discharge  in  the  several 
parts  to  which  they  are  distributed,  may  be  drawn  from  John  Eeid's  ex- 
periments on  dogs.  They  show  that, — 1.  The  pharyngeal  branch  is  the 
principal  motor  nerve  of  the  pharynx  and  soft  palate,  and  is  most  probably 
wholly  motor;  the  chief  part  of  its  motor  fibres  being  derived  from  the 
internal  branch  of  the  accessory  nerve.  2.  The  inferior  or  recurrent 
laryngeal  nerve  is  the  motor  nerve  of  the  larynx.  3.  The  superior  laryn- 
geal nerve  is  chiefly  sensory:  the  only  muscle  supplied  by  it  being  the 
crico-thyroid.  4.  The  motions  of  the  cesopliagus,  the  stomach  and  part 
of  the  small  intestines,  are  dependent  on  motor  fibres  of  the  vagus,  and  are 
probably  excited  by  impressions  made  upon  sensitive  fibres  of  the  same. 
5.  The  cardiac  branches  communicate,  from  the  centre  in  the  medullary 
channel,  impulses  (inhibitory)  regulating  the  action  of  the  heart.  0. 
The  pulmonary  branches  form  the  principal  channel  by  which  the  sensory 
impressions  on  the  mucous  surface  of  the  trachea,  bronchi  and  lungs  that 
influence  respiration  are  transmitted  to  the  medulla  oblongata;  and 
some  fibres  also  supply  motor  influence  to  the  muscular  portions  of  the 
fibres  of  the  trachea  and  bronchi.  7.  Branches  to  the  stomach  and  intes- 
tines not  only  convey  motor  but  also  vaso-motor  impulses  to  those  organs. 
8.  The  action  of  the  so-called  depressor  branch  (p.  154,  Vol.  I.)  in  inliih- 
iting  the  action  of  the  vaso-motor  centre  has  already  been  treated  of,  as 
has  also  the  influence  of  the  vagus  in  stimulating  the  secretion  of  the  sali- 
vary glands,  as  in  the  nausea  which  precedes  vomiting  (p.  232,  Vol.  I.). 
To  summarize,  tliercfore,  the  many  functions  of  this  nerve,  it  may  be  said 
that  it  supplies  motor  influence  to  the  })harynx  and  oesophagus,  to  stomach 


THE  NERVOUS  SYSTEM. 


149 


and  small  intestine,  and  to  the  larynx,  trachea,  bronchi  and  lung;  sensory 
and  in  part  vaso-motor  influence  to  the  same  regions;  inhibitory  influence 
to  the  heart;  inJiiiitory  afferent  impulses  to  the  vaso-motor  centre;  excito- 
secrefory  to  the  salivary  glands;  excito-motor  in  coughing,  vomiting,  etc. 

Effects  of  Section. — Division  of  both  vagi,  or  of  both  their  recur- 
rent branches,  is  often  very  quickly  fatal  in  young  animals;  but  in  old 
animals  the  division  of  the  recurrent  nerve  is  not  generally  fatal,  and 
that  of  both  the  vagi  is  not  always  fatal,  and,  when  it  is  so,  death  ensues 
slowly.  This  difference  is,  probably,  because  the  yielding  of  the  carti- 
lages of  the  larynx  in  young  animals  permits  the  glottis  to  be  closed  by  the 
atmospheric  pressure  in  inspiration,  and  they  are  thus  quickly  suffocated 
unless  tracheotomy  be  performed.  In  old  animals,  the  rigidity  and 
prominence  of  the  arytenoid  cartilages  prevent  the  glottis  from  being 
completely  closed  by  the  atmospheric  pressure;  even  when  all  the  muscles 
are  paralyzed,  a  portion  at  its  posterior  part  remains  open,  and  through 
this  the  animal  continues  to  breathe. 

In  the  case  of  slower  death,  after  division  of  both  the  vagi,  the  lungs 
are  commonly  found  gorged  with  blood,  cedemiatous,  or  nearly  solid,  with 
a  kind  of  low  pneumonia,  and  with  their  bronchial  tubes  full  of  frothy 
bloody  fluid  and  mucus,  changes  to  which,  in  general,  the  death  may  be 
proximately  ascribed.  These  changes  are  due,  perhaps  in  part,  to  the 
influence  which  the  nerves  exercise  on  the  movements  of  the  air-cells  and 
bronchi;  yet,  since  they  are  not  always  produced  in  one  lung  when  its 
nerve  is  divided,  they  cannot  be  ascribed  wholly  to  the  suspension  of 
organic  nervous  influence.  Eather,  they  may  be  ascribed  to  the  hindrance 
to  the  passage  of  blood  through  the  lungs,  in  consequence  of  the  dimin- 
ished supply  of  air  and  the  excess  of  carbonic  acid  in  the  air-cells  and  in 
the  pulmonary  capillaries;  in  part,  perhaps,  to  paralysis  of  the  blood- 
vessels, leading  to  congestion;  and  in  part,  also,  they  appear,  due  to  the 
passage  of  food  and  of  the  various  secretions  of  the  mouth  and  fauces 
through  the  glottis,  which,  being  deprived  of  its  sensibility,  is  no  longer 
stimulated  or  closed  in  consequence  of  their  contact. 

References  to  other  functions  of  Vagi. — Eegarding  the  influence  of  the 
vagus,  see  also  Heart  (p.  126,  Vol.  I.),  Arteries  (p.  154,  Vol.  I.),  Salivary 
Gland  (p.  232,  Vol.  I.),  Glottis  and  Larynx  (p.  202,  Vol.  I.),  Trachea  and 
Bronchi  (p.  183,  Vol.  I.),  Lungs  (p.  202,  Vol.  I.),  Pharynx  and  (Esophagus 
(p.  239,  Vol.  L),  Stomach  (p.  252,  Vol.  I.). 

Spin"al  Accessoey  Nekve. 

The  principal  branch  of  the  accessory  nerve,  its  external  branch,  sup- 
plies the  sterno-mastoid  and  trapezius  muscles;  and,  though  pain  is  produced 
by  irritating  it,  is  composed  almost  exclusively  of  motor  fibres.  It  is  very 
probable  that  the  accessory  nerve  gives  some  motor  filaments  to  the  vagus. 


150  HAND-BOOK  OF  PHYSIOLOGY, 

For,  among  the  experiments  made  on  this  point,  many  have  shown  that 
when  the  accessory  nerve  is  irritated  within  the  skull,  convulsive  move- 
ments ensue  in  some  of  the  muscles  of  the  larynx;  all  of  which,  as  already 
stated,  are  supplied,  apparently,  by  branches  of  the  vagus;  and  (which 
is  a  very  significant  fact)  Vrolik  states  that  in  the  chimpanzee  the  internal 
branch  of  the  accessory  does  not  join  the  vagus  at  all,  but  goes  direct  to 
the  larynx. 

Among  the  roots  of  the  accessory  nerve,  the  lower,  arising  from  the 
spinal  cord,  appear  to  be  composed  exclusively  of  motor  fibres,  and  to  be 
destined  entirely  to  the  trapezius  and  sterno-mastoid  muscles;  the  upper 
fibres,  arising  from  the  medulla  oblongata,  contain  many  sensory  as  well 
as  motor  fibres. 

Hypoglossal  Neeve. 

Distribution. — The  hypoglossal  or  ninth  nerve,  or  moto  Ungues, 
*  has  a  peculiar  relation  to  the  muscles  connected  with  the  hyoid  bone, 
including  those  of  the  tongue.  It  supplies  through  its  descending  branch 
{descende?is  7ioni),  the  sterno-hyoid,  sterno-thyroid,  and  omo -hyoid; 
through  a  special  branch  of  the  thyro-hyoid,  and  through  its  lingual 
branches  the  genio-hyoid,  stylo-glossus,  hyo-glossus,  and  genio-hyo-glossus, 
and  linguales.  It  contributes,  also,  to  the  supply  of  the  submaxillary 
gland. 

Functions. — The  function  of  the  hypoglossal  is  exclusively  motor, 
except  in  so  far  as  its  descending  branch  may  receive  a  few  sensory  fila- 
ments from  the  first  cervical  nerve.  As  a  motor  nerve,  its  influence  on 
all  the  muscles  enumerated  above  is  shown  by  their  convulsions  when  it 
is  irritated,  and  by  their  loss  of  power  when  it  is  paralyzed.  The  effects 
of  the  paralysis  of  one  hypoglossal  nerve  are,  however,  not  very  striking  in 
the  tongue.  Often,  in  cases  of  hemiplegia  involving  the  functions  of  the 
hypoglossal  nerve,  it  is  not  possible  to  observe  any  deviation  in  the  direc- 
tion of  the  protruded  tongue;  probably  because  the  tongue  is  so  compact 
and  firm  that  the  muscles  on  either  side,  their  insertion  being  nearly 
parallel  to  the  median  line,  can  push  it  straight  forward  or  turn  it  for 
some  distance  toward  either  side. 

Spinal  Nerves 

Functions. — Little  need  be  added  to  what  has  been  already  said  of 
these  nerves  (})p.  93  to  97,  Vol.  II.).  The  anterior  roots  of  the  spinal 
nerves  are  formed  cxc^lusively  of  motor  fibres;  the  posterior  roots  exclu- 
sively of  sensory  fibres.  Beyond  the  ganglia.,  all  tlie  spinal  nerves  are 
mixed  nerves,  jiiid  (lontain  as  well  sympathetic  filaments. 


THE  NEKVOUS  SYSTEM. 


151 


The  Sympathetic  Nerve. 

The  general  differences  between  the  fibres  of  the  cerebro-spinal  and 
sympathetic  nerves  have  been  already  stated  (pp.  71,  72,  Vol.  II.),  but 
the  different  modes  of  action  of  the  two  systems  cannot  be  referred  to  the 
different  structure  of  their  fibres.  It  is  probable,  however,  that  the  laws 
of  conduction  by  the  fibres  are  in  both  systems  the  same,  and  that  the 
differences  manifest  in  the  modes  of  action  of  the  systems  are  due  to  the 
multiplication  and  separation  of  the  nervous  centres  of  the  sympathetic: 
ganglia,  or  nerve-centres,  being  placed  in  connection  with  the  fibres  of 
the  sympathetic  in  nearly  all  parts  of  their  course. 

Distribution. — 1.  Fibres  are  distributed  to  all  plain  or  unstriped 
muscular  fibres,  as  those  of  the  blood-vessels  (vaso-motor  nerves),  of  the 
muscular  coats  of  the  intestines  and  other  hollow  viscera,  of  gland-ducts, 
of  the  iris  and  ciliary  muscle  in  the  eye,  and  elsewhere. 

The  vaso-motor  fibres  come  originally  from  the  vaso-motor  centre  in 
the  medulla  oblongata;  and,  issuing  from  the  spinal  cord,  communicate 
with  the  prse-vertebral  chain  of  ganglia,  and  are  thence,  as  branches 
from  these,  distributed  to  the  Blood-vessels.  2.  Fibres  (accelerating)  are 
distributed  to  the  Heart.  3.  Secretory  fibres  (in  addition  to  vaso-motor) 
are  distributed  to  the  salivary,  and  presumably  to  other  secreting  glands. 
4.  Intercentral  or  inter-ganglionic  fibres.  5.  Centripetal  fibres  proceed- 
ing to  the  vaso-motor  centre  in  the  medulla;  to  the  various  sympathetic 
ganglia;  and  probably  to  all  cerebro-spinal  nerve-centres.  The  periph- 
eral distribution  of  these  centripetal  fibres  is,  without  doubt,  chiefly  in 
the  parts  or  organs  to  which  the  centrifugal  fibres  of  the  same  sys- 
tem are  mainly  distributed.  But  they  are  also  present  in  all  those 
other  parts  of  the  body  which  belong  more  especially  to  the  Cerebro- 
spinal system. 

Structure. — The  sympathetic  ganglia  all  contain — (1),  nerve-fibres 
traversing  them;  (2),  nerve-fibres  originating  in  them;  (3),  nerve  or 
ganghon  corpuscles,  giving  origin  to  these  fibres;  and  (4),  other  corpuscles 
that  appear  free.  In  the  sympathetic  ganglia  of  the  frog,  ganglion-cells 
of  a  very  complicated  structure  have  been  described  by  Beale  and  sub- 
sequently by  Arnold.  The  cells  are  enclosed  each  in  a  nucleated  capsule: 
they  are  pyriform  in  shape,  and  from  the  pointed  end  two  fibres  are 
given  off,  which  gradually  acquire  the  characters  of  nerve-fibres:  one  of 
them  is  straight,  and  the  other  (which  sometimes  arises  from  the  cell  by 
two  roots)  is  spirally  coiled  around  it. 

In  the  trunk,  and  thence  proceeding  branches  of  the  sympathetic, 
there  appear  to  be  always— (1),  fibres  which  arise  in  its  own  ganglia;  (2), 
fibres  derived  from  the  ganglia  of  the  cerebral  and  spinal  nerves;  (3), 
fibres  derived  from  the  brain  and  spinal  cord  and  transmitted  through  the 


roots  of  their  nerves.  The 
spinal  cord,  indeed,  appears 
to  be  a  large  source  of  the 
fibres  of  the  sympathetic 
nerve. 

Through  the  commnni- 
cating  branches  between 
the  spinal  nerves  and  the 
prse-vertebral  sympathetic 
ganglia,  which  have  been 
generally  called  roots  or 
origins  of  the  sympathetic 
nerve,  an  interchange  is 
effected  between  all  the 
spinal  nerves  and  the  sym- 
pathetic trunks;  all  the  gan- 
glia, also,  which  are  seated 
on  the  cerebral  nerves, 
have  roots  (as  they  are 
called)  through  which  fila- 
ments of  the  cerebral  nerves 
are  added  to  their  own.  So 
that,  probably,  all  sympa- 
thetic nerves  contain  some 
intermingled  cerebral  or 
spinal  nerve-fibres;  and  all 
cerebral  and  spinal  nerves, 
some  filaments  derived 
from  the  sympathetic  sys- 
tem or  from  ganglia.  But 
the  proportions  in  whicli 
these  filaments  are  mingled  . 
are  not  uniform.  The 
nerves  which  arise  from  the 
brain  and  spinal  cord  retain 
throughout  their  course 
and  distribution  a  prepon- 
derance of  cerchro- spinal 
fibres,  Avhile  the  nerves  iui- 
mcdiately  arising  from  the 
so-called  sympathetic  gan- 
glia probably  contain  a  ma- 
jority of  sympalltcfic  fibres. 
J^ut  inasnnicli  ns  is 


THE  NERVOUS  SYSTEM. 


153 


no  certainty  that  in  structure  the  branches  of  cerebral  or  spinal  nerves 
differ  always  from  those  of  the  sympathetic  system,  it  is  impossible  in 
the  present  state  of  our  knowledge  to  be  sure  of  the  source  of  fibres 
which  from  their  structure  might  lead  the  observer  to  believe  that  they 
arose  from  the  brain  or  spinal  cord  on  the  one  hand,  or  from  the  sym- 
pathetic ganglia  on  the  other.  In  other  words,  although  the  large  white 
medullated  fibres  are  especially  characteristic  of  cerebro-spinal  nerves,  and 
the  pale  or  non-medullated  fibres  of  a  sympathetic  nerve,  in  which  they 
largely  preponderate,  there  is  no  certainty  to  be  obtained  in  a  doubtful 
€ase,  of  whether  the  nerve-fibre  is  derived  from  one  or  the  other,  from 
mere  examination  of  its  structure.    It  may  be  derived  from  either  source. 

Functions. — It  may  be  stated  generally  that  the  sympathetic  nerve- 
fibres  are  simple  conductors  of  impressions,  as  are  those  of  the  Cerebro- 
spinal system;  and  that  the  ganglionic  centres  have  (each  in  its  appropri- 
ate sphere)  the  like  powers  both  of  conducting,  transferring,  reflecting, 
and  possibly  of  augmenting  or  of  inhihiting  impressions  made  on  them. 

The  power  possessed  by  the  sympathetic  ganglia  of  conducting  impres- 
sions is  sufficiently  proved  in  disease,  as  when  any  of  the  viscera,  usually 
xmfelt,  give  rise  to  sensations  of  pain,  or  when  a  part  not  commonly  sub- 
ject to  mental  influence  is  excited  or  retarded  in  its  actions  by  the  vari- 
ous conditions  of  the  mind;  for  in  all  these  cases  impressions  must  be 
conducted  to  and  fro  through  the  whole  distance  between  the  part  and 
the  spinal  cord  and  brain.     So,  also,  in  experiments,  now  more  than 


Fig.  348.— Diagrammatic  view  of  the  Sympathetic  cord  of  the  right  side,  showing  its  connections 
"With  the  principal  cerebro-spinal  nerves  and  the  main  praeaortic  plexuses.  1-4.  (From  Quain's 
Anatomy.) 

Cerebrospinal  nerves. — VI,  a  portion  of  the  sixth  cranial  as  it  passes  through  the  cavernous 
sinus,  receiving  two  twigs  from  the  carotid  plexus  of  the  sympathetic  nerve;  O,  ophthalmic  ganglion 
■connected  by  a  twig  with  the  carotid  plexus;  M,  connection  of  the  spheno-palatine  ganglion  by  the 
Vidian  nerve  with  the  carotid  plexus;  C,  cervical  plexus;  Br,  brachial  plexus;  D  6,  sixth  intei'costal 
nerve;  D  12,  twelfth;  L  3,  third  lumbar  nerve;  S  1,  first  sacral  nerve;  S  3,  third;  S  5,  fifth;  Cr,  an- 
terior crural  nerve;  Cr',  great  sciatic;  pn,  pneumogastric  nerve  in  the  lower  part  of  the  neck;  ?%  re- 
current nerve  winding  round  the  subclavian  artery. 

Sympathetic  Cord.—c,  superior  cervical  ganglion;  c',  second  or  middle;  c",  inferior:  from  each  of 
these  ganglia  cardiac  nerves  (all  deep  on  this  side)  are  seen  descending  to  the  cardiac  plexus;  d  1, 
placed  immediately  below  the  first  dorsal  sympathetic  gangUon;  d  6,  is  opposite  the  sixth;  1 1,  first 
lumbar  gangUon;  c  g,  the  terminal  or  coccygeal  ganglion. 

Praeaortic  and  Visceral  Plexuses.— p  p^  pharyngeal,  and,  lower  down,  laryngeal  plexus ;  pi,  pos- 
terior pulmonary  plexus  spreading  from  the  vagus  on  the  back  of  the  right  bronchus;  c  a,  on  the 
aorta,  the  cardiac  plexus,  toward  which,  in  addition  to  the  cardiac  nerves  from  the  three  cervical 
sympathetic  ganglia,  other  branches  are  seen  descending  from  the  vagus  and  recurrent  nerves;  co, 
right  or  posterior,  and  co',  left  or  anterior  coronary  plexus;  o,  oesophageal  plexus  in  long  meshes  on 
the  gullet;  sp,  great  splanchnic  nerve  formed  by  branches  from  the  fifth,  sixth,  seventh,  eighth,  and 
ninth  dorsal  ganglia;  + ,  small  splanchnic  from  the  ninth  and  tenth;  +  + ,  smallest  or  third  splanch- 
nic from  the  eleventh:  the  first  and  second  of  these  are  shown  joining  the  solar  plexus,  s  o;  the  third 
descending  to  the  renal  plexus,  r  e;  connecting  branches  between  the  solar  plexus  and  the  vagi  are 
also  represented;  pn',  above  the  place  where  the  right  vagus  passes  to  the  lower  or  posterior  surf  ace 
of  the  stomach;  pw",  the  left  distributed  on  the  anterior  or  upper  surface  of  the  cardiac  portion  of 
the  organ:  from  the  solar  plexus  large  branches  are  seen  surrounding  the  arteries  of  the  coeliac  axis, 
and  descending  to  m  s,  the  superior  mesenteric  plexus;  opposite  to  this  is  an  indication  of  the  supra- 
renal plexus;  below  r  e  (the  renal  plexus),  the  spermatic  plexus  is  also  indicated;  a  o,  on  the 
front  of  the  aorta,  marks  the  aortic  plexus,  formed  by  nerves  descending  from  the  solar  and  supe- 
rior mesenteric  plexuses  and  from  the  lumbar  ganglia;  mi,  the  inferior  mesenteric  plexus  sur- 
rounding the  corresponding  artery ;  hy,  hypogastric  plexus  placed  between  the  common  iliac  vessels, 
connected  above  with  the  aortic  plexus,  receiving  nerves  from  the  lower  lumbar  ganglia,  and  dividing 
below  into  the  right  and  left  pelvic  or  inferior  hypogastric  plexuses;  pi,  the  right  pelvic  plexus; 
irom  this  the  nerves  descending  are  joined  by  those  from  the  plexus  on  the  superior  hemorrhoidal 
vessels,  mi' ,  by  sympathetic  nerves  from  the  sacral  ganglia,  and  by  numerous  visceral  nerves  from 
the  third  and  fourth  sacral  spinal  nerves,  and  there  are  thus  formed  the  rectal,  vesical,  and  other 
plexuses,  which  ramify  upon  the  viscera  from  behind  forward  and  from  below  upward,  as  toward 
ir,  and  v,  the  rectum  and  bladder. 


154 


HAND-BOOK  OF  PHYSIOLOGY. 


sufficiently  numerous^  irritations  of  the  semilunar  ganglia,  the  splanchnic 
nerves,  the  thoracic,  hepatic,  and  other  ganglia  and  nerves,  have  elicited 
expressions  of  pain,  and  have  excited  movements  in  the  muscular  organs 
supplied  from  the  irritated  part. 

In  the  case  of  pain,  or  of  movements  affected  by  mental  conditions,  it 
may  be  supposed  that  the  conduction  of  impressions  is  effected  through 
the  cerebro-spinal  fibres  which  are  mingled  in  all,  or  nearly  all,  parts  of 
the  sympathetic  nerves.  There  are  no  means  of  deciding  this;  but  if  it 
be  admitted  that  the  conduction  is  effected  through  the  cerebro-spinal 
nerve-fibres,  then,  whether  or  not  they  pass  uninterruptedly  between  the 
brain  or  spinal  cord  and  the  part  affected,  it  must  be  assumed  that  their 
mode  of  conduction  is  modified  by  the  ganglia.  For,  if  such  cerebro- 
spinal fibres  are  conducted  in  the  ordinary  manner,  the  parts  should  be 
always  sensible  and  liable  to  the  influence  of  the  will,  and  impressions 
should  be  conveyed  to  and  fro  instantaneously.  But  this  is  not  the  case; 
on  the  contrary,  through  the  branches  of  the  sympathetic  nerve  and  its 
ganglia,  none  but  intense  impressions,  or  impressions  exaggerated  by  the 
morbid  excitability  of  the  nerves  or  ganglia,  can  be  conveyed. 

Respecting  the  general  action  of  the  ganglia  of  the  sympathetic  nerve, 
in  reflex  or  other  actions,  little  need  be  said  here,  since  they  may  be  taken 
as  examples  by  which  to  illustrate  the  common  modes  of  action  of  all 
nerve-centres  (see  p.  83,  Vol.  II.).  Indeed,  complex  as  the  sympathetic 
system,  taken  as  a  whole,  is,  it  presents  in  each  of  its  parts  a  simplicity 
not  to  be  found  in  the  cerebro-spinal  system:  for  each  ganglion  with 
afferent  and  efferent  nerves  forms  a  simple  nervous  system,  and  might 
serve  for  the  illustration  of  all  the  nervous  actions  with  which  the  mind 
is  unconnected. 

The  parts  principally  supplied  with  sympathetic  nerves  are  usually 
capable  of  none  but  involuntary  movements,  and  when  the  mind  acts  on 
them  at  all,  it  is  only  through  the  strong  excitement  or  depressing  influ- 
ence of  some  passion,  or  through  some  voluntary  movement  with  which 
the  actions  of  the  involuntary  part  are  commonly  associated.  The  heart, 
stomach,  and  intestines  are  examples  of  these  statements;  for  the  heart 
and  stomach,  though  supplied  in  large  measure  from  the  pneumogastric 
nerves,  yet  probably  derive  through  them  few  filaments  except  such  as 
have  arisen  from  their  ganglia,  and  are  therefore  of  the  nature  of  sym- 
pathetic fibres. 

The  parts  which  are  supplied  with  motor  power  by  the  sympathetic  nerve 
continue  to  move,  though  more  feebly  than  before,  when  they  are  sepa- 
rated from  their  natural  connections  with  the  rest  of  the  sympathetic  sys- 
tem, and  wholly  removed  from  the  body.  Thus,  the  heart,  after  it  is  taken 
from  the  body,  continues  to  beat  in  Mammalia  for  one  or  two  minutes, 
in  reptiles  and  Amphibia  for  hours;  and  the  peristaltic  motions  of  the 
intestine  continue  under  the  same  circumstances.    IToncc  the  motions  of 


THE  JSTERVOUS  SYSTEM. 


155 


the  parts  supplied  with  nerves  from  the  sympathetic  are  shown  to  be,  in 
a  measure,  independent  of  the  brain  and  spinal  cord;  this  independent 
maintenance  of  their  action  being,  without  doubt,  due  to  the  fact  that 
they  contain,  in  their  own  substance,  the  apparatus  of  ganglia  and  nerve- 
fibres  by  which  their  motions  are  immediately  governed. 

It  seems  to  be  a  general  rule,  at  least  in  animals  that  have  both  cere- 
bro-spinal  and  sympathetic  nerves  much  developed,  that  the  involuntary 
movements  excited  by  stimuli  conveyed  through  ganglia  are  orderly  and 
like  natural  movements,  while  those  excited  through  nerves  without 
ganglia  are  convulsive  and  disorderly;  and  the  probability  is  that,  in  the 
natural  state,  it  is  through  the  same  ganglia  that  natural  stimuli,  impress- 
ing centripetal  nerves,  are  reflected  through  centrifugal  nerves  to  the 
involuntary  muscles.  As  the  muscles  of  respiration  are  maintained  in 
uniform  rhythmic  action  chiefly  by  the  reflecting  and  combining  power 
of  the  medulla  oblongata,  so  are  those  of  the  heart,  stomach,  and  intes- 
tines, by  their  several  ganglia.  And  as  with  the  ganglia  of  the  sympa- 
thetic and  their  nerves,  so  with  the  medulla  oblongata  and  its  nerves  dis- 
tributed to  the  respiratory  muscles, — if  these  nerves  of  the  medulla 
oblongata  itself  be  directly  stimulated,  the  movements  that  follow  are  con- 
vulsive and  disorderly;  but  if  the  medulla  be  stimulated  through  a  cen- 
tripetal nerve,  as  when  cold  is  applied  to  the  skin,  then  the  impressions 
are  reflected  so  as  to  j)roduce  movements  which,  though  they  may  be  very 
quick  and  almost  convulsive,  are  yet  combined  in  the  plan  of  the  proper 
respiratory  acts. 

Among  the  ganglia  of  the  sympathetic  nerves  to  which  this  co-ordina- 
tion of  movements  is  to  be  ascribed,  must  be  reckoned,  not  those  alone 
which  are  on  the  principal  trunks  and  branches  of  the  sympathetic  ex- 
ternal to  any  organ,  but  those  also  which  lie  in  the  very  substance  of  the 
organs;  such  as  those  of  the  heart  (p.  125,  Vol.  I.).  Those  also  may  be 
included  which  have  been  found  in  the  mesentery  close  by  the  intestines, 
as  well  as  in  the  muscular  and  sub-mucous  tissue  of  the  stomach  and  in- 
testinal canal  (pp.  244,  255,  Vol.  I.),  and  in  other  parts.  The  extension 
of  discoveries  of  such  ganglia  will  probably  diminish  yet  further  the  num- 
ber of  instances  in  which  the  involuntary  movements  appear  to  be  effected 
independently  of  nervous  influence. 

Eespecting  the  influence  of  the  sympathetic  system  on  various  physi- 
ological processes,  see  Heart  (p.  127,  Vol.  I.),  Arteries  (p.  152,  Vol.  I.), 
Animal  Heat  (p.  316,  Vol.  I.),  Salivary  Glands  (p.  233,  Vol.  L),  Stomach, 
(p.  252,  Vol.  I.),  Intestines  (p.  255,  Vol.  I.).  These  are  parts  which  have 
been  specially  investigated.  But  they  are  not  in  any  way  exceptional. 
All  physiological  processes  must,  of  necessity,  either  directly  or  through 
vaso-motor  fibres,  be  under  the  influence  of  the  Sympathetic  system. 

Influence  of  the  Nervous  System  on  Nutrition. — It  has  been 
held  that  the  nervous  system  cannot  be  essential  to  a  healthy  course  of 


156 


HAND-BOOK   OF  PHYSIOLOGY. 


nutrition^  because  in  plants  and  tlie  early  embryo^  and  in  the  lowest 
animals^  in  wliicli  no  nervous  system  is  developed,  nutrition  goes  on  with- 
out it.  But  this  is  no  proof  that  in  animals  which  have  a  nervous  system, 
nutrition  may  be  independent  of  it;  rather,  it  may  be  assumed,  that  in 
ascending-  development,  as  one  system  after  another  is  added  or  in- 
creased, so  the  highest  (and,  highest  of  all,  the  nervous  system)  will 
always  be  inserted  and  blended  in  a  more  and  more  intimate  relation  with 
all  the  rest;  according  to  the  general  law,  that  the  interdependence  of 
parts  augments  with  their  development. 

The  reasonableness  of  this  assumption  is  proved  by  many  facts  show- 
ing the  influence  of  the  nervous  system  on  nutrition,  and  by  the  most 
striking  of  these  facts  being  observed  in  the  higher  animals,  and  especially 
in  man.  The  influence  of  the  mind  in  the  production,  aggravation,  and 
cure  of  organic  diseases  is  matter  of  daily  observation,  and  a  sufficient 
proof  of  influence  exercised  on  nutrition  through  the  nervous  system. 

Independently  of  mental  influence,  injuries  either  to  portions  of  the 
nervous  centres,  or  to  individual  nerves,  are  frequently  followed  by  de- 
fective nutrition  of  the  -parts  supplied  by  the  injured  nerves,  or  deriving 
their  nervous  influence  from  the  damaged  portions  of  the  nervous  centres. 
Thus,  lesions  of  the  spinal  cord  are  sometimes  followed  by  mortification 
of  portions  of  the  paralyzed  parts;  and  this  may  take  place  very  quickly, 
as  in  a  case  in  wdiich  the  ankle  sloughed  within  twenty-four  hours  after 
an  injury  of  the  spine.  After  such  lesions  also,  the  repair  of  injuries  in 
the  paralyzed  parts  may  take  place  less  completely  than  in  others;  so,  in 
a  case  in  which  paraplegia  was  produced  by  fracture  of  the  lumbar  verte- 
brse,  and,  in  the  same  accident,  the  humerus  and  tibia  were  fractured. 
The  former  in  due' time  united:  the  latter  did  not.  The  same  fact  was 
illustrated  by  some  experiments,  in  which  having,  in  salamanders,  cut  off 
the  end  of  the  tail,  and  then  thrust  a  thin  wire  some  distance  up  the 
spinal  canal,  so  as  to  destroy  the  cord,  it  was  found  that  the  end  of  the 
tail  was  reproduced  more  slowly  than  in  other  salamanders  in  whom  the 
spinal  cord  w^as  left  uninjured  above  the  point  at  wdiich  the  tail  was  ampu- 
tated. Illustrations  of  the  same  kind  are  furnished  by  the  several  cases 
in  which  division  or  destruction  of  the  trunk  of  the  trigeminal  nerve  has 
been  followed  by  incomplete  and  morbid  nutrition  of  the  corresponding 
side  of  the  face;  ulceration  of  the  cornea  being  often  directly  or  indirectly 
one  of  the  consequences  of  such  imperfect  nutrition.  Part  of  the  wasting 
<ind  slow  degeneration  of  tissue  in  paralyzed  limbs  is  probably  referable 
also  to  the  withdrawal  of  nervous  influence  from  them;  though,  perhaps, 
more  is  due  to  the  want  of  use  of  the  tissues. 

Undue  irritation  of  the  trunks  of  nerves,  as  well  as  their  division  or 
destruction,  is  sometimes  followed  by  defective  or  morbid  nutrition.  To 
this  may  be  referred  the  cases  in  Avhich  ulceration  of  tlie  parts  supplied 
by  the  irritated  nerves  occni-s  iVoqnently,  and  continues  so  long  as  the 


THE  NERVOUS  SYSTEM. 


157 


irritation  lasts.  Further  evidence  of  the  influence  of  the  nervous  system 
upon  nutrition  is  furnished  by  those  cases  ir  which,  from  mental  anguish, 
or  in  severe  neuralgic  headaches,  the  hair  becomes'  grey  very  quickly,  or 
even  in  a  few  hours. 

So  many  and  varied  facts  leave  little  doubt  that  the  nervous  system 
exercises  an  influence  over  nutrition  as  over  other  organic  processes;  and 
they  cannot  be  easily  explained  by  supposing  that  the  changes  in  the 
nutritive  processes  are  only  due  to  the  variations  in  the  size  of  the  blood- 
vessels supplying  the  affected  parts,  although  this  is,  doubtless,  one  im- 
portant element  in  producing  the  result. 

The  question  remains,  through  what  class  of  nerves  is  the  influence 
exerted?  When  defective  nutrition  occurs  in  parts  rendered  inactive  by 
injury  of  the  motor  nerve  alone,  as  in  the  muscles  and  other  tissues  of  a 
paralyzed  face  or  limb,  it  may  appear  as  if  the  atrophy  were  the  direct 
consequence  of  the  loss  of  power  in  the  motor  nerves;  but  it  is  more  prob- 
able that  the  atrophy  is  the  consequence  of  the  want  of  exercise  of  the 
parts;  for  if  the  muscles  be  exercised  by  artificial  irritation  of  their  nerves 
their  nutrition  will  be  less  defective.  The  defect  of  the  nutritive  process 
which  ensues  in  the  face  and  other  parts,  however,  in  consequence  of 
destruction  of  the  trigeminal  nerve,  cannot  be  referred  to  loss  of  influence 
of  any  motor  nerves;  for  the  motor-nerves  of  the  face  and  eye,  as  well  as 
the  olfactory  and  optic,  have  no  share  in  the  defective  nutrition  which 
follows  injury  of  the  trigeminal  nerve;  and  one  or  all  of  them  may  be 
destroyed  without  any  direct  disturbance  of  the  nutrition  of  the  parts 
they  severally  supply. 

It  must  be  concluded,  therefore,  that  the  influence  which  is  exercised 
by  nerves  over  the  nutrition  of  parts  to  which  they  are  distributed  is  to 
be  referred,  in  part  or  altogether,  either  to  the  nerves  of  common  sensa- 
tion, or  to  the  vaso-motor  nerves,  or,  as  it  is  by  some  supposed,  to  nerve 
fibres  {trophic  nerves),  which  preside  specially  over  the  nutrition  of  the 
tissues  and  organs  to  which  they  are  supplied. 

It  is  not  at  present  possible  to  say  whether  the  influence  on  nutrition 
is  exercised  through  the  cerebro-spinal  or  through  the  sympathetic  nerves, 
which,  in  the  parts  on  which  the  observation  has  been  made,  are  generally 
combined  in  the  same  sheath.  The  truth  perhaps  is,  that  it  may  be  ex- 
erted through  either  or  both  of  these  nerves.  The  defect  of  nutrition 
which  ensues  after  lesion  of  the  spinal  cord  alone,  the  sympathetic  nerves 
being  uninjured,  and  the  general  atrophy  which  sometimes  occurs  in  con- 
sequence of  diseases  of  the  brain,  seem  to  prove  the  influence  of  the 
cerebro-spinal  system:  while  the  observation  that  inflammation  of  the  eye 
is  a  constant  result  of  ligature  of  the  sympathetic  nerve  in  the  neck,  and 
many  other  observations  of  a  similar  kind,  exhibit  very  well  the  influence 
of  the  latter  nerve  in  nutrition. 


CHAPTEE  XIX. 


THE  SENSES. 

Through  the  medium  of  the  Nervous  system  the  mind  obtains  a 
knowledge  of  the  existence  both  of  the  various  parts  of  the  body,  and  of 
the  external  world.  This  knowledge  is  based  upon  sensations  resulting 
from  the  stimulation  of  certain  centres  in  the  brain,  by  irritations  con- 
veyed to  them  by  afferent  (sensory)  nerves.  Under  normal  circumstances, 
the  following  structures  are  necessary  for  sensation:  {a)  A  peripheral 
organ  for  the  reception  of  the  impression;  (J)  a  nerve  for  conducting  it; 
(c)  a  nerve-centre  for  feeling  or  perceiving  it. 

Classification  of  Sensations. — Sensations  may  be  conveniently 
classed  as  (1)  common,  and  (2)  special. 

(1.)  Common  Sensations. — Under  this  head  fall  all  those  general  sen- 
sations which  cannot  be  distinctly  localized  in  any  particular  part  of  the 
body,  such  as  Fatigue,  Discomfort,  Faintness,  Satiety,  together  with 
Hunger  and  Thirst,  in  which,  in  addition  to  a  general  discomfort,  there 
is  in  many  persons  a  distinct  sensation  referred  to  the  stomach  or  fauces. 
In  this  class  must  also  be  placed  the  various  irritations  of  the  mucous  mem- 
brane of  the  bronchi,  which  give  rise  to  coughing,  and  also  the  sensations 
derived  from  various  viscera  indicating  the  necessity  of  expelling  their 
contents;  e.g.,  the  desire  to  defaecate,  to  urinate,  and,  in  the  female,  the 
sensations  which  precede  the  expulsion  of  the  foetus.  We  must  also  include 
such  sensations  as  itching,  creeping,  tickling,  tingling,  burning,  aching, 
etc.,  some  of  which  come  under  the  head  of  pain:  they  will  be  again  referred 
to  in  describing  the  sense  of  Touch.  It  is  impossible  to  draw  a  very  clear 
line  of  demarcation  between  many  of  the  common  sensations  above  men- 
tioned, and  the  sense  of  Touch,  which  forms  the  connecting  link  between 
the  general  and  special  sensations.  Touch  is,  indeed,  usually  classed  with 
the  special  senses,  and  will  be  considered  in  the  same  group  with  them; 
yet  it  differs  from  them  in  being  common  to  many  nerves,  e.g.,  all  the 
sensory  spinal  nerves,  the  vagus,  glosso-pharyngeal,  and  fifth  cerebral 
nerves,  and  in  its  impressions  being  communicable  through  many  organs. 
Among  common  sensations  must  also  be  ranked  the  muscular  sense, 
which  has  been  already  alliulcd  to.  It  is  by  mean's  of  this  sense  that  we 
become  aware  of  the  condition  of  contraction  or  relaxation  of  the  various 
muscles  and  groups  of  muscles,  and  tlius  obtain  the  information  necessary 


THE  SENSES. 


159 


for  their  adjustment  to  various  purposes — standing,  walking,  grasping, 
etc.  This  muscular  sensibility  is  shown  in  our  power  to  estimate  the  dif- 
ferences between  weights  by  the  different  muscular  efforts  necessary  to 
raise  them.  Considerable  delicacy  may  be  attained  by  practice,  and  the 
difference  between  19^  oz.  in  one  hand  and  20  oz.  in  the  other  is  readily 
appreciated  (Weber). 

This  sensibility  with  whicn  the  muscles  are  endowed  must  be  carefully 
distinguished  from  the  sense  of  contact  and  of  pressure,  of  which  the 
skin  is  the  organ.  When  standing  erect,  we  can  feel  the  ground  (con- 
tact), and  further  there  is  a  sense  of  pressure,  due  to  our  feet  being 
pressed  against  the  ground  by  the  weight  of  the  body.  Both  these  are 
derived  from  the  skin  of  the  sole  of  the  foot.  If  now  we  raise  the  body 
on  the  toes,  we  are  conscious  (muscular  sense)  of  a  muscular  effort  made 
by  the  muscles  of  the  calf,  which  overcomes  a  certain  resistance. 

(2.)  Si^ecial  Sensations. — Including  the  sense  of  touch,  the  special 
senses  are  five  in  number — Touch,  Taste,  Smell,  Hearing,  Sight. 

Difference  between  Common  and  Special  Sensations.— The 
most  important  distinction  between  common  and  special  sensations  is  that 
by  the  former  we  are  made  aware  of  certain  conditions  of  various  parts  of 
•our  bodies,  while  from  the  latter  we  gain  our  knowledge  of  the  external 
world  also.  This  difference  will  be  clear  if  we  compare  the  sensations  of 
pain  and  touch,  the  former  of  which  is  a  common,  the  latter  a  special 
sensation.  ''If  we  place  the  edge  of  a  sharp  knife  on  the  skin,  we  feel 
the  edge  by  means  of  our  sense  of  touch;  we  perceive  a  sensation,  and  refer 
it  to  the  object  which  has  caused  it.  But  as  soon  as  we  cut  the  skin  with 
the  knife,  we  feel  pain,  a  feeling  which  we  no  longer  refer  to  the  cutting 
knife,  but  which  we  feel  within  ourselves,  and  which  communicates  to 
us  the  fact  of  a  change  of  condition  in  our  own  body.  By  the  sensation 
of  pain  we  are  neither  able  to  recognize  the  object  which  caused  it,  nor 
its  nature'^  (Weber). 

General  Characteristics:  Seat. — In  studying  the  phenomena  of 
sensation,  it  is  important  clearly  to  understand  that  the  Sensorium,  or 
seat  of  sensation,  is  in  the  Brain,  and  not  in  the  particular  organ  (eye, 
ear,  etc.)  through  which  the  sensory  impression  is  received.  In  com- 
mon parlance  we  are  said  to  see  with  the  eye,  hear  with  the  ear,  etc.,  but 
in  reality  these  organs  are  only  adapted  to  receive  impressions  which  are 
conducted  to  the  sensorium,  through  the  optic  and  auditory  nerves  re- 
spectively, and  there  give  rise  to  sensation. 

Hence,  if  the  optic  nerve  is  severed  (although  the  eye  itself  is  per- 
fectly uninjured),  vision  is  no  longer  possible;  since,  although  the  image 
falls  on  the  retina  as  before,  the  sensory  impression  can  no  longer  be  con- 
veyed to  the  sensorium.  When  any  given  sensation  is  felt,  all  that  we  can 
with  certainty  affirm  is  that  the  sensorium  in  the  brain  is  excited.  The 
exciting  cause  may  be  (in  the  vast  majority  of  cases  is),  some  object  of 


160 


HAND-BOOK  OF  PHYSIOLOGY. 


the  external  world  {objective  sensation);  or  the  condition  of  the  sensorium 
may  be  due  to  some  excitement  within  the  brain,  in  which  case  the  sen- 
sation is  termed  subjective.  The  mind  habitually  refers  sensations  to 
external  causes;  and  hence,  whenever  they  are  subjective  (due  to  causes, 
within  the  brain),  we  can  hardly  divest  ourselves  of  the  idea  of  an  ex- 
ternal cause,  and  an  illusion  is  the  result. 

Illusions. — Numberless  examples  of  such  illusions  might  be  quoted. 
As  familiar  cases  may  be  mentioned,  humming  and  buzzing  in  the  ears 
caused  by  some  irritation  of  the  auditory  nerve  or  centre,  and  even  musi- 
cal sounds  and  voices  (sometimes  termed  auditory  spectra);  also  so-called 
optical  illusions:  persons  and  other  objects  are  described  as  being  seen, 
although  not  present.  Such  illusions  are  most  strikingly  exemplified  in 
cases  of  delirium  tremens  or  other  forms  of  delirium,  in  which  cats,  rats, 
creeping  loathsome  forms,  etc.,  are  described  by  the  patient  as  seen  with 
great  vividness. 

Causes  of  Illusions. — One  uniform  internal  cause,  which  may  act 
on  all  the  nerves  of  the  senses  in  the  same  manner,  is  the  accumulation 
of  blood  in  their  capillary  vessels,  as  in  congestion  and  inflammation. 
This  one  cause  excites  in  the  retina,  while  the  eyes  are  closed,  the  sensa- 
tions  of  light  and  luminous  flashes;  in  the  auditory  nerve,  the  sensation 
of  humming  and  ringing  sounds;  in  the  olfactory  nerve,  the  sense  of 
odors;  and  in  the  nerves  of  feeling,  the  sensation  of  pain.  In  the  same 
way,  also,  a  narcotic  substance,  introduced  into  the  blood,  excites  in  the 
nerves  of  each  sense  peculiar  symptoms:  m  the  optic  nerves,  the  appear- 
ance of  luminous  sparks  before  the  eyes;  in  the  auditory  nerves,  '^tinnitus 
aurium";  and  in  the  common  sensory  nerves,  the  sensation  of  creeping  over 
the  surface.  So,  also,  among  external  causes,  the  stimulus  of  electricity, 
or  the  mechanical  influence  of  a  blow,  concussion,  or  pressure,  excites  in 
the  eye  the  sensation  of  light  and  colors;  in  the  ear,  a  sense  of  a  loud 
sound  or  of  ringing;  in  the  tongue,  a  saline  or  acid  taste;  and  in  the 
other  parts  of  the  body,  a  perception  of  peculiar  jarring  or  of  the  mechan- 
ical impression,  or  a  shock  like  it. 

Sensations  and  Perceptions. — The  habit  of  constantly  referring 
our  sensations  to  external  causes,  leads  us  to  interpret  the  various  modifi- 
cations which  external  objects  produce  in"  our  sensations,  as  properties 
of  the  external  bodies  themselves.  Thus  we  speak  of  certain  substances 
as  possessing  a  disagreeable  taste  and  smell;  whereas,  the  fact  is,  their 
taste  and  smell  are  only  disagreeable  to  us.  It  is  evident,  however,  tliat  on 
this  habit  of  referring  our  sensations  to  causes  outside  ourselves  (percep- 
tion), depends  the  reality  of  the  external  Avorld  to  us;  and  more  especially  is 
this  the  case  with  the  senses  of  touch  and  sight.  By  the  co-operation  of 
these  two  senses  aided  by  the  others,  we  arc  enabled  gradually  to  attain 
a  knowledge  of  external  objects  which  daily  experience  confirms,  until  we 


THE  SENSES. 


161 


come  to  place  unbounded  confidence  in  hat  is  termed  the  * 'evidence  of 
the  senses/' 

Judgments. — We  must  draw  a  distinction  between  mere  sensations, 
and  the  judgments  based,  often  unconsciously,  upon  them.  Thus,  in 
looking  at  a  near  object,  we  unconsciously  estimate  its  distance,  and  say 
it  seems  to  be  ten  or  twelve  feet  off:  but  the  estimate  of  its  distance  is  in 
reality  a  judgment  based  on  many  things  besides  the  appearance  of  the 
object  itself;  among  which  may  be  mentioned  the  number  of  intervening 
objects,  the  number  of  steps  which  from  past  experience  we  know  we 
must  take  before  we  could  touch  it,  and  many  others. 

Symptoms  of  Irritation  of  Nerves  of  Special  Sense. — Irritation 
of  the  optic  nerve,  as  by  cutting  it,  invariably  produces  a  sensation  of 
light,  of  the  auditory  nerve  a  sensation  of  some  modification  of  sound. 
Doubtless  these  distinct  sensations  depend  not  on  any  specialty  in  the 
structure  of  the  nerves  of  special  sense,  but  on  the  nature  of  their  con- 
nections in  the  sensorium. 

Experiments  seem  to  have  proved  that  none  of  these  nerves  possess  the 
faculty  of  common  sensibility.  Thus,  Magendie  observed  that  when  the 
olfactory  nerves,  laid  bare  in  a  dog,  were  pricked,  no  signs  of  pain  were 
manifested;  and  other  experiments  of  his  seem  to  show  that  both  the 
retina  and  optic  nerve  are  insusceptible  of  pain.  Further,  the  optic 
nerve  is  insusceptible  to  the  stimulus  of  light  when  severed  from  its  con- 
nection with  the  retina,  which  alone  is  adapted  to  receive  luminous  im- 
pressions. 

Sensation  of  Motion  is,  like  motion  itself,  of  two  kinds, — progres- 
sive and  vibratory.  The  faculty  of  the  perception  of  progressive  motion 
is  possessed  chiefly  by  the  senses  of  vision,  touch,  and  taste.  Thus  an 
impression  is  perceived  traveling  from  one  part  of  the  retina  to  another, 
and  the  movement  of  the  image  is  interpreted  by  the  mind  as  the  motion 
of  the  object.  The  same  is  the  case  in  the  sense  of  touch;  so  also  the 
movement  of  a  sensation  of  taste  over  the  surface  of  the  organ  of  taste, 
can  be  recognized.  The  motion  of  tremors,  or  vibrations,  is  perceived  by 
several  senses,  but  especially  by  those  of  hearing  and  touch. 

Sensations  of  Chemical  Actions. — We  are  made  acquainted  with 
chemical  actions  principally  by  taste,  smell,  and  touch,  and  by  each  of 
these  senses  in  the  mode  proper  to  it.    Volatile  bodies,  disturbing  the 

I     conditions  of  the  nerves  by  a  chemical  action,  exert  the  greatest  influ- 
ence  upon  the  organ  of  smell;  and  many  matters  act  on  that  sense  which 

I     produce  no  impression  upon  the  organs  of  taste  and  touch, — for  example, 
many  odorous  substances,  as  the  vapor  of  metals,  such  as  lead,  and  the^ 
vapor  of  many  minerals.     Some  volatile  substances,  however,  are  per- 
ceived not  only  by  the  sense  of  smell,  but  also  by  the  senses  of  touch  and 
taste.    Thus,  the  vapors  of  horse-radish  and  mustard,  and  acrid  suffoca- 

'l     ting  gases,  act  upon  the  conjunctiva  and  the  mucous  membrane  of  the 

;  Vol.  II.— 11. 


162 


HAND-BOOK  OF  PHYSIOLOGY. 


lungS;,  exciting,  through  the  common  sensory  nerves,  merely  modifications 
of  common  feeling;  and  at  the  same  time  they  excite  the  sensations  of 
smell  and  of  taste. 

Special  Sei^ses — Touch. 

Seat. — The  sense  of  touch  is  not  confined  to  particular  parts  of  the 
body  of  small  extent,  like  the  other  senses;  on  the  contrary,  all  parts  capa- 
ble of  perceiving  the  presence  of  a  stimulus  by  ordinary  sensation  are, 
in  certain  degrees,  the  seat  of  this  sense;  for  touch  is  simply  a  modifica- 
tion or  exaltation  of  common  sensation  or  sensibility.  The  nerves  on 
which  the  sense  of  touch  depends  are,  therefore,  the  same  as  those  which 
confer  ordinary  sensation  on  the  different  parts  of  the  body,  viz.,  those 
derived  from  the  posterior  roots  of  the  nerves  of  the  spinal  cord,  and  the 
sensory  cerebral  nerves. 

But,  although  all  pai'ts  of  the  body  supplied  with  sensory  nerves  are 
thus,  in  some  degree,  organs  of  touch,  yet  the  sense  is  exercised  in  per- 
fection only  in  those  parts  the  sensibility  of  which  is  extremely  delicate, 
e.g.,  the  skin,  the  tongue,  and  the  lips,  which  are  provided  with  abun- 
dant papillae.  A  peculiar  and,  of  its  own  kind  in  each  case,  a  very  acute 
sense  of  touch  is  exercised  through  the  medium  of  the  nails  and  teeth. 
To  a  less  extent,  the  hair  may  be  reckoned  an  organ  of  touch;  as  in  the 
case  of  the  eyelashes.  The  sense  of  touch  renders  us  conscious  of  the 
presence  of  a  stimulus,  from  the  slightest  to  the  most  intense  degree  of  its 
action,  by  that  indescribable  something  which  we  call  feeling,  or  com  Qion 
sensation.  The  modifications  of  this  sense  often  depend  on  the  extent 
of  the  parts  affected.  The  sensation  of  pricking,  for  example,  informs 
us  that  the  sensitive  particles  are  intensely  affected  in  a  small  extent; 
the  sensation  of  pressure  indicates  a  slighter  affection  of  the  parts  in  the 
greater  extent,  and  to  a  greater  depth.  It  is  by  the  depth  to  which  the 
parts  are  affected  that  the  feeling  of  pressure  is  distinguished  from  that 
of  mere  contact.  Schiff  and  Brown -Sequard  are  of  opinion  that  common 
sensibility  and  tactile  sensibility  manifest  themselves  to  the  individual  by 
the  aid  of  different  sets  of  fibres.  Sieveking  has  arrived  at  the  same  con- 
clusion from  pathological  observation. 

Varieties. — {a)  The  sense  of  fmich,  strictly  so-called  (tactile  sensi- 
bility), {!))  the  sense  of  pressure,  (c)  the  sense  of  temperature.  These 
when  carried  beyond  a  certain  degree  are  merged  in  {d)  the  sensation  of 
pain. 

Various  peculiar  sensations,  such  as  tichlivg,  must  be  classed  with 
pain  under  the  head  of  common  sensations,  since  they  give  us  no  infor- 
mation as  to  external  objects.  Such  sensations,  whether  pleasurable  or 
painful,  are  in  all  cases  referred  by  the  mind  to  the  part  affected,  and 
not  to  the  cause  which  stimulates  the  sensory  nerves  of  the  part.  The 


THE  SENSES. 


163 


sensation  of  tickling  may  be  produced  in  many  parts  of  the  body,  but 
with  especial  intensity  in  the  soles  of  the  feet.  Among  other  sensations 
belonging  to  this  class,  and  confined  to  particular  parts  of  the  body,  may 
be  mentioned  those  of  the  genital  organs  and  nipples. 

(a)  Touch  proper. — In  almost  all  parts  of  the  body  which  have 
delicate  tactile  sensibility  the  epidermis,  immediately  over  the  papillae,  is 
moderately  thin.  When  its  thickness  is  much  increased,  as  over  the  heel, 
the  sense  of  touch  is  very  much  dulled.  On  the  other  hand,  when  it  is 
altogether  removed,  and  the  cutis  laid  bare,  the  sensation  of  contact  is 
replaced  by  one  of  pain.  Further,  in  all  highly  sensitive  parts,  the 
papillae  are  numerous  and  highly  vascular,  and  usually  the  sensory  nerves 
are  connected  with  special  End-organs,  such  as  have  been  described 
(p.  337,  Vol.  L). 

The  acuteness  of  the  sense  of  touch  depends  very  largely  on  the  cuta- 
neous circulation,  •  which  is  of  course  largely  influenced  by  external 
temperature.  Hence  the  numbness,  familiar  to  every  one,  produced  by 
the  application  of  cold  to  the  skin. 

Special  organs  of  touch  are  present  in  most  animals,  among  which  may 
be  mentioned  the  antennae  of  insects,  the  "whiskers^^  (vibrissas)  of  cats 
and  other  carnivora,  the  wings  of  bats,  the  trunk  of  the  elephant,  and  the 
hand  of  man. 

Judgment  of  the  Form  and  Size  of  Bodies. — By  the  sense  of 
touch  the  mind  is  made  acquainted  with  the  size,  form,  and  other  external 
characters  of  bodies.  And  in  order  that  these  characters  may  be  easily 
ascertained,  the  sense  of  touch  is  especially  developed  in  those  parts  which 
can  be  readily  moved  over  the  surface  of  bodies.  Touch,  in  its  more 
limited  sense,  or  the  act  of  examining  a  body  by  the  touch,  consists  merely 
in  a  voluntary  employment  of  this  sense  combined  with  movement,  and 
stands  in  the  same  relation  to  the  sense  of  touch,  or  common  sensibility, 
generally,  as  the  act  of  seeking,  following,  or  examining  odors,  does  to 
the  sense  of  smell.  The  hand  is  best  adapted  for  it,  by  reason  of  its 
peculiarities  of  structure, — namely,  its  capability  of  pronation  and  supina- 
tion, which  enables  it,  by  the  movement  of  rotation,  to  examine  the  whole 
circumference  of  the  body;  the  power  it  possesses  of  opposing  the  thumb 
to  the  rest  of  the  hand,  and  the  relative  mobility  of  the  fingers;  and 
lastly  from  the  abundance  of  the  sensory  terminal  organs  which  it  pos- 
sesses. In  forming  a  conception  of  the  figure  and  extent  of  a  surface, 
the  mind  multiplies  the  size  of  the  hand  or  fingers  used  in  the  inquiry 
by  the  number  of  times  which  it  is  contained  in  the  surface  traversed; 
and  by  repeating  this  process  with  regard  to  the  different  dimensions  of  a 
solid  body,  acquires  a  notion  of  its  cubical  extent,  but,  of  course,  only 
an  imperfect  notion,  as  other  senses,  e.g.,  the  sight,  are  required  to  make 
it  complete. 


1G4 


HAND-BOOK  OF  PHYSIOLOGY. 


Acuteness  of  Touch. — The  perfection  of  the  sense  of  touch  on 
different  piirts  of  the  surface  is  proportioned  to  the  power  which  such 
parts  possess  of  distinguishing  and  isolating  the  sensations  produced  by 
two  points  phxced  close  together.  This  power  depends,  at  least  in  part, 
on  the  number  of  primitive  nerve-fibres  distributed  to  the  part;  for  the 
fewer  the  primitive  fibres  which  an  organ  receives,  the  more  likely  is  it 
that  several  impressions  on  different  contiguous  points  will  act  on  only 
one  nervous  fibre,  and  hence  be  confounded,  and  perhaps  produce  but 
one  sensation.  Experiments  have  been  made  to  determine  the  tactile  prop- 
erties of  different  parts  of  the  skin,  as  measured  by  this  power  of  distin- 
guishing distances.  These  consist  in  touching  the  skin,  while  the  eyes 
are  closed,  with  the  points  of  a  pair  of  compasses  sheathed  with  cork,  and 
in  ascertaining  how  close  the  points  of  compasses  might  be  brought  to 
each  other,  and  still  be  felt  as  two  bodies.    (E.  H.  Weber,  Valentin.) 

Table  of  variations  in  the  tactile  sensibility  of  different  parts. 

— Hie  measurement  indicates  the  least  distance  at  tvhicli  tlie  tiuo 
hlunted  points  of  a  pair  of  comp)asses  could  he  separately  distin- 
guislied,    (E.  H.  Weber.) 


Tip  of  tongue 

Palmar  surface  of  third  phalanx  of  forefinger 
Palmar  surface  of  second  phalanges  of  fingers 
Red  surface  of  under-lip 
Tip  of  the  nose  ..... 

Middle  of  dorsum  of  tongue  . 

Palm  of  hand  ...... 

Centre  of  hard  palate  .... 

Dorsal  surface  of  first  phalanges  of  fingers 

Back  of  hand  

Dorsum  of  foot  near  toes 

Gluteal  region  

Sacral  region  

Upper  and  lower  parts  of  forearm  . 
Back  of  neck  near  occiput 
Upper  dorsal  and  mid -lumbar  regions 
Middle  part  of  forearm  .... 

Middle  of  thigh  

Mid-cervical  region  .... 
Mid-dorsal  region  


^  inch 

i  " 
i 

H 

3 
2 

n 

u 

2i 


Moreover,  in  the  case  of  the  limbs,  it  was  found  that  before  they  were 
recognized  as  two,  the  points  of  the  compasses  had  to  further  separated 
when  the  line  joining  them  was  in  the  long  axis  of  the  limb,  than  when 
in  the  transverse  direction. 

According  to  Weber  the  mind  estimates  the  distance  between  two 
points  by  the  number  of  unexcited  nerve-endings  which  intervene  be- 
tween the  two  points  touched.    It  would  appear  that  a  certain  number 


THE  SENSES. 


165 


of  intervening  unexcited  nerve-eii dings  are  necessary  before  two  points 
touched  can  be  recognized  as  separate,  and  the  greater  this  number  the 
more  clearly  are  the  points  of  contact  distinguished  as  separate.  By 
practice  the  delicacy  of  a  sense  of  touch  may  be  very  much  increased. 
A  familiar  illustration  occurs  in  the  case  of  the  blind,  who,  by  constant 
practice,  can  acquire  the  power  of  reading  raised  letters  the  forms  of 
which  are  almost  if  not  quite  undistinguishable,  by  the  sense  of  touch, 
to  an  ordinary  person. 

The  power  of  correctly  localizing  sensations  of  touch  is  gradually 
derived  from  experience.  Tims  infants  when  in  pain  simply  cry,  but 
make  no  effort  to  remove  the  cause  of  irritation,  as  an  older  child  or  adult 
would,  doubtless  on  account  of  their  imperfect  knowledge  of  its  exact 
situation.  By  long  experience  this  power  of  localization  becomes  perfected, 
till  at  length  the  brain  possesses  a  complete  ''picture^"  as  it  were  of  the 
surface  of  the  body,  and  is  able  with  marvellous  exactness  to  localize  each 
sensation  of  touch. 

Illusions  of  Touch. — The  different  degrees  of  sensitiveness  pos-' 
sessed  by  different  parts  may  give  rise  to  errors  of  judgment  in  estimating 
the  distance  between  two  points  where  the  skin  is  touched.  Thus,  if 
blunted  points  of  a  pair  of  compasses  (maintained  at  a  constant  distance 
apart)  be  slowly  drawn  over  the  skin  of  the  cheek  toward  the  lips,  it  is 
almost  impossible  to  resist  the  conclusion  that  the  distance  between  the 
points  is  gradually  increasing.  When  they  reach  the  lips  they  seem  to 
be  considerably  further  apart  than  on  the  cheek.  Thus,  too,  our  estimate 
of  the  size  of  a  cavity  in  a  tooth  is  usually  exaggerated  when  based  upon 
sensation  derived  from  the  tongue  alone.  Another  curious  illusion  may 
here  be  mentioned.  If  we  close  the  eyes,  and  place  a  small  marble  or  pea 
between  the  crossed  fore  and  middle  fingers,  we  seem  to  be  touching  two 
marbles.  This  illusion  is  due  to  an  error  of  judgment.  The  marble  is 
touched  by  two  surfaces  which,  under  ordinary  circumstances,  could  only 
be  touched  by  two  separate  marbles,  hence  the  mind,  taking  no  cogni- 
zance of  the  fact  that  the  fingers  are  crossed,  forms  the  conclusion  that 
two  sensations  are  due  to  two  marbles. 

(b)  Pressure. — It  is  extremely  difficult  to  separate  touch  proper  from 
sensations  of  pressure,  and,  indeed,  the  former  may  be  said  to  depend  upon 
the  latter.  If  the  hand  be  rested  on  the  table  and  a  very  light  body  such 
as  a  small  card  placed  on  it,  the  only  sensation  produced  is  one  of  contact; 
if,  however,  an  ounce  weight  be  laid  on  the  card  an  additional  sensation 
(that  of  pressure)  is  experienced,  and  this  becomes  more  intense  as  the 
weight  is  increased.  If  now  the  weight  be  raised  by  the  hand,  we  are 
conscious  of  overcoming  a  certain  resistance;  this  consciousness  is  due 
to  what  is  termed  the  "muscular  sense''  (p.  119,  Vol.  II.).  The  estimate 
of  a  weight  is,  therefore,  usually  based  on  tiuo  sensations,  (1)  of  pressure  on 
the  skin,  and  (2)  the  muscular  sense. 


166 


HAND-BOOK  OF  PHYSIOLOGY. 


The  estimate  of  weight  derived  from  a  combination  of  these  two  sensa- 
tions (as  in  lifting  a  weight)  is  more  accurate  than  that  derived  from  the 
former  alone  (as  when  a  weight  is  laid  on  the  hand);  thus  AVeber  found 
that  b}^  the  former  method  he  could  generally  distinguish  19 1-  oz.  from 
20  oz.,  but  not  19f  oz.  from  20  oz.,  while  by  the  latter  he  could  at  most 
only  distinguish       oz.  from  15  oz. 

It  is  not  the  absolute,  but  the  relative,  amount  of  the  difference  of 
weight  which  we  have  thus  the  faculty  of  perceiving. 

It  is  not,  however,  certain,  that  our  idea  of  amount  of  muscular  force 
used  is  derived  solely  from  sensation  in  the  muscles.  We  have  the 
power  of  estimating  very  accurately  beforehand,  and  of  reg-ulating,  the 
amount  of  "nervous  influence  necessary  for  the  production  of  a  certain  de- 
gree of  movement.  When  we  raise  a  vessel,  with  the  contents  of  which 
we  are  not  acquainted,  the  force  we  employ  is  determined  by  the  idea  we 
have  conceived  of  its  weight.  If  it  should  happen  to  contain  some  very 
heavy  substance,  as  quicksilver,  we  shall  probably  let  it  fall;  the  amount 
of  muscular  action,  or  of  nervous  energy,  which  we  had  exerted  being  in- 
sufficient. The  same  thing  occurs  sometimes  to  a  person  descending  stairs 
in  the  dark;  he  makes  the  movement  for  the  descent  of  a  step  which  does 
not  exist.  It  is  possible  that  in  the  same  way  the  idea  of  weight  and 
pressure  in  raising  bodies,  or  in  resisting  forces,  may  in  part  arise  from 
a  consciousness  of  the  amount  of  nervous  energy  transmitted  from  the 
brain  rather  than  from  a  sensation  in  the  muscles  themselves.  The  men- 
tal conviction  of  the  inability  longer  to  support  a  weight  must  also  be 
distinguished  from  the  actual  sensation  of  fatigue  in  the  muscles. 

So,  with  regard  to  the  ideas  derived  from  sensations  of  touch  combined 
with  movements,  it  is  doubtful  how  far  the  consciousness  of  the  extent 
of  muscular  movement  is  obtained  from  sensations  in  the  muscles  them- 
selves. The  sensation  of  movement  attending  the  motions  of  the  hand  is 
very  slight;  and  persons  who  do  not  know  that  the  action  of  particular 
muscles  is  necessary  for  the  production  of  given  movements,  do  not  sus- 
pect that  the  movement  of  the  fingers,  for  example,  depends  on  an  action 
in  the  forearm.  The  mind  has,  nevertheless,  a  very  definite  knowledge 
of  the  changes  of  position  produced  by  movements;  and  it  is  on  this  that 
the  ideas  which  it  conceives  of  the  extension  and  form  of  a  body  are  in 
great  measure  founded. 

(c)  Temperature. — The  whole  surface  of  the  body  is  more  or  less 
sensitive  to  differences  of  temperature.  The  sensation  of  heat  is  distinct 
from  that  of  touch;  and  it  would  seem  reasonable  to  suppose  that  there 
are  special  nerves  and  nerve-endings  for  temperature.  At  any  rate  the 
poAver  of  discriminating  temperature  may  remain  unimpaired  when  the 
sense  of  touch  is  temporarily  in  abeyance.  Thus  if  the  ulnar  nerve  be 
compressed  at  the  elbow  till  the  sense  of  touch  is  very  much  dulled  in 
the  fingers  which  it  supplies,  the  sense  of  temperature  remains  quite 
unaffected  (Notlmagel). 

The  sensations  of  heat  and  cold  are  often  exceedingly  fallacious,  and 
in  many  cases  are  no  guide  at  all  to  the  absolute  temperature  as  indicated 


THE  SENSES. 


167 


by  a  thermometer.  All  that  we  can  with  safety  infer  from  our  sensations 
of  temperature,  is  that  a  given  object  is  warmer  or  cooler  than  the  skin. 
Thus  the  temperature  of  our  skin  is  the  standard;  and  as  this  varies  from 
hour  to  hour  according  to  the  activity  of  the  cutaneous  circulation,  onr 
estimate  of  the  absolute  temperature  of  any  body  must  necessarily  vary 
too.  If  we  put  the  left  hand  into  water  at  40°  F.  and  the  right  into  water 
at  110°  F.  and  then  immerse  both  in  water  at  80°  F.,  it  will  feel  warm  to 
the  left  hand  but  cool  to  the  right.  Again,  a  piece  of  metal  which  has 
really  the  same  temperature  as  a  given  piece  of  wood  will  feel  much 
colder,  since  it  conducts  away  the  heat  much  more  rapidly.  For  the 
same  reason  air  in  motion  feels  very  much  cooler  than  air  of  the  same 
temperature  at  rest. 

Perhaps  the  most  striking  example  of  the  fallaciousness  of  our  sensa- 
tions as  a  measure  of  temperature  is  afforded  by  fever.  In  a  shivering  fit 
of  ague  the  patient  feels  excessively  cold,  whereas  his  actual  temperature 
is  several  degrees  above  the  normal,  while  in  the  sweating  stage  which 
succeeds  it  he  fefels  very  warm,  whereas  really  his  temperature  has  fallen 
several  degrees.  In  the  former  case  the  cutaneous  circulation  is  much 
diminished,  in  the  latter  much  increased;  hence  the  sensations  of  cold  and 
heat  respectively. 

In  some  cases  we  are  able  to  form  a  fairly  accurate  estimate  of  absolute 
temperature.  Thus,  by  plunging  the  elbow  into  a  bath,  a  practised  bath- 
attendant  can  tell  the  temperature  sometimes  within  1°  F. 

The  temperatures  which  can  be  readily  discriminated  are  between 
50° — 115°  F.  (10° — 45^  C);  very  low  and  very  high  temperature  alike 
produce  a  burning  sensation.  A  temperature  appears  higher  according 
to  the  extent  of  cutaneous  surface  exposed  to  it.  Thus,  water  of  a  tem- 
perature which  can  be  readily  borne  by  the  hand,  is  quite  intolerable  if 
the  whole  body  be  immersed.  So,  too,  water  appears  much  hotter  to  the 
hand  than  to  a  single  finger. 

The  delicacy  of  the  sense  of  temperature  coincides  in  the  main  with 
that  of  touch,  and  appears  to  depend  largely  on  the  thickness  of  the  skin; 
hence,  in  the  elbow  where  the  skin  is  thin,  the  sense  of  temperature  is 
delicate,  though  that  of  touch  is  not  remarkably  so.  Weber  has  further 
ascertained  the  following  facts:  two  compass  points  so  near  together  on 
the  skin  that  they  produce  but  a  single  impression,  at  once  give  rise  to 
two  sensations,  when  one  is  hotter  than  the  other.  Moreover,  of  two 
bodies  of  equal  weight,  that  which  is  the  colder  feels  heavier  than  the 
other. 

As  every  sensation  is  attended  with  an  idea,  and  leaves  behind  it  an 
idea  in  the  mind  which  can  be  reproduced  at  will,  we  are  enabled  to  com- 
pare the  idea  of  a  past  sensation  with  another  sensation  really  present. 
Thus  we  can  compare  the  weight  of  one  body  with  another  which  we  had 
previously  felt,  of  which  the  idea  is  retained  in  our  mind.    Weber  was 


168 


HAND-BOOK  OF  PHYSIOLOGY. 


indeed  able  to  distinguish  in  this  manner  between  temperatures,  experi- 
enced one  after  the  other,  better  than  between  temperatures  to  which  the 
two  hands  were  simultaneously  subjected.  This  power  of  comparing 
present  with  past  sensations  diminishes,  however,  in  proportion  to  the 
time  which  has  elapsed  between  them.  After-sensations  left  by  impres- 
sions on  nerves  of  common  sensibility  or  touch  are  very  vivid  and  durable. 
As  long  as  the  condition  into  which  the  stimulus  has  thrown  the  organ 
endures,  the  sensation  also  remains,  though  the  exciting  cause  should  have 
long  ceased  to  act.  Both  painful  and  pleasurable  sensations  afford  many 
examples  of  this  fact. 

Subjective  sensations,  or  sensations  dependent  on  internal  causes, 
are  in  no  sense  more  frequent  than  in  the  sense  of  touch.  All  the  sensa- 
tions of  pleasure  and  pain,  of  heat  and  cold,  of  lightness  and  weight,  of 
fatigue,  etc.,  may  be  produced  by  internal  causes.  Neuralgic  pains,  the 
sensation  of  rigor,  formication  or  the  creeping  of  ants,  and  the  states  of 
the  sexual  organs  occurring  during  sleep,  afford  striking  exjimples  of  sub- 
jective sensations.  The  mind  has  a  remarkable  power  bf  exciting  sensa- 
tions in  the  nerves  of  common  sensibility;  just  as  the  thought  of  the  nau- 
seous excites  sometimes  the  sensation  of  nausea,  so  the  idea  of  pain  gives 
rise  to  the  actual  sensation  of  pain  in  a  part  predisposed  to  it;  numerous 
examples  of  this  influence  might  be  quoted. 

Taste. 

Conditions  Necessary. — The  conditions  for  the  perceptions  of  taste 
are: — 1,  the  presence  of  a  nerve  and  nerve-centre  with  special  endow- 
ments; 2,  the  excitation  of  the  nerve  by  the  sapid  matters,  which  for  this 
purpose  must  be  in  a  state  of  solution.  The  nerves  concerned  in  the  pro- 
duction of  the  sense  of  taste  have  been  already  considered  (pp.  142  and  146, 
Vol.  II.).  The  mode  of  action  of  the  substances  which  excite  taste  con- 
sists in  the  production  of  a  change  in  the  condition  of  the  gustatory  nerves, 
and  the  conduction  of  the  stimulus  thus  produced  to  the  nerve-centre; 
and,  according  to  the  difference  of  the  substances,  an  infinite  variety  of 
changes  of  condition  of  the  nerves,  and  consequently  of  stimulations  of 
the  gustatory  centre,  may  be  induced.  The  matters  to  be  tasted  must 
either  be  in  solution  or  be  soluble  in  the  moisture  covering  the  tongue; 
hence  insoluble  substances  are  usually  tasteless,  and  produce  merely  sen- 
sations of  touch.  Moreover,  for  the  perfect  action  of  a  sapid,  as  of  an 
odorous  substance,  it  is  necessary  that  the  sentient  surface  should  be 
moist.  Hence,  when  the  tongue  and  fauces  are  dry,  sapid  substances, 
€vcn  in  solution,  are  with  difficulty  tasted. 

The  TKirvcs  of  taste,  like  the  nerves  of  other  s])ocial  senses,  may  liave 
their  peculiar  proi)erties  excited  by  various  other  kinds  of  irritation,  such 


THE  SENSES. 


169 


as  electricity  and  mechanical  impressions.  Thus,  Henle  observed  that  a 
small  current  of  air  directed  upon  the  tongue  gives  rise  to  a  cool  saline 
taste,  like  that  of  saltpetre;  and  Baly  has  shown  that  a  distinct  sensation 
of  taste,  similar  to  that  caused  by  electricity,  may  be  produced  by  a  smart 
tap  applied  to  the  papillae  of  the  tongue.  Moreover,  the  mechanical  irri- 
tation of  the  fauces  and  palate  produces  the  sensation  of  nausea,  which  is 
probably  only  a  modification  of  taste. 

Seat  of  Sensation. — The  principal  seat  of  the  sense  of  taste  is  the 
tongue.  But  the  results  of  experiments  as  well  as  ordinary  experience 
show  that  the  soft  palate  and  its  arches,  the  uvula,  tonsils,  and  probably 
the  upper  part  of  the  pharynx,  are  endowed  with  taste.  These  parts, 
together  with  the  base  and  posterior  parts  of  the  tongue,  are  supplied 
with  branches  of  the  glosso-pharyngeal  nerve,  and  evidence  has  been 
already  adduced  that  the  sense  of  taste  is  conferred  upon  them  by  this 
nerve.  In  most,  though  not  in  all  persons,  the  anterior  parts  of  the 
tongue,  especially  the  edges  and  tip,  are  endowed  with  the  sense  of  taste. 
The  middle  of  the  dorsum  is  only  feebly  endowed  with  this  sense,  prob- 
ably because  of  the  density  and  thickness  of  the  epithelium  covering  the 
filiform  papillae  of  this  part  of  the  tongue,  which  will  prevent  the  sapid 
substances  from  penetrating  to  their  sensitive  parts.  The  gustatory  prop- 
erty of  the  anterior  part  of  the  tongue  is  due,  as  already  said  (p.  142, 
Vol.  II.),  to  the  lingual  or  gustatory  branch  of  the  fifth  nerve. 

Structure  of  the  Tongue. — The  tongue  is  a  muscular  organ  covered 
by  mucous  membrane.  The  muscles,  which  form  the  greater  part  of  the 
substance  of  the  tongue  (i7itrinsic  muscles)  are  termed  Unguales;  and 
by  these,  which  are  attached  to  the  mucous  membrane  chiefly,  its  smaller 
and  more  delicate  movements  are  chiefly  performed. 

By  other  muscles  {extrinsic  muscles)  as  the  genio-hyoglossus,  the 
styloglossus,  etc.,  the  tongue  is  fixed  to  surrounding  parts;  and  by  this 
group  of  muscles  its  larger  movements  are  performed. 

The  mucous  membrane  of  the  tongue  resembles  other  mucous  mem- 
branes (p.  322,  Vol.  I.)  in  essential  points  of  structure,  but  contains 
papillce,  more  or  less  peculiar  to  itself;  peculiar,  however,  in  details  of 
structure  and  arrangement,  not  in  their  nature.  The  tongue  is  beset  with 
numerous  mucous  follicles  and  glands.  The  use  of  the  tongue  in  relation 
to  mastication  and  deglutition  has  already  been  considered  (pp.  226  and 
238,  Vol.  L). 

The  larger  papillcB  of  the  tongue  are  thickly  set  over  the  anterior  two- 
thirds  of  its  upper  surface,  or  dorsum  (Fig.  349),  and  give  to  it  its  char- 
acteristic roughness.  In  carnivorous  animals,  especially  those  of  the  cat 
tribe,  the  papillae  attain  a  large  size,  and  are  developed  into  sharp  re- 
curved horny  spines.  Such  papillae  cannot  be  regarded  as  sensitive,  but 
they  enable  the  tongue  to  play  the  part  of  a  most  efficient  rasp,  as  in 
scraping  bones,  or  of  a  comb  in  cleaning  their  fur.   Their  greater  promi- 


170 


HAND-BOOK  OF  PHYSIOLOGY. 


nence  than  those  of  the  skin  is  due  to  their  interspaces  not  being  filled 
up  with  epithelium,  as  the  interspaces  of  the  papillae  of  the  skin  are. 
The  papillae  of  the  tongue  present  several  diversities  of  form;  but  three 
principal  varieties,  differing  both  in  seat  and  general  characters^  may 
usually  be  distinguished,  namely,  the  (1)  circumvallate,  the  (2)  fungi- 
form, and  the  (3)  Uliform  papillae.    Essentially  these  have  all  of  them 


Fig.  349.— Papillar  surface  of  the  tonfrxic.  with  the  fauces  and  tonsils.  1, 1,  circumvallate  papil- 
lae, in  front  of  2,  the  foramen  caecum;  3.  fuuf^ifoi  iii  i)apilla?;  4,  fiHform  and  conical  papillae;  5,  trans- 
verse and  oblique  rugae;  6,  mucous  glands  at  the  base  of  the  tongue  and  in  the  fauces;  7,  tonsils;  8, 
part  of  the  epiglottis;  9,  median  glosso-epiglottidean  fold  (fraenum  epiglottidis).    (From  Sappey.) 

the  same  structure,  that  is  to  say,  they  are  all  formed  by  a  projection  of 
the  mucous  membrane,  and  contain  special  branches  of  blood-vessels  and 
nerves.  In  details  of  structure,  however,  they  differ  considerably  one 
from  another. 

The  surface  of  each  kind  is  studded  by  minute  conical  processes  of 
mucous  membrane,  wliich  tlius  form  secondary  })apilla3. 


THE  SENSES. 


171 


Simple  papillae  also  occur  over  most  other  parts  of  the  tongue  not 
occupied  by  the  compound  papillae,  and  extend  for  some  distance  behind 
the  papillae  circumvallatae.  The  mucous  membrane  immediately  in  front 
of  the  epiglottis  is,  however,  free  from  them.  They  are  commonly  buried 
beneath  the  epithelium;  hence  they  are  often  overlooked. 

(1.)  Circiimvallate. — These  papillae  (Fig.  350),  eight  or  ten  in  num- 
ber, are  situate  in  two  V-shaped  lines  at  the  base  of  the  tongue  (1,  1, 


Fig.  350.— Vertical  section  of  a  circumvallate  papilla  10  1.— A,  the  papillae;  B,  the  surrounding 
wall;  a,  the  epithehal  covering;  6,  the  nerves  of  the  papilla  and  wall  spreading  tovs^ard  the  surfaces 
c,  the  secondary  papillae.  (Kolhker.) 

Fig.  349).  They  are  circular  elevations  from  yV^^  of  an  inch  wide, 
each  with  a  central  depression,  and  surrounded  by  a  circular  fissure,  at 
the  outside  of  which  again  is  a  slightly  elevated  ring,  both  the  central 
elevation  and  the  ring  being  formed  of  close  set  simple  papillae  (Fig.  350). 

(2.)  Fungiform. — The  fungiform  papillae  (3,  Fig.  349)  are  scattered 
chiefly  over  the  sides  and  tip,  and  sparingly  over  the  middle  of  the  dor- 
sum, of  the  tongue;  their  name  is  derived  from  their  being  usually  nar- 


FiG.  351.— Surface  and  section  of  the  fungiform  papillas.  A,  the  surface  of  a  fungiform  papilla, 
partially  denuded  of  its  epithelium;  p,  secondary  papillae;  e,  epithelium.  B,  section  of  a  fungiform 
papula  with  the  blood-vessels  injected;  a,  artery;  vein;  c,  capillary  loops  of  similar  papillas  in  the 
neighboring  structure  of  the  tongue;  d,  capillary  loops  of  the  secondary  papillae;  e,  epithelium. 
(From  KoUiker,  after  Todd  and  Bowman.) 

rower  at  their  base  than  at  their  summit.  They  also  consist  of  groups  of 
simple  papillae  (A,  Fig.  351),  each  of  which  contains  in  its  interior  a  loop 
of  capillary  blood-vessels  (B),  and  a  nerve-fibre. 

(3.)  Conical  or  Filiform. — These,  which  are  the  most  abundant 
papillae,  are  scattered  over  the  whole  surface  of  the  tongue,  but  especially 
over  the  middle  of  the  dorsum  (Fig.  349).  They  vary  in  shape  some- 
what, but  for  the  most  part  are  conical  or  filiform,  and  covered  by  a  thick 


172 


HAND-BOOK  OF  PHYSIOLOGY. 


layer  of  epidermis,  which  is  arranged  over  them,  either  in  an  imbricated 
manner,  or  is  prolonged  from  their  surface  in  the  form  of  fine  stiff  pro- 
jections, hair-like  in  appearance,  and  in  some  instances  in  structure  also 
(Fig.  352).  From  their  peculiar  structure,  it  seems  likely  that  these 
papillae  have  a  mechanical  function,  or  one  allied  to  that  of  touch  rather 
than  of  taste;  the  latter  sense  being  probably  seated  especially  in  the 
ther  two  varieties  of  papillae,  the  circumvallate  and  the  fungiform. 
The  epitheliufn  of  the  tongue  is  stratified  with  the  upper  layers  of  the 


Fig.  352.— Two  filiform  papillse,  one  with  epithelium,  the  other  without.  35-1.— p,  the  substance 
of  the  papillae  dividing  at  their  vipper  extremities  into  secondary  papillae;  a,  artery,  and  v,  vein, 
dividing  into  capillary  loops ;  e,  epithelial  covering,  laminated  between  the  papillae,  but  extended 
into  hair-like  processes,  /,  from  the  extremities  of  the  secondary  papillas.  (From  KolUker,  after 
Todd  and  Bowman.) 

squamous  kind.  It  covers  every  part  of  the  surface;  but  over  the  fungi- 
form papillae  forms  a  thinner  layer  than  elsewhere.  The  epithelium  cover- 
ing the  filiform  papillae  is  extremely  dense  and  thick,  and,  as  before  men- 
tioned, projects  from  their  sides  and  summits  in  the  form  of  long,  stiff, 
hair-like  processes  (Fig.  352).  Many  of  these  processes  bear  a  close  re- 
semblance to  hairs.  Blood-vessels  and  nerves  are  supplied  freely  to  the 
papillae.  The  nerves  in  the  fungiform  and  circumvallate  papillee  form  a 
kind  of  ])loxus,  spreading  out  brusli-wise  (Fig.  350),  but  tlie  exact  mode 
of  termination  of  the  nerve-filaments  is  not  certainly  known. 


THE  SENSES. 


173 


Taste  Ooblets. — In  the  circumvallate  papillae  of  the  tongue  of  man 
peculiar  structures  known  as  gustatory  huds  or  taste  gohlets,  have  been 
discovered  (Loven,  Schwalbe).  They  are  of  an  oval  shape,  and  consist  of 
a  number  of  closely  packed,  very  narrow  and  fusiform,  cells  {gustatory 
cells).  This  central  core  of  gustatory  cells  is  enclosed  in  a  single  layer  of 
broader  fusiform  cells  (encasing  cells).  The  gustatory  cells  terminate  in 
fine  spikes  not  unlike  cilia,  which  project  on  the  free  surface  (Fig.  353). 

These  bodies  also  occur  side  by  side  in  considerable  numbers  in  the 


Fig.  353.— Taste-goblet  from  dog's  epiglottis  (laryngeal  surface  near  the  base),  precisely  similar 
in  structure  to  those  found  in  the  tongue,  a,  depression  in  epithelium  over  goblet;  below  the  letter 
are  seen  the  fine  hair-like  processes  in  which  the  cells  terminate;  c,  two  nuclei  of  the  axial  (gustatory) 
cells.  The  more  superficial  nuclei  belong  to  the  superficial  (encasing)  cells;  the  converging  lines  in- 
dicate the  fusiform  shape  of  the  encasing  cells.    X  400.  (Schofleld.) 

epithelium  of  the  papilla  f  oliata,  which  is  situated  near  the  root  of  the 
tongue  in  the  rabbit,  and  also  in  man.  Similar  "taste-goblets''^  also  occur 
pretty  evenly  distributed  on  the  posterior  (laryngeal)  surface  of  the  epi- 
glottis (Verson,  Schofield).  It  seems  probable,  from  their  distribution, 
that  all  these  so-called  taste-goblets  are  gustatory  in  function,  though 
no  nerves  have  been  distinctly  traced  into  them. 

Other  Functions  of  the  Tongue. — Besides  the  sense  of  taste,  the 
tongue,  by  means  also  of  its  papillae,  is  endued,  (2)  especially  at  its  sides 
and  tip,  with  a  very  delicate  and  accurate  sense  of  touch  (p.  164,  Vol. 
II.),  which  renders  it  sensible  of  the  impressions  of  heat  and  cold,  pain 
and  mechancial  pressure,  and  consequently  of  the  form  of  surfaces.  The 
tongue  may  lose  its  common  sensibility,  and  still  retain  the  sense  of  taste, 
and  vice  versa.  This  fact  renders  it  probable  that,  although  the  senses 
of  taste  and  of  touch  may  be  exercised  by  the  same  papillae  supplied  by 
the  same  nerves,  yet  the  nervous  conductors  for  these  two  different  sen- 
sations are  distinct,  just  as  the  nerves  for  smell  and  common  sensibility 
in  the  nostrils  are  distinct;  and  it  is  quite  conceivable  that  the  same 
nervous  trunk  may  contain  fibres  differing  essentially  in  their  specific 
properties.  Facts  already  detailed  (p.  142,  Vol.  II.)  seem  to  prove  that 
the  lingual  branch  of  the  fifth  nerve  is  the  conductor  of  sensations  of 
taste  in  the  anterior  part  of  the  tongue;  and  it  is  also  certain,  from  the 


174  HAND-BOOK  OF  PHYSIOLOGY. 

marked  manifestations  of  pain  to  which  its  division  in  animals  gives  rise, 
that  it  is  likewise  a  nerve  of  common  sensibility.  The  glosso-pharyngeal 
also  seems  to  contain  fibres  both  of  common  sensation  and  of  the  special 
sense  of  taste. 

The  functions  of  the  tongue  in  connection  with  (3)  speech,  (4)  masti- 
tication,  (5)  deglutition,  (6)  suction,  have  been  referred  to  in  other 
chapters. 

Taste  and  Smell;  Perceptions. — The  concurrence  of  common 
and  special  sensibility  in  the  same  part  makes  it  sometimes  difficult  to 
determine  whether  the  impression  produced  by  a  substance  is  perceived 
through  the  ordinary  sensitive  fibres,  or  through  those  of  the  sense  of 
taste.  In  many  cases,  indeed,  it  is  probable  that  both  sets  of  nerve-fibres 
are  concerned,  as  when  irritating  acrid  substances  are  introduced  into  the 
mouth. 

Much  of  the  perfection  of  the  sense  of  taste  is  often  due  to  the  sapid 
substances  being  also  odorous,  and  exciting  the  simultaneous  action  of 
the  sense  of  smell.  This  is  shown  by  the  imperfection  of  the  taste  of 
such  substances  when  their  action  on  the  olfactory  nerves  is  prevented  by 
closing  the  nostrils.  Many  fine  wines  lose  much  of  their  apparent  excel- 
lence if  the  nostrils  are  held  close  while  they  are  drunk. 

Varieties  of  Tastes. — Among  the  most  clearly  defined  tastes  are 
the  sweet  and  bitter  (which  are  more  or  less  opposed  to  each  other),  the 
acid,  alkaline,  and  saline  tastes.  Acid  and  alkaline  taste  may  be  excited 
by  electricity.  If  a  piece  of  zinc  be  placed  beneath  and  a  piece  of  copper 
above  the  tongue,  and  their  ends  brought  into  contact,  an  acid  taste  (due 
to  the  feeble  galvanic  current)  is  produced.  The  delicacy  of  the  sense  of 
taste  is  sufficient  to  discern  1  part  of  sulphuric  acid  in  1000  of  water;  but 
it  is  far  surpassed  in  acuteness  by  the  sense  of  smell. 

A  fter-tastes. — Very  distinct  sensations  of  taste  are  frequently  left  after 
the  substances  which  excited  them  have  ceased  to  act  on  the  nerve;  and 
such  sensations  often  endure  for  a  long  time,  and  modify  the  taste  of 
other  substances  applied  to  the  tongue  afterward.  Thus,  the  taste  of  sweet 
substances  spoils  the  flavor  of  wine,  the  taste  of  cheese  improves  it.  There 
appears,  therefore,  to  exist  the  same  relation  between  tastes  as  between 
colors,  of  which  those  that  are  opposed  or  complementary  render  each 
other  more  vivid,  though  no  general  principles  governing  this  relation  have 
been  discovered  in  the  case  of  tastes.  In  the  art  of  cooking,  however,  at- 
tention has  at  all  times  been  paid  to  the  consonance  or  harmony  of  flavors 
in  their  combination  or  order  of  succession,  just  as  in  painting  and  music 
the  fundamental  principles  of  liarmony  have  been  employed  empirically 
while  the  theoretical  laws  were  unknown. 

Frequent. and  continued  repetitions  of  the  same  taste  render  the  per- 
ception of  it  less  and  loss  distinct,  in  tlio  same  way  tliat  a  color  becomes 
more  and  more  dull  and  indistinct  the  longer  the  eye  is  fixed  upon  it. 


THE  SENSES. 


175 


Thus,  after  frequently  tasting  first  one  and  then  the  other  of  two  kinds 
of  wine,  it  becomes  impossible  to  discriminate  between  them. 

The  simple  contact  of  a  sapid  substance  with  the  surface  of  the  gustatory 
organ  seldom  gives  rise  to  a  distinct  sensation  of  taste;  it  needs  to  be  dif- 
fused over  the  surface,  and  brought  into  intimate  contact  with  the  sensi- 
tive parts  by  compression,  friction,  and  motion  between  the  tongue  and 
palate. 

Subjective  Sensations  of  Taste. — The  sense  of  taste  seems  capa- 
ble of  being  excited  only  by  external  causes,  such  as  changes  in  the  con- 
ditions of  the  nerves  or  nerve-centres,  produced  by  congestion  or  other 
causes,  which  excite  subjective  sensations  in  the  other  organs  of  sense. 
But  little  is  known  of  the  subjective  sensations  of  taste;  for  it  is  difficult 
to  distinguish  the  phenomena  from  the  effects  of  external  causes,  such 
as  changes  in  the  nature  of  the  secretions  of  the  mouth. 

Smell. 

Conditions  Necessary. — (1.)  The  first  conditions  essential  to  the 
sense  of  smell  are  a  special  nerve  and  nerve-centre,  the  changes  in  whose 
condition  are  perceived  in  sensations  of  odor;  for  no  other  nervous  struc- 
ture is  capable  of  these  sensations,  even  though  acted  on  by  the  same 
causes.  The  same  substance  which  excites  the  sensation  of  smell  in  the 
olfactory  centre  may  cause  another  peculiar  sensation  through  the  nerves 
of  taste,  and  may  produce  an  irritating  and  burning  sensation  on  the  nerves 
of  touch;  but  the  sensation  of  odor  is  yet  separate  and  distinct  from  these, 
though  it  may  be  simultaneously  perceived.  (2.)  The  second  condition 
of  smell  is  a  peculiar  change  produced  in  the  olfactory  nerve  and 
its  centre  by  the  stimulus  or  odorous  substance.  (3.)  The  material 
causes  of  odors  are,  usually,  in  the  case  of  animals  living  in  the  air, 
either  solids  suspended  in  a  state  of  extremely  fine  division  in  the 
atmosphere;  or  gaseous  exhalations  often  of  so  subtile  a  nature  that  they 
can  be  detected  by  no  other  re-agent  than  the  sense  of  smell  itself.  The 
matters  of  odor  must,  in  all  cases,  be  dissolved  in  the  mucus  of  the  mucous 
membrane  before  they  can  be  immediately  applied  to,  or  affect  the  olfac- 
tory nerves;  therefore  a  further  condition  necessary  for  the  perception  of 
odors  is,  that  the  mucous  membrane  of  the  nasal  cavity  be  moist.  When 
the  Schneiderian  membrane  is  dry,  the  sense  of  smell  is  impaired  or  lost;  in 
the  first  stage  of  catarrh,  when  the  secretion  of  mucus  within  the  nostrils 
IS  lessened,  the  faculty  of  perceiving  odor  is  either  lost  or  rendered  very 
imperfect.  (4.)  In  animals  living  in  the  air,  it  is  also  requisite  that  the 
odorous  matter  should  be  transmitted  in  a  current  through  the  nostrils. 
This  is  effected  by  an  inspiratory  movement,  the  mouth  being  closed; 
hence  we  have  voluntary  influence  over  the  sense  of  smell;  for  by  inter- 
rupting respiration  we  prevent  the  perception  of  odors,  and  by  repeated 


176 


HAND-BOOK  OF  PHYSIOLOGY. 


quick  inspiration,  assisted,  as  in  the  act  of  sniffing,  by  the  action  of  the 
nostrils,  we  render  the  impression  more  intense  (see  p.  201,  Vol.  I.).  An 
odorous  substance  in  a  liquid  form  injected  into  the  nostrils  appears  in- 
capable of  giving  rise  to  the  sensation  of  smell:  thus  Weber  could  not 
smell  the  slightest  odor  when  his  nostrils  were  completely  filled  with 
water  containing  a  large  quantity  of  eau  de  Cologne. 

Seat  of  the  Sense  of  Smell. — The  human  organ  of  smell  is  formed 
by  the  filaments  of  the  olfactory  nerves,  distributed  in  the  mucous  mem- 
brane covering  the  upper  third  of  the  septum  of  the  nose,  the  superior 
turbinated  or  spongy  bone,  the  upper  part  of  the  middle  turbinated  bone, 
and  the  upper  w^l  of  the  nasal  cavities  beneath  the  cribriform  plates  of 
the  ethmoid  bones  (Figs.  354  and  355).    The  olfactory  region  is  covered 


Fig.  354.— Nerves  of  the  septum  nasi,  seen  from  the  right  side.  the  olfactory  bulb;  1,  the 

olfactory  nerves  passing  through  the  foramina  of  the  cribriform  plate,  and  descending  to  be  chs- 
tributed  on  the  septum;  2,  the  internal  or  septal  twig  of  the  nasal  branch  of  the  ophthalmic  nerve;  3, 
naso-palatine  nerves.   (From  Sappey,  after  Hirschfeld  and  Leveill6.) 

by  cells  of  cyli7idrical  epithelium,  prolonged  at  their  deep  extremities 
into  fine  branched  processes,  but  not  ciliated;  and  interspersed  with  these 
are  fusiform  (olfactory)  cells,  with  ^both  superficial  and  deep  processes 
(Fig.  356),  the  latter  being  probably  connected  with  the  terminal  fila- 
ments of  the  olfactory  nerve.  The  lower,  or  respiratory  part,  as  it  is 
called,  of  the  nasal  fossas  is  lined  by  cylmdrical  ciliated  epithelium,  ex- 
cept in  the  region  of  the  nostrils,  where  it  is  sqiianwus.  The  branches 
of  the  olfactory  nerves  retain  much  of  the  same  soft  and  greyish  texture 
which  distinguishes  those  of  the  olfactory  tracts  within  the  cranium. 
Their  filaments,  also,  are  peculiar,  more  resembling  those  of  the  sympa- 
thetic nerve  than  the  filaments  of  the  other  cerebral  nerves  do,  contain- 
ing no  outer  white  substance,  and  being  finely  granular  and  nucleated. 
Tlie  sense  of  smell  is  derived  exclusively  through  those  parts  of  the  nasal 
cavities  in  which  the  olfactory  nerves  are  distributed;  the  accessory  cavi- 
ties or  sinuses  communicating  with  the  nostrils  seem  to  have  no  relation 


THE  SENSES. 


177 


to  it.  Air  impregnated  with  the  vapor  of  camphor  was  injected  into  the 
frontal  sinus  through  a  fistulous  opening,  and  odorous  substances  have 
been  injected  into  the  antrum  of  Highmore;  but  in  neither  case  was  any 
odor  perceived  b}^  the  patient.  The  purposes  of  these  sinuses  appear  to 
be,  that  the  bones,  necessarily  large  for  the  action  of  the  muscles  and  other 
parts  connected  with  them,  may  be  as  light  as  possible,  and  that  there 
may  be  more  room  for  the  resonance  of  the  air  in  vocalizing.  The  former 


Fig.  355.— Nerves  of  the  outer  walls  of  the  nasal  fossae.  3-5.— 1,  network  of  the  branches  of  the 
olfactory  nerve,  descending  upon  the  region  of  the  superior  and  middle  turbinated  bones;  2,  external 
twig  of  the  ethmoidal  branch  of  the  nasal  nerves;  3,  spheno-palatine  ganglion;  4,  ramification  of  the 
anterior  palatine  nerves;  5,  posterior,  and  6,  middle  divisions  of  the  palatine  nerves;  7,  branch  to  the 
region  of  the  inferior  turbinated  bone;  8,  branch  to  the  region  of  the  superior  and  middle  turbinated 
bones;  9,  naso-palatine  branch  to  the  septum  cut  short.  (From  Sappey,  after  Hirschfeld  and 
Leveill6.) 

purpose,  which  is  in  other  bones  obtained  by  filling  their  cavities  with 
fat,  is  here  attained,  as  it  is  in  many  bones  of  birds,  by  their  being  filled 
with  air. 

Other  Functions  of  the  Olfactory  Region. — All  parts  of  the  nasal 
cavities,  whether  or  not  they  can  be  the  seat  of  the  sense  of  smell,  are 
endowed  with  common  sensibility  by  the  nasal  branches  of  the  first  and 
second  divisions  of  the  fifth  nerve.  Hence  the  sensations  of  cold,  heat, 
itching,  tickling,  and  pain;  and  the  sensation  of  tension  or  pressure  in  the 
nostrils.  That  these  nerves  cannot  perform  the  function  of  the  olfactory 
nerves  is  proved  by  cases  in  which  the  sense  of  smell  is  lost,  while  the  mu- 
cous membrane  of  the  nose  remains  susceptible  of  the  various  modifications 
of  common  sensation  or  touch.  But  it  is  often  difficult  to  distinguish  the 
sensation  of  smell  from  that  of  mere  feeling,  and  to  ascertain  what  belongs^ 
to  each  separately.  This  is  the  case  particularly  with  the  sensations: 
excited  in  the  nose  by  acrid  vapors,  as  of  ammonia,  horse-radish,  mustard,, 
etc.,  which  resemble  much  the  sensations  of  the  nerves  of  touch;  and  the 
difficulty  is  the  greater,  when  it  is  remembered  that  these  acrid  vapors 
Vol.  II.— 13. 


178 


ha:^^d-book  of  physiology. 


have  nearly  the  same  action  upon  the  mucous  membrane  of  tlie  eyelids. 
It  was  because  the  common  sensibility  of  the  nose  to  these  irritating  sub- 
stances remained  after  the  destruction  of  the  olfactory  nerves,  that  Magen- 
die  was  led  to  the  erroneous  belief  that  the  fifth  nerve  might  exercise  this 
special  sense. 

Varieties  of  Odorous  Sensations. — Animals  do  not  all  equally 
perceive  the  same  odors;  the  odors  most  plainly  perceived  by  an  herbiv- 
orous animal  and  by  a  carnivorous  animal  are  dilferent.  The  Carnivora 
have  the  power  of  detecting  most  accurately  by  the  smell 
the  special  peculiarities  of  animal  matters,  and  of  tracking 
other  animals  by  the  scent;  but  have  apparently  very  lit- 
tle sensibility  to  the  odors  of  plants  and  flowers.  Herbiv- 
orous animals  are  peculiarly  sensitive  to  the  latter,  and 
have  a  narrower  sensibility  to  animal  odors,  especially  to 
such  as  proceed  from  other  individuals  than  their  own 
species.  Man  is  far  inferior  to  many  animals  of  both 
classes  in  respect  of  the  acuteness  of  smell;  but  his  sphere 
of  susceptibility  to  various  odors  is  more  uniform  and  ex- 
tended. The  cause  of  this  difference  lies  probably  in  the 
endowments  of  the  cerebral  parts  of  the  olfactory  appa- 
ratus. The  delicacy  of  the  sense  of  smell  is  most  remark- 
able; it  can  discern  the  presence  of  bodies  in  quantities 
so  minute  as  to  be  undiscoverable  even  by  spectrum  an- 
alysis; TFo,oTo-,oTo-  ^  grain  of  musk  can  be  distinctly 
smelt  (Valentin).  Opposed  to  the  sensation  of  an  agree- 
able odor  is  that  of  a  disagreeable  or  disgusting  odor, 
which  corresponds  to  the  sensations  of  pain,  dazzling  and 
disharmony  of  colors,  and  dissonance  in  the  other  senses. 
The  cause  of  this  difference  in  the  effect  of  different 
odors  is  unknown:  but  this  much  is  certain,  that  odors  are 
pleasant  or  offensive  in  a  relative  sense  only,  for  many 
animals  pass  their  existence  in  the  midst  of  odors  which  to  us  are  highly 
disagreeable.  A  great  difference  in  this  respect  is.  indeed,  observed 
amongst  men:  many  odors,  generally  thought  agreeable,  are  to  some  per- 
sons intolerable;  and  different  persons  describe  differently  the  sensations 
that  they  severally  derive  from  the  same  odorous  substances.  There  seems 
also  to  be  in  some  persons  an  insensibility  to  certain  odoi*s,  comparable 
with  that  of  the  eye  to  certain  colors;  and  among  different  persons,  as 
great  a  difference  in  the  acuteness  of  the  sense  of  smell  as  among  others 
in  the  acuteness  of  sight.  We  have  no  exact  proof  that  a  relation  of  liar- 
mony  and  disharmony  exists  between  odors  as  between  colors  and  sounds; 
though  it  is  probable  that  such  is  the  case,  since  it  certainly  is  so  with 
regard  to  the  sense  of  taste;  and  since  such  a  relation  would  account  in 
some  measure  for  the  different  degrees  of  perceptive  power  in  different 


E    E  01/ 

Fig.  356.— Epithe- 
lial and  olfaetory 
cells  of  man.  The 
letters  are  placed 
on  the  free  surface. 
E.  E,  epitheUal 
cells;  01/.,  olfac- 
tory cells,  (yias. 
Schiiltze.) 


THE  SENSES. 


179 


persons;  for  as  some  have  no  ear  for  music  (as  it  is  said),  so  others  have 
no  clear  appreciation  of  the  relation  of  odors,  and  therefore  little  pleasure 
in  them. 

Subjective  Sensations  of  Smell. — The  sensations  of  the  olfactory 
nerves,  independent  of  the  external  application  of  odorous  substances, 
have  hitherto  been  little  studied.  The  friction  of  the  electric  machine 
produces  a  smell  liJie  that  of  phosphorus.  Eitter,  too,  has  observed,  that 
when  galvanism  is  applied  to  the  organ  of  smell,  besides  the  impulse  to 
sneeze,  and  the  tickling  sensation  excited  in  the  filaments  of  the  fifth 
nerve,  a  smell  like  that  of  ammonia  was  excited  by  the  negative  pole,  and 
an  acid  odor  by  the  positive  pole;  whichever  of  these  sensations  were 
produced,  it  remained  constant  as  long  as  the  circle  was  closed,  and 
changed  to  the  other  at  the  moment  of  the  circle  being  opened.  Subjec- 
tive sensations  occur  frequently  in  connection  with  the  sense  of  smell. 
Frequently  a  person  smells  something  which  is  not  present,  and  which 
other  persons  cannot  smell;  this  is  very  frequent  with  nervous  people,  but 
it  occasionally  happens  to  every  one.  In  a  man  who  was  constantly  con- 
scious of  a  bad  odor,  the  arachnoid  was  found  after  death  to  be  beset 
with  deposits  of  bone;  and  in  the  middle  of  the  cerebral  hemispheres  were 
scrofulous  cysts  in  a  state  of  suppuration.  Dubois  was  acquainted  with  a 
man  who,  ever  after  a  fall  from  his  horse,  which  occurred  several  years 
before  his  death,  believed  that  he  smelt  a  bad  odor. 

Heakin^g. 

Anatomy  of  the  Ear.— For  descriptive  purposes,  the  Ear,  or  Organ 
of  Hearing,  is  divided  into  three  parts,  (1)  the  external,  (2)  the  middle^ 
and  (3)  the  interyial  ear.  The  two  first  are  only  accessory  to  the  third  or 
internal  ear,  which  contains  the  essential  parts  of  an  organ  of  hearing. 
The  accompanying  figure  shows  very  well  the  relation  of  these  divisions, 
—one  to  the  other  (Fig.  357). 

(1.)  External  Ear. — The  external  ear  consists  ot  the  pinna  or  aitride, 
and  the  external  auditory  canal  or  meatus. 

The  principal  parts  of  the  pinna  (Fig.  358,  a)  are  two  prominent  rims 
enclosed  one  within  the  other  (helix  and  antihelix),  and  enclosing  a  central 
hollow  named  the  concha;  in  front  of  the  concha,  a  prominence  directed 
backward,  the  tragus,  and  opposite  to  this,  one  directed  forward,  the 
antitragus.  From  the  concha,  the  auditory  canal,  with  a  slight  arch  di- 
rected upward,  passes  inward  and  a  little  forward  to  the  membrana  tym- 
pani,  to  which  it  thus  serves  to  convey  the  vibrating  air.  Its  outer  part 
consists  of  fibro-cartilage  continued  from  the  concha;  its  inner  part  of 
bone.  Both  are  lined  by  skin  continuous  with  that  of  the  pinna,  and 
extending  over  the  outer  part  of  the  membrana  tympani. 

Toward  the  outer  part  of  the  canal  are  fine  hairs  and  sebaceous  glands, 
while  deeper  in  the  canal  are  small  glands,  resembling  the  sweat-glands* 


180 


lIAND-liOOK  OF  PHYSIOLOGY. 


in  structure,  wliicli  secrete  a  peculiar  yellow  substance  called  cerumen^ 
or  ear-wax. 

(2.)  Middle  Ear  or  Ty7npanum. — The  middle  ear,  or  tympanum 
(3,  Fig.  357),  is  separated  by  the  memhrana  tymimni  from  the  external 
auditory  canal.  It  is  a  cavity  in  the  temporal  bone,  opening  through  its 
anterior  and  inner  wall  into  the  Eustachian  tube,  a  cylindriform  flattened 
canal,  dilated  at  both  ends,  composed  partly  of  bone  and  partly  of  carti- 
lage, and  lined  Avith  mucous  membrane,  which  forms  a  communication 
between  the  tympanum  and  the  pharynx.  It  opens  into  the  cavity  of 
the  pharynx  just  behind  the  posterior  aperture  of  the  nostrils.    The  cavity 


Fig.  357.— Diagrammatic  view  from  before  of  the  parts  composing  the  organ  of  hearing  of  the 
left  side.  The  temporal  bone  of  the  left  side,  with  the  accompanying  soft  parts,  has  been  detached 
from  the  head,  and  a  section  has  been  carried  through  it  transverselj',  so  as  to  remove  the  front  of 
the  meatus  externus,  half  the  tjmipanic  membrane,  the  upper  and  anterior  wall  of  the  tympanum 
and  Eustachian  tube.  The  meatus  internus  has  also  been  opened,  and  the  bonj-  labyrinth  exposed 
hy  the  removal  of  the  surrounding  parts  of  the  petrous  bone.  1.  the  pinna  and  lobe;  -2,  2',  meatus 
externus;  2',  membrana  tympani:  3.  cavit.y  of  the  tympanum;  3',  its  opening  backAvard  into  the  mas- 
toid cells;  between  3  and  3',  the  chain  of  small  boiies;  4,  Eustachian  tube;" 5,  meatus  internus,  con- 
taining the  facial  (uppei-most)  and  the  auditoiy  nerves;  6,  placed  on  the  vestibule  of  the  labj'rinth 
above  the  fenestra  ovalis;  a,  apex  of  the  petrous  bone;  6,  internal  carotid  arterj*;  o,  stjdoid  process; 
c7,  facial  nerve  issuing  from  the  stylo-mastoid  foramen;  e,  mastoid  process;  /,  squamous  pai't  of  the 
bone  covered  by  integument,  etc.  (Arnold.) 


of  the  tympanum  communicates  posteriorly  with  air-cavities,  the  mastoid 
cells  in  the  mastoid  process  of  the  temporal  bone;  but  its  only  opening 
to  the  external  air  is  through  the  Eustachian  tube  (4,  Fig.  357).  The 
walls  of  the  tym})anum  are  osseous,  except  where  apertures  in  them  are 
closed  with  membrane,  as  at  the  fenestra  rotunda,  and  fenestra  ovalis, 
and  at  the  outer  part  where  the  bone  is  replaced  by  the  memhrana  tym- 
pani. The  cavity  of  tlie  tympaniun  is  lined  with  mucous  membrane,  the 
epithelium  of  wliich  is  ciliated  and  continuous  with  that  of  the  pharynx. 


THE  SENSES. 


181 


It  contains  a  chain  of  small  bones  {Ossicula  auditits)  which  extends  from 
the  membrana  tympani  to  the  fenestra  ovalis. 

The  membrana  tympani  is  placed  in  a  slanting  direction  at  the  bottom 
of  the  external  auditory  canal,  its  plane  being  at  an  angle  of  about  45° 
with  the  lower  wall  of  the  canal.  It  is  formed  chiefly  of  a  tough  and 
tense  fibrous  membrane,  the  edges  of  which  are  set  in  a  bony  groove;  its 
outer  surface  is  covered  with  a  continuation  of  the  cutaneous  lining  of  tlie 
auditory  canal,  its  inner  surface  with  part  of  the 
ciliated  mucous  membrane  of  the  tympanum. 

The  small  bones  or  ossicles  of  the  ear  are  three; 
named  malleus,  incus,  and  stapes.  The  malleus,  or 
hammer-bone,  is  attached  by  a  long  slightly  curved 
process,  called  its  handle,  to  the  membrana  tympani; 
the  line  of  attachment  being  vertical,  including  the 
whole  length  of  the  handle,  and  extending  from  the 
upper  border  to  the  centre  of  the  membrane.  The 
head  of  the  malleus  is  irregularly  rounded;  its  neck, 
or  the  line  of  boundary  between  it  and  the  handle, 
supports  two  processes;  a  short  conical  one,  which 
receives  the  insertion  of  the  tensor  tympani,  and 
a  slender  one,  processus  glacilis,  which  extends  for- 
ward, and  to  which  the  laxator  tympani  muscle  is 
Fig  358  -Outer  surface  attached.  The  incus,  or  anvil-bouc,  shaped  like  a 
of  the  pinna  of  the  right  bicuspid  molar  tooth,  is  articulatcd  by  its  broader 
of  "he  heiix^^s^^antiheu^^  part,  corresponding  with  the  surface  of  the  crown  of 
4,fossaof  theantiheiix;5;       tooth,  to  the  mallcus.    Of  its  two  faug-like  pro- 

antitragus;  6,  tragus;  7,  '        Tiiii  ti  j?  titt 

concha;  8,  lobule.  ccsscs,  ouc,  directed  backward,  has  a  tree  end  lodged 

in  a  depression  in  the  mastoid  bone;  the  other,  curved 
downward  and  more  pointed,  articulates  by  means  of  a  roundish  tuber- 
cle, formerly  called  os  orbicular e,  with  the  stapes,  a  little  bone  shaped 
exactly  like  a  stirrup,  of  which  the  base  or  bar  fits  into  the  fenestra 
ovalis.  To  the  neck  of  the  stapes,  a  short  process,  corresponding  with 
the  loop  of  the  stirrup,  is  attached  the  stapedius  muscle. 

The  Ossicula. — The  bones  of  the  ear  are  covered  with  mucous 
membrane  reflected  over  them  from  the  wall  of  the  tympanum;  and  are 
movable  both  altogether  and  one  upon  the  other.  The  malleus  moves 
and  vibrates  with  every  movement  and  vibration  of  the  membrana  tympani, 
and  its  movements  are  communicated  through  the  incus  to  the  stapes, 
and  through  it  to  the  membrane  closing  the  fenestra  ovalis.  The  malleus, 
also,  is  movable  in  its  articulation  with  the  incus;  and  the  membrana 
tympani  moving  with  it  is  altered  in  its  degree  of  tension  by  the  laxator 
and  tensor  tympani  muscles.  The  stapes  is  movable  on  the  process  of  the 
incus,  when  the  stapedius  muscle  acting,  draws  it  backward.  The  axis 
round  which  the  malleus  and  incus  rotate  is  the  line  joining  the  processus 
gracilis  of  the  malleus  and  the  posterior  (short)  process  of  the  incus. 

(3.)  Internal  Ear. — The  proper  organ  of  hearing  is  formed  by  the  dis- 
tribution of  the  auditory  nerve  within  the  internal  ear,  or  labyrinth  of 
the  ear,  a  set  of  cavities  within  the  petrous  portion  of  the  temporal  bone. 


182 


HAND-BOOK  OF  PHYSIOLOGY. 


The  bone  which  forms  the  walls  of  these  cavities  is  denser  than  that 
around  it,  and  forms  the  osseous  lahyrintli;  the  membrane  within  the 
cavities  forms  the  membranous  lahyrintli.  The  membranous  labyrinth 
contains  a  fluid  called  endoly^nph;  while  outside  it,  between  it  and  the 
osseous  labyrinth,  is  a  fluid  called  perilymph. 

The  osseous  labyrinth  consists  of  three  principal  parts,  namely,  the 
vestihule,  the  cochlea,  and  the  semicircular  canals. 

The  vestibule  is  the  middle  cavity  of  the  labyrinth  and  the  central 
organ  of  the  whole  auditory  apparatus.  It  presents,  in  its  inner  wall, 
several  openings  for  the  entrance  of  the  divisions  of  the  auditory  nerve; 
in  its  outer  wall,  the  fenestra  ovalis  (2,  Fig.  359),  an  opening  filled  by 
the  base  of  the  stapes,  one  of  the  small  bones  of  the  ear;  in  its  posterior 


Fig.  359.  Fig.  360. 

Fig.  359.— Right  bony  labyrinth,  viewed  from  the  outer  side.  The  specimen  here  represented  is 
prepared  by  separating  piecemeal  the  looser  substance  of  the  petrous  bone  from  the  dense  Myalls 
which  immediately  enclose  the  labyrinth.  1,  the  vestibule;  2,  fenestra  ovahs;  3,  superior  semicircu- 
lar canal;  4,  horizontal  or  external  canal;  5, posterior  canal;  *,  ampullae  of  the  semicircular  canals;  6, 
first  turn  of  the  cochlea;  7,  second  turn;  8,  apex;  9,  fenestra  rotimda.  The  smaller  figui-e  in  outline 
below  shows  the  natural  size.   2J£.  (Sommering.) 

1 

Fig.  360.— View  of  the  interior  of  the  left  labyrinth.  The  bony  wall  of  the  labyrinth  is  removed 
superiorly  and  externally.  1,  fovea  hemielliptica;  2,  fovea  hemispherica;  3,  common  opening  of  the 
superior  and  posterior  semicircular  canals;  4,  opening  of  the  aqueduct  of  the  vestibule;  5,  the  supe- 
rior, 6,  the  posterior,  and  7,  the  external  semicircular  canals;  8,  spiral  tube  of  the  cochlea  (scala 
tympani);  9,  opening  of  the  aqueduct  of  the  cochlea;  10,  placed  on  the  lamina  spiralis  in  the  scala 
vestibuh.  2^.  (Sommering.) 
1 

and  superior  walls,  five  openings  by  which  the  semicircular  canals  com- 
municate with  it:  in  its  anterior  wall,  an  opening  leading  into  the 
cochlea.  The  hinder  part  of  the  inner  wall  of  the  vestibule  also  presents 
an  opening,  the  orifice  of  the  aqimductus  vestibuli,  a  canal  leading  to  the 
posterior  margin  of  the  petrous  bone,  with  uncertain  contents  and  un- 
known purpose. 

The  semicircular  canals  (Figs.  359,  300),  are  three  arched  cylin- 
driform  bony  canals,  set  in  the  substance  of  the  petrous  bone.  They 
all  open  at  both  ends  into  the  vestibule  (two  of  them  first  coalescing). 
The  ends  of  each  are  dilated  just  before  opening  into  the  vestibule; 
and  one  end  of  each  being  more  dilated  than  the  other  is  called  an 
ampulla,  ''l^vo  of  the  canals  foi-in  nearly  vertical  arc^lios;  of  these  the 
superior  is  also  anterior;  tlu^  ])osterior  is  inferior;  tlie  third  canal  is  hori- 
zontal, and  lower  and  shorter  than  tlie  others. 


THE  SENSES. 


183 


The  cochlea  (6,  7,  8,  Figs.  359- and  360),  a  small  organ,  shaped  like 
a  common  snail-shell,  is  seated  in  front  of  the  vestibule,  its  base  rest- 
ing on  the  bottom  of  the  internal  meatus,  where  some  apertures  transmit 
to  it  the  cochlear  filaments  of  the  auditory  nerve.  In  its  axis,_  the  cochlea 
is  traversed  by  a  conical  column,  the  modiolus,  around  which  a  spiral 
canal  winds  with  about  two  turns  and  a  half  from  the  base  to^  the  apex. 
At  the  apex  of  the  cochlea  the  canal  is  closed;  at  the  base  it  presents 
three  openings,  of  which  one,  already  mentioned,  communicates  with  the 
vestibule;  another  called  fenestra  rotunda,  is  separated  by  a  membrane 
from  the  cavity  of  the  tympanum;  the  third  is  the  orifice  of  the  aquce- 
ductus  coclilem,  a  canal  leading  to  the  jugular  fossa  of  the  petrous  bone, 
and  corresponding,  at  least  in  obscurity  of  purpose  and  origin,  to  the 
aquseductus  vestibuli.    The  spiral  canal  is  divided  into  two  passages,  or 


Fig.  361. — View  of  the  osseous  cochlea  divided  through  the  middle.  1,  central  canal  of  the  modio- 
lus; 2,  lamina  spiralis  ossea;  3,  scala  tympani;  4,  scala  vestibuli ;  5,  porous  substance  of  the  modiolus 
near  one  of  the  sections  of  the  canalis  spiralis  modioli.   _5 .  (Arnold.) 

Fig.  362.— Section  through  one  of  the  coils  of  the  cochlea  (diagrammatic).  8  T,  scala  tympani ;  S  F, 
scala  vestibuli;  C  C,  canalis  cochleae  or  canalis  membranaceus;  i?,  membrane  of  Reissner;  I  s  o, 
lamina  spiralis  ossea;  1 1  s,  limbus  laminfe  spiralis;  s  s,  sulcus  spiralis;  n  c,  cochlear  nerve;  grs,  gang- 
Uon  spirale;  membrana  tectoria  (below  the  membrana  tectoria  is  the  lamina  reticularis);  &,  mem- 
brana  basilaris;  Co,  rods  of  Corti;  Isp,  ligamentum  spirale.   (From  Quain's  Anatomy.) 


scalae,  by  a  partition  of  bone  and  membrane,  the  lamina  spiralis.  The 
osseous  part  or  zone  of  this  lamina  is  connected  with  the  modiolus;  the 
membranous  part,  with  a  muscular  zone,  according  to  Todd  and  Bowman, 
forming  its  outer  margin,  is  attached  to  the  outer  wall  of  the  canal. 
Commencing  at  the  base  of  the  cochlea,  between  its  vestibular  and  tym- 
panic openings,  they  form  a  partition  between  these  apertures;  the  two  scalae 
are,  therefore,  in  correspondence  with  this  arrangement,  named  scala 
vestibuli  and  scala  tympani  (Fi^.  361).  At  the  apex  of  the  cochlea,  the 
lamina  spiralis  ends  in  a  small  hamulus,  the  inner  and  concave  part  of 
which,  being  detached  from  the  summit  of  the  modiolus,  leaves  a  small 
aperture  named  helicotrema,  by  which  the  two  scalse,  separated  in  all 
the  rest  of  their  length,  communicate. 

Besides  the  ''scala  vestibuli^^  and  "scala  tympani,"  there  is  a  third 
space  between  them,  called  scala  media  or  canalis  memhranaceus  (CO,  Fig 
362).  In  section  it  is  triangular,  its  external  wall  being  formed  by  the 
wall  of  the  cochlea,  its  upper  wall  (separating  it  from  the  scala  vestibuli) 
by  the  membrane  of  Eeissner,  and  its  lower  wall  (separating  it  from  the 
scala  tympani)  by  the  basilar  membrane,  these  two  meeting  at  the  outer 


Fig.  361. 


Fig.  362. 


184 


HAND-BOOK  OF  PHYSIOLOGY. 


edge  of  the  bony  lamina  spiralis.  Following  the  turns  of  the  cochlea  to  its 
apex,  the  scala  media  there  terminates  blindly;  while  toward  the  base  of 
the  cochlea  it  is  also  closed  with  the  exception  of  a  very  narrow  passage 
(canalis  reuniens)  uniting  it  with  the  sacculus.  The  scala  media  (like  the 
rest  of  the  membranous  labyrinth)  contains  "endolymph." 

Organ  of  Corti. — Upon  the  basilar  membrane  are  arranged  cells  of 
various  shapes. 

About  midway  between  the  outer  edge  of  the  lamina  spiralis  and  the 
outer  wall  of  the  cochlea  are  situated  the  rods  of  Corti.  Viewed  sideways, 
the  rods  of  Corti  are  seen  to  consist  of  an  external  and  internal  pillar, 
each  rising  from  an  expanded  foot  or  base  on  the  basilar  membrane. 
They  slant  inward  toward  each  other,  and  each  ends  in  a  swelling  termed 
the  head;  the  head  of  the  inner  pillar  overlying  that  of  the  outer  (Fig. 


Fig.  363.— Vertical  section  of  the  organ  of  Corti  from  the  dog.  1  to  2,  homogeneous  layer  of  the 
so-called  membrana  basilaris;  tt,  vestibular  layer;  v,  tympanal  layer,  with  nuclei  and  protoplasm: 
a,  prolongation  of  tympanal  periosteum  of  lamina  spiralis  ossea;  c,  thickened  commencement  of 
the  memlDrana  basilaris  near  the  point  of  perforation  of  the  nerves  li;  d,  blood-vessel,  (vas  spirale); 
e,  blood-vessel;  /,  nerves;  g,  the  epithelium  of  the  sulcus  spiralis  internus;  i,  internal  or  tufted  cell, 
with  basil  process  fc,  surrounded  with  nuclei  and  protoplasm  (of  the  granular  layer),  into  which  the 
nerve-fibres  radiate;  I,  hairs  of  the  internal  hair-cell;  ii,  base  or  foot  of  inner  pillar  of  organ  of  Corti; 
m,  head  of  the  same  uniting  with  the  corresponding  part  of  an  external  pillar,  whose  under  half  is 
missing,  while  the  next  pillar  beyond,  o,  presents  both  middle  portion  and  base;  r,  s,  d,  three  external 
hair-cells;  i,  bases  of  two  neighboring  hair  or  tufted  cells;  x,  so-called  supporting  cell  of  Hensen;  w, 
nerve  fibre  terminating  in  the  first  of  the  external  hair-cells;  1 1  to  I,  lamina  reticularis,  x  SOO. 
(Waldeyer.) 

363).  Each  pair  of  pillars  forms,  as  it  were,  a  pointed  roof  arching  over 
a  space,  and  by  a  succession  of  them,  a  little  tunnel  is  formed. 

It  has  been  estimated  that  there  are  about  3000  of  these  pairs  of  pillars, 
in  proceeding  from  the  base  of  the  cochlea  toward  its  apex.  They  are 
found  progressively  to  increase  in  length,  and  become  more  oblique;  in 
other  words,  the  tunnel  becomes  wider,  but  diminishes  in  height  as  we 
ap])roach  the  apex  of  the  cochlea.  Leaning,  as  it  Avere,  against  these 
external  and  internal  pillars  are  certain  other  cells,  of  which  the  external 
ones  terminate  in  small  hair-like  processes.  Most  of  the  above  details 
are  shown  in  the  accompanying  figure  (Fig.  363).  This  complicated 
structure  rests,  as  we  have  seen,  upon  the  basilar  membrane;  it  is  roofed 
in  by  a  remarka])]e  fenestrated  membrane  (lamina  reticularis  of  KoUiker), 
into  the  fenestrie  of  whicli  tlie  tops  of  the  various  rods  and  cells  are  re- 
ceived.   When  viewed  from  above,  tlie  organ  of  Corti  shows  a  remarkable 


THE  SENSES. 


185 


resemblance  to  the  key-board  of  a  piano.  In  c\oso  relation  with  the  rods 
of  Corti  and  the  cells  inside  and  outside  them,  and  probably  projecting 
by  free  ends  into  the  little  "tunnel"  containing  fluid  (roofed  in  by  them), 
are  filaments  of  the  auditory  nerve. 

Membranous  Labyrinth.— This  corresponds  generally  with  the 
form  of  the  osseous  labyrinth,  so  far  as  regards  the  vestibule  and  semi- 
circular canals,  but  is  separated  from  the  walls  of  these  parts  by  fluid, 
except  where  the  nerves  enter  into  connection  within  it.  As  already  men- 
tioned, the  membranous  labyrinth  contains  a  fluid  called  endolympli;  and 
between  its  outer  surface  and  the  inner  surface  of  the  walls  of  the  vesti- 
bule and  semicircular  canals  is  another  collection  of  similar  fluid,  called 
yerilympli;  so  that  all  the  sonorous  vibrations  impressing  the  auditory 
nerves  on  these  parts  of  the  internal  ear,  are  conducted  through  fluid  to 
a  membrane  suspended  in  and  containing  fluid.  In  the  cochlea,  the 
membranous  labyrinth  completes  the  septum  between  the  two  scalm  and 
encloses  a  spiral  canal,  previously  mentioned,  called  canalis  membranaceus 
or  canalis  cochlem  (Fig.  362).  The  fluid  in  the  scalcB  of  the  cochlea  is  con- 
tinuous with  the  perilymph  in  the  vestibule  and  semicircular  canals,  and 
there  is  no  fluid  external  to  its  lining  membrane.  The  vestibular  portion 
of  the  membranous  labyrinth  comprises  two,  probably  communicating 
cavities,  of  which  the  larger  and  upper  is  named  the  utriculus;  the  lower, 
the  sacculus.  They  are  lodged  in  depressions  in  the  bony  labyrinth 
termed  respectively  "fovea  hemielliptica^^  and  "fovea  hemispherica.^' 
Into  the  former  open  the  orifices  of  the  membranous  semicircular  canals; 
into  the  latter  the  canalis  cochlem.  The  membranous  labyrinth  of  all 
these  parts  is  laminated,  transparent,  very  vascular,  and  covered  on  the 
inner  surface  with  nucleated  cells,  of  which  those  that  line  the  ampullae 
are  prolonged  into  stiff  hair-like  processes;  the  same,  appearance,  but  to  a 
much  less  degree,  being  visible  in  the  iitricule  and  saccule.  In  the  cavities 
of  the  utriculus  and  sacculus  are  small  masses  of  calcareous  particles, 
otoconia  or  otoliths;  and  the  same,  although  in  more  minute  quantities,  are 
to  be  found  in  the  interior  of  some  other  parts  of  the  membranous 
labyrinth. 

Auditory  Nerve. — For  the  appropriate  exposure  of  the  filaments  of 
the  auditory  nerve  to  sonorous  vibrations  all  the  organs  now  described  are 
provided.  It  is  characterized  as  a  nerve  of  special  sense  by  its  softness 
(whence  it  derived  its  name  of  portio  mollis  of  the  seventh  pair)  and  by 
the  fineness  of  its  component  fibres.  It  enters  the  labyrinth  of  the  ear 
in  two  divisions;  one  for  the  vestibule  and  semicircular  canals,  and  the 
other  for  the  cochlea. 

The  branches  for  the  vestibule  spread  out  and  radiate  on  the  inner 
surface  of  the  membranous  labyrinth:  their  exact  termination  is  unknown. 
Those  for  the  semicircular  canals  pass  into  the  ampullae,  and  form,  within 
each  of  them,  a  forked  projection  which  corresponds  with  a  septum  in  the 


186 


HAND-BOOK  OF  PHYSIOLOGY. 


interior  of  the  ampulla.  The  branches  for  the  cochlea  enter  it  through 
orifices  at  the  base  of  the  modiolus,  which  they  ascend,  and  thence  suc- 
cessively pass  into  canals  in  the  osseous  part  of  the  lamina  spiralis.  In 
the  canals  of  this  osseous  part  or  zone,  the  nerves  are  arranged  in  a  plexus, 
containing  ganglion  cells.  Their  ultimate  termination  is  not  known  with 
certainty;  but  some  of  them,  without  doubt,  end  in  the  organ  of  Corti, 
probably  in  cells. 

Physiology  of  Heakii^g. 

All  the  acoustic  contrivances  of  the  organ  of  hearing  are  means  for 
conducting  the  sound,  ju§t  as  the  optical  apparatus  of  the  eye  are  media 
for  conducting  the  light.  Since  all  matter  is  capable  of  propagating  sono- 
rous vibrations,  the  simplest  conditions  must  be  sufficient  for  mere  hear- 
ing; for  all  substances  surrounding  the  auditory  nerve  Avould  communi- 
cate sound  to  it.  The  whole  development  of  the  organ  of  hearing,  there- 
fore, can  have  for  its  object  merely  the  rendering  more  i)erfect  the  propa- 
gation of  the  sonorous  vibrations,  and  their  miLUiylication  by  resonance; 
and,  in  fact,  all  the  acoustic  apparatus  of  the  organ  may  be  shown  to  have 
reference  to  these  two  principles. 

Functions  of  the  External  Ear. — The  external  auditory  passage 
influences  the  propagation  of  sound  to  the  tympanum  in  three  ways : — 1, 
by  causing  the  sonorous  undulations,  entering  directly  from  the  atmos- 
phere, to  be  transmitted  by  the  air  in  the  passage  immediately  to  the 
membrana  tympani,  and  thus  preventing  them  from  being  dispersed;  2, 
by  the  walls  of  the  passage  conducting  the  sonorous  undulations  imparted 
to  the  external  ear  itself,  by  the  shortest  path  to  the  attachment  of  the 
membrana  tympani,  and  so  to  this  membrane;  3,  by  the  resonance  of  the 
column  of  air  contained  witliin  the  passage;  4,  the  external  ear,  especially 
when  the  tragus  is  provided  with  hairs,  is  also,  doubtless,  of  service  in 
protecting  the  meatus  and  membrana  tympani  against  dust,  insects,  and 
the  like. 

1.  As  a  conductor  of  undulations  of  air,  the  external  auditory  passage 
receives  the  direct  undulations  of  the  atmosphere,  of  which  those  that 
enter  in  the  direction  of  its  axis  produce  the  strongest  impressions.  The 
undulations  which  enter  the  passage  obliquely  are  reflected  by  its  parietes, 
aiid  thus  by  reflexion  reach  the  membrana  tympani. 

2.  The  walls  of  the  meatus  are  also  solid  conductors  of  sound;  for 
those  vil)nitions  which  are  communicated  to  the  cartilage  of  the  external 
car,  and  not  reflected  from  it,  are  propagated  by  tlie  shortest  path  through 
the  parietes  of  the  passage  to  the  membrana  tympani.  Hence,  both  ears 
being  close  stopped,  the  sound  of  a  pi])e  is  heard  more  distinctly  when  its 
lower  extremity,  covered  with  a  membrane,  is  applied  to  the  cartilage  of 
the  external  ear  itself,  than  when  it  is  placed  in  contact  with  the  surface 
of  the  head. 


THE  SENSES. 


187 


3.  The  external  auditory  passage  is  important,  inasmuch  as  the  air 
which  it  contains,  like  all  insulated  masses  of  air,  increases  the  intensity 
of  sounds  by  resonance. 

Kegarding  the  cartilage  of  the  external  ear,  therefore,  as  a  conductor 
of  sonorous  vibrations,  all  its  inequalities,  elevations,  and  depressions, 
which  are  useless  with  regard  to  reflexion,  become  of  evident  importance; 
for  those  elevations  and  depressions  upon  which  the  undulations  fall  per- 
pendicularly, will  be  affected  by  them  in  the  most  intense  degree;  and, 
in  consequence  of  the  various  forms  and  positions  of  these  inequalities, 
sonorous  undulations,  in  whatever  direction  they  may  come,  must  fall 
perpendicularly  upon  the  tangent  of  some  one  of  them.  This  affords  an 
explanation  of  the  extraordinary  form  given  to  this  part. 

Functions  of  the  Middle  Ear. — In  animals  living  in  the  atmos- 
phere, the  sonorous  vibrations  are  conveyed  to  the  auditory  nerve  by  three 
different  media  in  succession;  namely,  the  air,  the  solid  parts  of  the  body 
of  the  animal  and  of  the  auditory  apparatus,  and  the  fluid  of  the  laby- 
rinth. Sonorous  vibrations  are  imparted  too  imperfectly  from  air  to  solid 
bodies,  for  the  propagation  of  sound  to  the  internal  ear  to  be  adequately 
effected  by  that  means  alone;  yet  already  an  instance  of  its  being  thus 
propagated  has  been  mentioned.  In  passing  from  air  directly  into  water, 
sonorous  vibrations  suffer  also  a  considerable  diminution  of  their  strength; 
but  if  a  tense  membrane  exists  between  the  air  and  the  water,  the  sono- 
rous vibrations  are  communicated  from  the  former  to  the  latter  medium 
with  very  great  intensity.  This  fact,  of  which  Miiller  gives  experimental 
proof,  furnishes  at  once  an  explanation  of  the  use  of  the  fenestra  rotunda, 
and  of  the  membrane  closing  it.  They  are  the  means  of  communicating, 
in  full  intensity,  the  vibrations  of  the  air  in  the  tympanum  to  the  fluid 
of  the  labyrinth.  This  peculiar  property  of  membranes  is  the  result,  not 
of  their  tenuity  alone,  but  of  the  elasticity  and  capability  of  displacement 
of  their  particles;  and  it  is  not  impaired  when,  like  the  membrane  of  the 
fenestra  rotunda,  they  are  not  impregnated  with  moisture. 

Sonorous  vibrations  are  also  communicated  without  any  perceptible 
loss  of  intensity  from  the  air  to  the  water,  when  to  the  membrane  form- 
ing the  medium  of  communication,  there  is  attached  a  short,  solid  body, 
which  occupies  the  greater  part  of  its  surface,  and  is  alone  in  contact  with 
the  water.  This  fact  elucidates  the  action  of  the  fenestra  ovalis,  and  of 
the  plate  of  the  stapes  which  occupies  it,  and,  with  the  preceding  fact, 
shows  that  both  fenestrse — that  closed  by  membrane  only,  and  that  with 
which  the  movable  stapes  is  connected — transmit  very  freely  the  sonorous 
vibrations  fromx  the  air  to  the  fluid  of  the  labyrinth. 

A  small,  solid  body,  fixed  in  an  opening  by  means  of  a  border  of  mem- 
brane, so  as  to  be  movable,  communicates  sonorous  vibrations  from  air  on 
the  one  side,  to  water,  or  the  fluid  of  the  labyrinth,  on  the  other  side, 
much  better  than  solid  media  not  so  constructed.    But  the  propagation 


188 


HAND-BOOK  OF  PHYSIOLOGY. 


of  sound  to  the  fluid  is  rendered  much  more  perfect  if  the  solid  conductor 
thus  occu23ying  the  opening,  or  fenestra  ovalis,  is  by  its  other  end  fixed  to 
the  middle  of  a  tense  membrane,  which  has  atmospheric  air  on  both  sides. 
A  tense  membrane  is  a  much  better  conductor  of  the  vibrations  of  air 
than  any  other  solid  body  bounded  by  definite  surfaces:  and  the  vibra- 
tions are  also  communicated  very  readily  by  tense  membranes  to  solid 
bodies  in  contact  with  them.  Thus,  then,  the  memhrana  tympmii  serves 
for  the  transmission  of  sound  from  the  air  to  the  chain  of  auditory  bones. 
Stretched  tightly  in  its  osseous  ring,  it  vibrates  with  the  air  in  the  audi- 
tory passage,  as  any  thin  tense  membrane  will^  when  the  air  near  it  is 
thrown  into  vibrations  by  the  sounding  of  a  tuning-fork  or  a  musical 
string.  And,  from  such  a  tense  vibrating  membrane,  the  vibrations  are 
communicated  with  great  intensity  to  solid  bodies  which  touch  it  at  any 
point.  If,  for  example,  one  end  of  a  flat  piece  of  wood  be  applied  to  the 
membrane  of  a  drum,  while  the  other  end  is  held  in  the  hand,  vibrations 
are  felt  distinctly  when  the  vibrating  tuning-fork  is  held  over  the  mem- 
brane without  touching  it;  but  the  wood  alone,  isolated  from  the  mem- 
brane, will  only  very  feebly  propagate  the  vibrations  of  the  air  to  the 
hand. 

In  comparing  the  membrana  tympani  to  the  membrane  of  a  drum,  it 
is  necessary  to  point  out  certain  important  differences. 

When  a  drum  is  struck,  a  certain  definite  tone  is  elicited  (fundamental 
tone) ;  similarly  a  drum  is  thrown  into  vibration  when  certain  tones  are 
sounded  in  its  neighborhood,  while  it  is  quite  unaffected  by  others.  In 
other  words,  it  can  only  take  up  and  vibrate  in  response  to  those  tones 
whose  vibrations  nearly  correspond  in  number  with  those  of  its  own  fun- 
damental tone.  The  tympanic  membrane  can  take  up  an  immense  range 
of  tones  produced  by  vibrations  ranging  from  30  to  4000  or  5000  per 
second.  This  would  be  clearly  impossible  if  it  were  an  evenly  stretched 
membrane. 

The  fact  is,  that  the  tympanic  membrane  is  by  no  means  evenly 
stretched,  and  this  is  due  partly  to  its  slightly  funnel-like  form,  and  partly 
to  its  being  connected  with  the  chain  of  auditory  ossicles.  Further,  if 
the  membrane  were  quite  free  in  its  centre,  it  would  go  on  vibrating  as  a 
drum  does  some  time  after  it  is  struck,  and  each  sound  Avould  be  pro- 
longed, leading  to  considerable  confusion.  This  evil  is  obviated  by  the 
ear-bones,  which  check  the  continuance  of  the  vibrations  like  the  ''dam- 
pers" in  a  pianoforte. 

The  ossicula  of  the  ear  are  the  better  conductors  of  the  sonorous 
vibrations  communicated  to  them,  on  account  of  being  isolated  by  an 
atmosphere  of  air,  and  not  continuous  with  the  bones  of  the  cranium;  for 
every  solid  body  tlius  isolated  by  a  different  medium,  propagates  vibra- 
tions with  more  intensity  tlirougli  its  own  substance  than  it  communicates 
tliem  to  tlic  surrounding  medium,  which  tlius  prevents  a  dispersion  of 
tlie  sound;  just  as  tlic  vibrations  of  the  air  in  the  tubes  used  for  conduct- 
ing the  voice  from  one  apartment  to  another  are  prevented  from  being 


THE  SENSES. 


189 


dispersed  by  the  solid  walls  of  the  tube.  The  vibrations  of  the  mem- 
brana  tympani  are  transmitted,  therefore,  by  the  chain  of  ossicula  to  the 
fenestra  ovalis  and  fluid  of  the  labyrinth,  their  dispersion  in  the  tym- 
panum being  prevented  by  the  difficulty  of  the  transition  of  vibrations 
from  solid  to  gaseous  bodies. 

The  necessity  of  the  presence  of  air  on  the  inner  side  of  the  membrana 
tympani,  in  order  to  enable  it  and  the  ossicula  auditus  to  fulfil  the  objects 
just  described,  is  obvious.  "Without  this  provision,  neither  would  the 
vibrations  of  the  membrane  be  free,  nor  the  chain  of  bones  isolated,  so  as 
to  propagate  the  sonorous  undulations  with  concentration  of  their  inten- 
sity. But  while  the  oscillations  of  the  membrana  tympani  are  readily 
communicated  to  the  air  in  the  cavity  of  the  tympanum,  those  of  the  solid 
ossicula  will  not  be  conducted  away  by  the  air,  but  will  be  propagated 
to  the  labyrinth  without  being  dispersed  in  the  tympanum. 

The  propagation  of  sound  through  the  ossicula  of  the  tympanum  to 
the  labyrinth,  must  be  effected  either  by  oscillations  of  the  bones,  or  by  a 
kind  of  molecular  vibration  of  their  particles,  or,  most  probably,  by  both 
these  kinds  of  motion. 

Movements  of  tJie  ossicula. — E.  Weber  has  shown  that  the  existence 
of  the  membrane  over  the  fenestra  rotunda  will  permit  approximation  and 
removal  of  the  stapes  to  and  from  the  labyrinth.  When  by  the  stapes 
the  membrane  of  the  fenestra  ovalis  is  pressed  toward  the 
labyrinth,  the  membrane  of  the  fenestra  rotunda  may,  by 
the  pressure  communicated  through  the  fluid  of  the  laby- 
rinth, be  pressed  toward  the  cavity  of  the  tympanum. 

The  long  process  of  the  malleus  receives  the  undula- 
tions of  the  membrana  tympani  (Fig.  364,  a,  a)  and  of 
the  air  in  a  direction  indicated  by  the  arrows,  nearly  per- 
pendicular to  itself.  From  the  long  process  of  the 
malleus  they  are  propagated  to  its  head  {h) :  thence  into 
the  incus  (c),  the  long  process  of  which  is  parallel  with 
the  long  process  of  the  malleus.  From  the  long  process 
of  the  incus  the  undulations  are  communicated  to  the 
stapes  (6^),  which  is  united  to  the  incus  at  right  angles. 
The  several  changes  in  the  direction  of  the  chain  of 
bones  have,  however,  no  influence  on  that  of  the  undu- 
lations, which  remain  the  same  as  it  was  in  the  meatus 
externus  and  long  process  of  the  malleus,  so  that  the  undulations  are 
communicated  by  the  stapes  to  the  fenestra  ovalis  in  •  a  perpendicular 
direction. 

Increasing  tension  of  the  membrana  tympani  diminishes  the  facility 
of  transmission  of  sonorous  undulations  from  the  air  to  it. 

Savart  observed  that  the  dry  membrana  tympani,  on  the  approach  of 
a  body  emitting  a  loud  sound,  rejected  particles  of  sand  strewn  upon  it 
more  strongly  when  lax  than  when  very  tense;  and  inferred,  therefore, 
that  hearing  is  rendered  less  acute  by  increasing  the  tension  of  the  mem- 


FiG.  364. 


190  HAND-BOOK  OF  PHYSIOLOGY. 

brana  tympani.  Miiller  has  confirmed  this  by  experiments  with  small 
membranes  arranged  so  as  to  imitate  the  membrana  tympani;  and  it  may 
be  confirmed  also  by  observations  on  one^s  self. 

The  pharyngeal  orifice  of  the  Eustachian  tube  is  usually  shut;  daring 
.  swallowing,  however,  it  is  opened;  this  may  be  shown  as  follows: — If  the 
'nose  and  mouth  be. closed  and  the  cheeks  blown  out^  a  sense  of  pressure 
.  is  produced  in  both  ears  the  moment  we  swallow;  this  is  due,  doubtless, 
to  the  bulging  out  of  the  tympanic  membrane  by  the  compressed  air 
which,  at  that  moment,  enters  the  Eustachian  tube. 

"Similarly  the  tympanic  membrane  may  be  pressed  in  by  rarefying  the 
V     air  in  the.  tymxpanum.    This  can  be  readily  accomplished  by  closing  the 
^l^^jjplith  and  nose,  and  making  an  inspiratory  effort  and  at  the  same  time 
swallowing  (Valsalva).    In  both  cases  the  sense  of  hearing  is  temporarily 
dulled;  proving  that  equality  of  pressure  on  both  sides  of  the  tympanic 
membrane  is  necessary  for  its  full  efficiency. 

Functions  of  Eustachian  Tube. — The  principal  office  of  the 
Eustachian  tube,  in  Miiller's  opinion,  has  relation  to  the  prevention  of 
these  effects  of  increased  tension  of  the  membrana  tympani.  Its  exist- 
ence and  openness  will  provide  for  the  maintenance  of  the  equilibrium 
between  the  air  within  the  tympanum  and  the  external  air,  so  as  to  pre- 
vent the  inordinate  tension  of  the  membrana  tympani  which  would  be 
produced  by  too  great  or  too  little  pressure  on  either  side.  While  dis- 
charging this  office,  however,  it  will  serve  to  render  sounds  clearer,  as 
(Henle  suggests)  the  apertures  in  violins  do;  to  supply  the  tympanum 
,  with  air;  and  to  be  an  outlet  for  mucus.  If  tlie  Eustachian  tube  were 
permanently  open,  the  sound  of  one's  own  voice  would  probably  be  greatly 
intensified,  a  condition  which  would  of  course  interfere  with  the  percep- 
tion of  other  sounds.  At  any  rate,  it  is  certain  that  sonorous  vibrations 
can  be  propagated  up  the  Eustachian  tube  to  the  tympanum  by  means  of 
a  tube  inserted  into  the  pharyngeal  orifice  of  the  Eustachian  tube. 

Action  of  Tensor  Tympani. — The  influence  of  the  tensor  tympani 
muscle  in  modifying  hearing  may  also  be  probably  explained  in  connec- 
tion with  the  regulation  of  the  tension  of  the  membrana  tympani.  If, 
through  reflex  nervous  action,  it  can  be  excited  to  contraction  by  a  very 
loud  sound,  just  as  the  iris  and  orbicularis  palpebrarum  muscle  are  by 
a  very  intense  light,  then  it  is  manifest  that  a  very  intense  sound  would, 
through  the  action  of  this  muscle,  induce  a  deafening  or  muffling  of  tlie 
ears.  In  favor  of  this  supposition  we  have  tlie  fact  that  a  loud  sound 
excites,  by  reflection,  nervous  action,  winking  of  the  eyelids,  and,  in  per- 
sons of  irritable  nervous  system,  a  sudden  contraction  of  many  muscles. 

"The  ossicula  of  aquatic  mammalia  arc  very  bulky  and  relatively  large, 
especially  in  the  true  seals  and  the  sirenia  (Manatee  and  Dugoug).  In 
the  cetacoa  the  sta])e8  is  generally  ankylosed  to  the  fenestra  ovalis.  the 
malleus  is  alwayx  ankylosed  to  the  tym])auic  bone,  yet  the  nunubrana  tym- 
])ani  is  well  formed,  and  there  is  a  manubrium,  often  ill-developed,  but 
always  attached  to  the  membrane  by  a  long  process.   In  the  Otaria?  or  Sea- 


THE  SENSES. 


191 


lions,  where  the  ossicula  are  far  smaller  relatively,  and  less  ,§dJ id  than  in 
whales,  manatees,  and  the  earless  true  seals,  there  are  jjj^^?Sorrf^S>jnov- 
able  external  ears.  The  ossicula  seem  to  be  vestigiaL^elics  utu^tee^  ipr 
the  auditory  function.  In  land  animals  they  vary  irJ/shape  accorafjj^^  to 
the  type  of  the  animal  rather  than  in  relation  to  its  afuteness  of  hearmg. 
I  have  never  found  a  muscular  laxator  tympani  in  mij  anirrtal,  but  tli$. 
tensor  exists  as  a  ligament  in  whales  where  the  malle J|  is  fixed. "  ,  ( Alban 
Doran.)  >^  >  , 

Action  of  the  Stapedius. — The  influence  of  the  stapeJla^u«  muscle  in 
hearing  is  unknown.  It  acts  upon  the  stapes  in  such  a  malhner  as  to 
make  it  rest  obliquely  in  the  fenestra  ovalis,  depressing  that  side  of-it  im 
which  it  acts,  and  elevating  the  other  side  to  the  same  extent.  It  pre- 
vents too  great  a  movement  of  the  bone. 

Functions  of  the  Fluid  of  the  'LsLbyrinth— The  fluid  of  the  laby- 
rinth is  the  most  general  and  constant  of  the  acoustic  provisions  of  the 
labyrinth.  In  all  forms  of  organs  of  hearing,  the  sonorous  vibrations  affect 
the  auditory  nerve  through  the  medium  of  liquid — the  most  convenient 
medium,  on  many  accounts,  for  such  a  purpose. 

The  crystalline  pulverulent  masses  (otoliths)  in  the  labryinth  would 
reinforce  the  sonorous  vibrations  by  their  resonance,  even  if  they  did  not 
actually  touch  the  membranes  upon  which  the  nerves  are  expanded;  but, 
inasmuch  as  these  bodies  lie  in  contact  with  the  membranous  parts  of  the 
labyrinth,  and  the  vestibular  nerve-fibres  are  imbedded  in  them,  they 
communicate  to  these  membranes  and  the  nerves,  vibratory  impulses  of 
greater  intensity  than  the  fluid  of  the  labyrinth  can  impart.  This  appears 
to  be  their  office.  Sonorous  undulations  in  water  are  not  perceived  by 
the  hand  itself  immersed  in  the  water,  but  are  felt  distinctly  through  the 
medium  of  a  rod  held  in  the  hand.  The  fine  hair-like  prolongations  from 
the  epithelial  cells  of  the  ampullae  have,  probably,  the  same  function. 

Functions  of  the  Semicircular  Canals. — Besides  the  function  of 
collecting  in  their  fluid  contents  sonorous  undulations  from  the  bones  of 
the  cranium,  the  semicircular  canals  appear  to  have  another  function  less 
directly  connected  with  the  sense  of  hearing.  Experiments  show  that 
when  the  horizontal  canal  is  divided  in  a  pigeon  a  constant  movement  of 
the  head  from  side  to  side  occurs,  and  similarly,  when  one  of  the  vertical 
canals  is  operated  upon,  up  and  down  movements  of  the  head  are  ob- 
served. These  movements  are  associated,  also,  with  loss  of  co-ordination, 
as  after  the  operation  the  bird  is  unable  to  fly  in  an  orderly  manner,  but 
flutters  and  falls  when  thrown  into  the  air,  and,  moreover,  is  able  to  feed 
with  difficulty.  Hearing  remains  unimpaired.  It  has  been  suggested, 
therefore,  that  as  loss  of  co-ordination  results  from  section  of  these  canals, 
and  as  co-ordinate  muscular  movements  appear  to  depend  to  a  consider- 
able extent  for  their  due  performance  upon  a  correct  notion  of  our  equili- 
brium, that  the  semicircular  canals  are  connected  in  some  way  with  this 


HAND-BOOK  OF  PHYSIOLOGY. 


sense,  possibly  by  the  constant  alterations  of  the  pressure  of  the  fluid 
within  them;  the  change  in  the  pressure  of  the  fluid  in  each  canal 
which  takes  place  on  any  movement  of  the  head,  producing  sensations 
which  aid  in  forming  an  exact  judgment  of  the  alteration  of  position 
which  has  occurred^ 

Functions  of  the  Cochlea. — The  cochlea  seems  to  be  constructed 
for  the  spreading  out  of  the  nerve-fibres  over  a  wide  extent  of  surface, 
upon  a  solid  lamina  which  communicates  with  the  solid  walls  of  the 
labyrinth  and  cranium,  at  the  same  time  that  it  is  in  contact  with  the 
.fluid  of  the  labyrinth,  and  which,  besides  exposing  the  nerve-fibres  to  the 
influence  of  sonorous  undulations,  by  two  media,  is  itself  insulated  by 
fluid  on  either  side. 

The  connection  of  the  lamina  spiralis  with  the  solid  walls  of  the  laby- 
rinth, adapts  the  cochlea  for  the  perception  of  the  sonorous  undulations 
propagated  by  the  solid  parts  of  the  head  and  the  walls  of  the  labyrinth. 
The  membranous  labyrinth  of  the  vestibule  and  semicircular  canals  is 
suspended  free  in  the  perilymph,  and  is  destined  more  particularly  for  the 
perception  of  sounds  through  the  medium  of  that  fluid,  whether  the  sono- 
rous undulations  be  imparted  to  the  fluid  through  the  fenestrse,  or  by 
the  intervention  of  the  cranial  bones,  as  when  sounding  bodies  are  brought 
into  communication  with  the  head  or  teeth.  The  spiral  lamina  on  which 
the  nervous  fibres  are  expanded  in  the  cochlea,  is,  on  the  contrary,  con- 
tinuous with  the  solid  walls  of  the  labyrinth,  and  receives  directly  from 
them  the  impulses  which  they  transmit.  This  is  an  important  advantage; 
for  the  impulses  imparted  by  solid  bodies  have,  cceteris  pariMos,  a  greater 
absolute  intensity  than  those  communicated  by  water.  And,  even  when 
a  sound  is  excited  in  the  water,  the  sonorous  undulations  are  more  intense 
in  the  water  near  the  surface  of  the  vessel  containing  it,  than  in  other 
parts  of  the  water  equally  distant  from  the  point  of  origin  of  the  sound; 
thus  we  may  conclude  that,  cceteris  loarihus,  the  sonorous  undulations  of 
solid  bodies  act  with  greater  intensity  than  those  of  water.  Hence,  we 
perceive  at  once  an  important  use  of  the  cochlea. 

This  is  not,  however,  the  sole  office  of  the  cochlea;  the  spiral  lamina, 
as  well  as  the  membranous  labyrinth,  receives  sonorous  impulses  through 
the  medium  of  the  fluid  of  the  labyrinth  from  the  cavity  of  the  vestibule, 
and  from  the  fenestra  rotunda.  The  lamina  spiralis  is,  indeed,  much 
better  calculated  to  render  the  action  of  tliese  undulations  upon  the  audi- 
tory nerve  efficient,  than  the  membranous  labyrinth  is;  for  as  a  solid  body 
insulated  by  a  different  medium,  it  is  capable  of  resonance. 

The  rodx  of  Corti  are  probably  arranged  so  that  each  is  set  to  vibrate 
in  unison  witli  a  particular  tone,  and  thus  strike  a  particular  note,  the 
sensation  of  which  is  carried  to  the  brain  by  those  filaments  of  the  audi- 
tory nerve  with  wliich  the  little  vibrating  rod  is  connected.  The  distinc- 
tive function,  therefore,  of  these  minute  bodies  is,  probably,  to  render 


THE  SENSES. 


193 


sensible  to  the  brain  the  various  musical  notes  and  tones,  one  of  them 
answering  to  one  tone,  and  one  to  another;  while  perhaps  the  other  parts 
of  the  organ  of  hearing  discriminate  between  the  intensities  of  different 
sounds,  rather  than  their  qualities. 

"In  the  cochlea  we  have  to  do  with  a  series  of  apparatus  adapted  for 
performing  sympathetic  vibrations  with  wonderful  exactness.  We  have 
here  before  us  a  musical  instrument  which  is  designed,  not  to  create 
musical  sounds,  but  to  render  them  perceptible,  and  which  is  similar 
in  construction  to  artificial  musical  instruments,  but  which  far  surpasses 
them  in  the  delicacy  as  well  as  the  simplicity  of  its  execution.  For,  while 
in  a  piano  every  string  must  have  a  separate  hammer  ^  means  of  which 
it  is  sounded,  the  ear  possesses  a  single  hammer  of  an  ingenious  form  in  its 
ear-bones,  which  can  make  every  string  of  the  organ  of  Corti  sound  sepa- 
rately.^^ (Bernstein.) 

About  3000  rods  of  Corti  are  present  in  the  human  ear;  this  would 
give  about  400  to  each  of  the  seven  octaves  which  are  within  the  compass 
of  the  ear.  Thus  about  32  would  go  to  each  semi-tone.  Weber  asserts 
that  accomplished  musicians  can  appreciate  differences  in  pitch  as  small 
as  "eVth  of  a  tone.  Thus  on  the  theory  above  advanced,  the  delicacy  of 
discrimination  would,  in  this  case,  appear  to  have  reached  its  limits. 

Sensibility  of  the  Auditory  Nerve. — Any  elastic  body,  e.g.,  air,  a 
membrane,  or  a  string  performing  a  certain  number  of  regular  vibrations 
in  the  second,  gives  rise  to  what  is  termed  a  musical  sound  or  tone.  We 
must,  however,  distinguish  between  a  musical  sound  and  a  mere  noise; 
the  latter  being  due  to  irregular  vibrations. 

•  Qualities  of  Musical  Sound. — Musical  sounds  are  distinguished 
from  each  other  by  three  qualities.  1.  Strength  or  intensity,  which  is 
due  to  the  amplitude  or  length  of  the  vibrations.  2.  Fitch,  which  de- 
pends upon  the  number  of  vibrations  in  a  second.  3.  Quality,  Color,  or 
Timbre.  It  is  by  this  property  that  we  distinguish  the  same  note  sounded 
on  two  instruments,  e.^.,  a  piano  and  a  flute.  It  has  been  proved  by 
Helmholtz  to  depend  on  the  number  of  secondary  notes,  termed  har- 
monics, which  are  present  with  the  predominating  or  fundamental  tone. 

It  would  appear  that  two  impulses,  which  are  equivalent  to  four  single 
or  half  vibrations,  are  sufficient  to  produce  a  definite  note,  audible  as 
such  through  the  auditory  nerve.  The  note  produced  by  the  shocks  of 
the  teeth  of  a  revolving  wheel,  at  regular  intervals  upon  a  solid  body,  is 
still  heard  when  the  teeth  of  the  wheel  are  removed  in  succession,  until 
two  only  are  left;  the  second  produced  by  the  impulse  of  these  two  teeth 
has  still  the  same  definite  value  in  the  scale  of  music. 

The  maximum  and  minimum  of  the  intervals  of  successive  impulses 
still  appreciable  through  the  auditory  nerve  as  determinate  sounds,  have 
been  determined  by  M.  Savart.  If  their  intensity  is  sufficiently  great, 
sounds  are  still  audible  which  result  from  the  succession  of  48,000  half 
Vol.  II.— 13. 


194 


HAND-BOOK  OF  PHYSIOLOGY. 


vibrations,  or  24,000  impulses  in  a  second;  and  this,  probably,  is  not  the 
extreme  limit  in  acuteness  of  sounds  perceptible  by  the  ear.  For  the  op- 
posite extreme,  he  has  succeeded  in  rendering  sounds  audible  which  were 
produced  by  only  fourteen  or  eighteen  half  vibrations,  or  seven  or  eight 
impulses  in  a  second;  and  sounds  still  deeper  might  probably  be  heard, 
if  the  individual  impulses  could  be  sufficiently  prolonged. 

By  removing  one  or  several  teeth  from  the  toothed  wheel  the  fact  has 
been  demonstrated  that  in  the  case  of  the  auditory  nerve,  as  in  that  of 
the  optic  nerve,  the  sensation  continues  longer  than  the  impression  which 
causes  it;  for  a  removal  of  a  tooth  fron\  the  wheel  produced  no  interrup- 
tion of  the  sounds  The  gradual  cessation  of  the  sensation  of  sound  ren- 
ders it  difficult,  however,  to  determine  its  exact  duration  beyond  that  of 
the  impression  of  the  sonorous  impulses. 

Direction  of  Sounds. — The  power  of  perceiving  the  direction  of 
sounds  is  not  a  faculty  of  the  sense  of  hearing  itself,  but  is  an  act  of  the 
mind  judging  on  experience  previously  acquired.  From  the  modifications 
which  the  sensation  of  sound  undergoes  according  to  the  direction  in 
which  the  sound  reaches  us,  the  mind  infers  the  position  of  the  sounding 
body.  The  only  true  guide  for  this  inference  is  the  more  intense  action 
of  the  sou  ad  upon  one  than  upon  the  other  ear.  But  even  here  there  is 
room  for  much  deception,  by  the  influence  of  reflexion  or  resonance,  and 
by  the  propagation  of  sound  from  a  distance,  without  loss  of  intensity, 
through  curved  conducting  tubes  filled  with  air.  By  means  of  such  tubes, 
or  of  solid  conductors,  which  convey  the  sonorous  vibrations  from  their 
source  to  a  distant  resonant  body,  sounds  may  be  made  to  appear  to 
originate  in  a  new  situation.  The  direction  of  sound  may  also  be  judged 
of  by  means  of  one  ear  only;  the  position  of  the  ear  and  head  being- 
varied,  so  that  the  sonorous  undulations  at  one  moment  fall  upon  the  ear 
in  a  perpendicular  direction,  at  another  moment  obliquely.  But  when 
neither  of  these  circumstances  can  guide  us  in  distinguishing  the  direction 
of  sound,  as  when  it  falls  equally  upon  both  ears,  its  source  being,  for 
example,  either  directly  in  front  or  behind  us,  it  becomes  impossible  to 
determine  whence  the  sound  comes. 

Distance  of  Sounds. — The  distance  of  the  source  of  sounds  is  not 
recognized  by  the  sense  itself,  but  is  inferred  from  their  intensity.  The 
sound  itself  is  always  seated  but  in  one  place,  namely,  in  our  ear;  but  it 
is  interpreted  as  coming  from  an  exterior  soniferous  body.  When  the  in- 
tensity of  the  voice  is  modified  in  imitation  of  the  effect  of  distance,  it 
excites  the  idea  of  its  originating  at  a  distance.  Ventriloquists  take 
advantage  of  the  difficulty  with  which  the  direction  of  sound  is  recognized, 
and  also  the  influence  of  the  imagination  over  our  judgment,  when  they 
direct  their  voice  in  a  certain  direction,  and  at  the  same  time  pretend, 
themselves,  to  hear  the  sounds  as  coming  from  thence. 

The  effect  of  the  action  of  sonorous  undulations  u])oii  the  nerve  of 


THE  SENSES. 


195 


hearirjg,  endures  someAvhat  longer  than  the  period  during  which  the  un- 
dulations are  passing  through  the  ear.  If,  however,  the  impressions  of 
the  same  sound  be  very  long  continued,  or  constantly  repeated  for  a  long 
time,  then  the  sensation  produced  may  continue  for  a  very  long  time, 
more  than  twelve  or  twenty-four  hours  even,  after  the  original  cause  of 
the  sound  has  ceased. 

Binaural  Sensations. — Corresponding  to  the  double  vision  of  the 
same  object  with  the  two  eyes,  is  the  double  hearing  with  the  two  ears; 
and  analogous  to  the  double  vision  with  one  eye,  dependent  on  unequal 
refraction,  is  the  double  hearing  of  a  single  sound  with  one  ear,  owing  to 
the  sound  coming  to  the  ear  through  media  of  unequal  conducting  power. 
The  first  kind  of  double  hearing  is  very  rare;  instances  of  it  are  recorded, 
however,  by  Sauvages  and  Itard.  The  second  kind,  which  depends  on 
the  unequal  conducting  power  of  two  media  through  which  the  same 
sound  is  transmitted  to  the  ear,  may  easily  be  experienced.  If  a  small 
bell  be  sounded  in  water,  while  the  ears  are  closed  by  plugs,  and  a  solid 
conductor  be  interposed  between  the  water  and  the  ear,  two  sounds  will 
be  heard  differing  in  intensity  and  tone;  one  being  conveyed  to  the  ear 
through  the  medium  of  the  atmosphere,  the  other  through  the  conduct- 
ing-rod. 

Subjective  Sensations  of  Sound. — Subjective  sounds  are  the  result 
of  a  state  of  irritation  or  excitement  of  the  auditory  nerve  produced  by 
other  causes  than  sonorous  impulses.  A  state  of  excitement  of  this 
nerve,  however  induced,  gives  rise  to  the  sensation  of  sound.  Hence  the 
ringing  and  buzzing  in  the  ears  heard  by  persons  of  irritable  and  exhausted 
nervous  system,  and  by  patients  with  cerebral  disease,  or  disease  of  the 
auditory  nerve  itself;  hence  also  the  noise  in  the  ears  heard  for  some 
time  after  a  long  journey  in  a  rattling  noisy  vehicle.  Ritter  found  that 
electricity  also  excites  a  sound  in  the  ears.  From  the  above  truly  subjec- 
tive sound  we  must  distinguish  those  dependent,  not  on  a  state  of  the 
auditory  nerve  itself  merely,  but  on  sonorous  vibrations  excited  in  the 
auditory  apparatus.  Such  are  the  buzzing  sounds  attendant  on  vascular 
congestion  of  the  head  and  ear,  or  on  aneurismal  dilatation  of  the  vessels. 
Frequently  even  the  simple  pulsatory  circulation  of  the  blood  in  the  ear 
is  heard.  To  the  sounds  of  this  class  belong  also  the  buzz  or  hum  heard 
during  the  contraction  of  the  palatine  muscles  in  the  act  of  yawning; 
during  the  forcing  of  air  into  the  tympanum,  so  as  to  make  tense  the 
membrana  tympani;  and  in  the  act  of  blowing  the  nose,  as  well  as  dur- 
ing the  forcible  depression  of  the  lower  jaw. 

Irritation  or  excitement  of  the  auditory  nerve  is  capable  of  giving  rise 
to  movements  in  the  body,  and  to  sensations  in  other  organs  of  sense. 
In  both  cases  it  is  probable  that  the  laws  of  reflex  action,  through  the 
medium  of  the  brain,  came  into  play.  An  intense  and  sudden  noise  ex- 
cites, in  every  person,  closure  of  the  eyelids,  and,  in  nervous  individuals. 


HAND-BOOK  OF  PHYSIOLOGY. 


a  start  of  the  whole  body  or  an  unpleasant  sensation,  like  that  produced 
by  an  electric  shock,  throughout  the  body,  and  sometimes  a  particular 
feeling  in  tlie  external  ear.  Various  sounds  cause  in  many  people  a  dis- 
agreeable feeling  in  the  teeth,  or  a  sensation  of  cold  tickling  through  the 
body,  and,  in  some  people,  intense  sounds  are  said  to  make  the  saliva 
collect. 

.Sight. 

Eyelids  and  Lachrymal  Apparatus. — The  eyelids  consist  of  two 
movable  folds  of  skin,  each  of  which  is  kept  in  shape  by  a  thin  plate  of 
yellow  elastic  tissue.  Along  their  free  edges  are  inserted  a  number  of 
curved  hairs  {eyelashes),  Avhich,  when  the  lids  are  half  closed,  serve  to 
protect  the  eye  from  dust  and  other  foreign  bodies:  their  tactile  sensibil- 
ity is  also  very  delicate. 


Fig.  365. 


On  the  inner  surface  of  the  elastic  tissue  are  disposed  a  number  of 
small  racemose  glands  (Meibomian),  whose  ducts  open  near  the  free  edge 
of  the  lid. 

The  orbital  surface  of  each  lid  is  lined  by  a  delicate,  highly  sensitive 
mucous  membrane  {cojijuiictiva),  which  is  continuous  witli  the  skin  at 
the  free  edge  of  each  lid,  and  after  liiiing  the  inner  surface  of  the  eyelid 
is  reflected  on  to  the  - eyeball,  being  somewhat  loosely  adlierent  to  the 
sclerotic  coat.  The  epithelial  layer  is  continued  over  the  cornea  at  its. 
anterior  epithelium.  At  the  inner  edge  of  the  eye  the  conjunctiva 
becomes  continuous  with  the  mucous  lining  of  the  laclirymal  sac  and 
duct,  Avhich  again  is  continuous  with  tlio  mucous  nu^mbrane  of  the  in- 
ferior meatus  of  tlic  nose. 


THE  SENSES. 


197 


The  laclirymal  gland  is  lodged  in  the  upper  and  outer  angle  of  the 
orbit.  Its  secretion,  which  issues  from  several  ducts  on  the  iuner  surface 
of  the  upper  lid,  under  ordinary  circumstances  just  suffices  to  keep  the 
conjunctiva  moist.  It  passes  out  through  two  small  openings  (pun eta 
lachrymalia)  near  the  inner  angle  of  the  eye,  one  in  each  lid,  into  the 
lachrymal  sac,  and  thence  along  the  nasal  duct  into  the  inferior  meatus 
of  the  nose.  The  excessive  secretion  poured  out 
under  the  influence  of  any  irritating  vapor  or  pain- 
ful emotion  overflows  the  lower  lid  in  the  form  of 
tears. 

The  eyelids  are  closed  by  the  contraction  of  a 
sphincter  muscle  {orUcularis),  supplied  by  the 
Facial  nerve;  the  upper  lid  is  raised  by  the  Levator 
palpelrce  stiperioris,  which  is  supplied  by  the 
Third  nerve. 

The  Eyeball. 

The  eyeball  or  the  organ  of  vision  (Fig.  365) 
consists  of  a  variety  of  structures  which  may  be 
thus  enumerated: — 

The  sclerotic,  or  outermost  coat,  envelopes 
about  five-sixths  of  the  eyeball:  continuous  wdth 
it,  in  front,  and  occupying  the  remaining  sixth,  is 
the  cornea.  Immediately  within  the  sclerotic  is 
the  choroid  coat,  and  within  the  choroid  is  the 
retina.  The  interior  of  the  eyeball  is  well-nigh 
filled  by  the  aqueous  and  vitreous  humors  and 
the  crystalline  lens;  but,  also,  there  is  suspended 
in  the  interior  a  contractile  and  perforated  cur- 
tain,— the  iris,  for  regulating  the  admission  of 
light,  and  behind  the  junction  of  the  sclerotic 
and  cornea  is  a  ciliary  muscle,  the  function  of 
which  is  to  adapt  the  eye  for  seeing  objects  at 
various  distances. 

Structure  of  Sclerotic. — The  sclerotic  coat 
is  composed  of  connective  tissue,  arranged  in  vari- 
ously disposed  and  inter-communicating  layers.  It 
is  strong,  tough,  and  opaque,  and  not  very  elastic. 

Structure  of  Cornea. — The  cornea  is  a  transparent  membrane  which 
forms  a  segment  of  a  smaller  sphere  than  the  rest  of  the  eyeball,  and  is 
let  in,  as  it  were,  into  the  sclerotic  with  which  it  is  continuous  all  round. 
It  is  coated  with  a  laminated  anterior  epithelium  {a,  Fig.  367)  consisting 
of  seven  or  eight  layers  of  cells,  of  which  the  superficial  ones  are  fiattened 


Fig.  366.— Vertical  sectionof 
rabbit's  cornea,  stained  with 
gold  chloride,  e,  Laminated 
anterior  epithelium.  Imme- 
diately beneath  this  is  the  an- 
terior elastic  lamina  of  Bow- 
man, n.  Nerves  forming  a 
delicate  sub-epithelial  plexus, 
and  sending  up  fine  twigs  be- 
tween the  epithelial  cells  to 
end  in  a  second  plexus  on  the 
free  surface;  d,  Descemefs 
membrane,  consisting  of  a 
fine  elastic  layer,  and  a  single 
layer  of  epitheUal  cells;  the 
substance  of  the  cornea,  /,  is 
seen  to  be  fibrillated,  and  con- 
tains many  layers  of  branched 
coi-puscles,  arranged  parallel 
to  the  free  surface,  and  here 
seen  edgewise.  (Schofield.) 


198 


HAND-BOOK  OF  PHYSIOLOGY. 


1 


and  scaly,  and  the  deeper  ones  more  or  less  columnar.  Immediately 
beneath  this  is  the  anterior  elastic  lamina  (Bowman). 

The  cornea  tissue  proper  as  well  as  its  epithelium  is,  in  the  adult, 
completely  d3stitute  of  blood-vessels;  it  consists  of  an  intercellular  ground- 
substance  of  rather  obscurely  fibrillated  flattened  bundles  of  connective 
tissue,  arranged  parallel  to  the  free  surface,  and  forming  the  boundaries 


Fig.  367.— Vertical  section  of  rabbit's  cornea,  a,  Anterior  epithelium,  sho-vving  the  different  shapes 
of  the  cells  at  various  depths  from  the  free  surface;  6,  portion  of  the  substance  of  cornea.  (Klein.) 

of  branched  anastomosing  spaces  in  which  the  cornea-corpuscles  lie.  These 
branched  cornea-corpuscles  have  been  seen  to  creep  by  amoeboid  move- 
ment from  one  branched  space  into  another.  At  its  posterior  surface  the 
cornea  is  limited  by  the  posterior  elastic  lamina,  or  membrane  of  Descemet, 
the  inner  layer  of  which  consists  of  a  single  stratum  of  epithelial  cells 
(Fig.  366,  d). 

Nerves  of  Cornea. — The  nerves  of  the  cornea  are  both  large  and 
numerous:  they  are  derived  from  the  ciliary  nerves.    They  traverse  the 


Fig.  368.— Horizontal  preparation  of  cornea  of  frog;  showing  the  nefrn^ork  of  branched  cornea 
corpuscles.   The  ground  substance  is  completely  colorless.    X  400.  (Klein.) 

substance  of  the  cornea,  in  which  some  of  them  terminate,  in  the  direc- 
tion of  its  anterior  surface,  near  which  the  axis  cylinders  break  up  into 
bundles  of  very  delicate  beaded  fibrilla'  (Fig.  3(56):  tliese  form  a  plexus 
immediately  beneath  the  epithelium,  from  which  delicate  librils  pass  up 


THE  SENSES. 


199 


between  the  cells  anastomosing  with  horizontal  branches,  and  forming  a 
deep  intra-epithelial  plexus,  from  which  fibres  ascend,  till  near  the  surface 
they  form  a  superficial  intra-epithelial  network. 

Structure  of  Choroid  {tunica  vasculosa). — This  coat  of  the  eye- 
ball is  formed  by  a  very  rich  network  of  capillaries  (chorio-capillaris)  out- 
side which  again  are  connective-tissue  layers  of  stellate  pigmented  cells 
(Fig.  25)  with  numerous  arteries  and  veins. 

The  choroid  coat  ends  in  front  in  what  are  called  the  ciliary  processes 
(Fig.  365). 

Structure  of  Retina. — The  retina  (Fig.  370)  is  a  delicate  mem- 
brane, concave,  with  the  concavity  directed  forward  and  ending  in  front, 
near  the  outer  part  of  the  ciliary  processes  in  a  finely  notched  edge, — the 
ora  serrata.  Semi-transparent  when  fresh,  it  soon  becomes  clouded  and 
opaque,  with  a  pinkish  tint  from  the  blood  in  its  minute  vessels.  It  results 
from  the  sudden  spreading  out  or  expansion  of  the  optic  nerve,  of  whose 
terminal  fibres,  apparently  deprived  of  their  external  white  substance, 
together  with  nerve  cells,  it  is  essentially  composed. 


Fig.  369.— Surface  view  of  part  of  lamella  of  kitten's  cornea,  prepared  first  with  caustic  potash 
and  then  with  nitrate  of  silver.  (By  this  method  the  branched  cornea-corpuscles  with  their  granular 
protoplasm  and  large  oval  nuclei  are  brought  out.)    x  450.   (Klein  and  Noble  Smith.) 

Exactly  in  the  centre  of  the  retina,  and  at  a  point  thus  corresponding  to 
the  axis  of  the  eye  in  which  the  sense  of  vision  is  most  perfect,  is  a  round 
yellowish  elevated  spot,  about  ^  of  an  inch  in  diameter,  having  a  minute 
aperture  at  its  summit,  and  called  after  its  discoverer  the  yelloiu  spot  of 
Scemmering.  In  its  centre  is  a  minute  depression  called  fovea  centralis. 
About  yL  of  ail  inch  to  the  inner  side  of  the  yellow  spot,  and  consequently 
of  the  axis  of  the  eye,  is  the  point  at  which  the  optic  nerve  begins  to 
spread  out  its  fibres  to  form  the  retina.  This  is  the  only  point  of  the 
surface  of  the  retina  from  which  the  power  of  vision  is  absent. 

The  retina  consists  of  certain  nervous  elements  arranged  in  several 
layers,  and  supported  by  a  very  delicate  connective  tissue. 

From  the  nature  of  the  case  there  is  considerable  uncertainty  as  to  the 
character  (nervous  or  connective  tissue)  of  some  of  the  layers  of  the  retina. 
The  following  ten  layers,  from  within  outward,  are  usually  to  be  distin- 
guished in  a  vertical  section  (Figs.  370,  373). 


200 


HAND-BOOK  OF  PHYSIOLOGY. 


1.  Meinhrana  limitans  mterna :  a  delicate  membrane  in  contact  with 
"the  vitreous  humor. 

2.  Fibres  of  orotic  nerve.  This  layer  is  of  very  varying  thickness  in 
different  parts  of  the  retina:  it  consists  chiefly  of  non-medullated  fibres 
which  interlace,  and  some  of  which  are  continuous  with  processes  of  the 
large  nerve-cells  forming  the  next  layer. 


Fig.  370.— Diagram  of  the  retina.  A,  connective  tissue  portion;  13,  nervous  portion  {the  two 
must  be  combined  to  form  the  complete  retina);  a  a,  membrana  limitans  externa;  6,  rods;  c,  cones;  6', 
rod-granule;  c'.  cone-granule;  both  belonging  to  the  external  granule  laj'er:  e,  Miiller's  sustentacular 
fibres,  with  their  nuclei  e';  d,  intergi-anular  layer;/,  internal  granule  layer;  (/.  molecular  layer,  con- 
nective-tissue portion;  a\  molecular  laj^er,  nerve  fibril  portion;  /i,  ganglion  cells;  7i',  their  axis-cylin- 
der process;     nerve-fibre  layer.   (.Max  Schultze.) 

3.  Layer  of  ganglionic  cor])7iscIes,  consisting  of  large  multipolar  nerve- 
cells,  sometimes  forming  a  single  layer.  In  some  parts  of  the  retina, 
especially  near  the  macula  lutea,  this  layer  is  very  thick,  consisting  of 
several  distinct  strata  of  nerve- cells.  These  cells  lie  in  the  spaces  of  a 
connective-tissue  framework. 


THE  SENSES. 


201 


4.  Molecular  layer.  This  presents  a  finely  granulated  appearance.  It 
consists  of  a  punctiform  connective-tissue  traversed  by  numberless  very 
fine  fibrillar  processes  of  the  nerve-cells. 

5.  Internal  granular  layer.  This  consists  chiefly  of  numerous  small 
round  cells  with  a  very  small  quantity  of  protoplasm  surrounding  a  lar^e 
nucleus;  they  are  generally  bipolar,  giving  off  one  process  outward  and 
another  inward.  They  greatly  resemble  the  ganglionic  corpuscles  of  the 
cerebellum  (Fig.  330).  Besides  these  there  are  large  oval  nuclei  {e,  Fig. 
370,  A)  belonging  to  the  sustentacular  connective-tissue  fibres. 

6.  Inter  granular  layer;  which  closely  resembles  the  molecular  layer, 
but  is  much  thinner.  It  consists  of  finely-dotted  connective  tissue  with 
nerve  fibrils. 

7.  External  granular  layer;  which  consists  of  several  strata  of  small 
cells  resembling  those  of  the  internal  granular  layer;  they  have  been 


Fig.  371.— Ciliary  processes,  as  seen  from  behind.  1,  posterior  surface  of  the  iris,  with  the 
sphincter  muscle  of  the  pupil;  2,  anterior  part  of  the  choroid  coat;  3,  one  of  the  ciliary  processes,  of 
which  about  seventy  are  represented,  y^. 

Fig.  372.— The  posterior  half  of  the  retina  of  the  left  eye,  viewed  from  before;  s.  the  cut  edge  of 
the  sclerotic  coat;  c7t,  the  choroid;  r,  the  retina;  in  the  interior  at  the  middle,  the  macula  lutea  with 
the  depression  of  the  fovea  centralis  is  represented  by  a  slight  oval  shade ;  toward  the  left  side  the 
light  spot  indicates  the  colliculus  or  eminence  at  the  entrance  of  the  optic  nerve,  from  the  centre  of 
which  the  arteria  centralis  is  seen  spreading  its  branches  into  the  retina,  leaving  the  part  occupied  by 
the  macula  comparatively  free.   (After  Henle.) 


classed  as  rod  and  cone  granules,  according  as  they  are  connected  by  very 
delicate  fibrils  with  the  rods  and  cones  respectively.  They  are  lodged 
in  the  meshes  of  a  connective-tissue  framework.  Both  the  internal  and 
external  granular  layer  stain  very  rapidly  and  deeply  with  hsematoxylin, 
while  the  rod  and  cone  layer  remains  quite  unstained. 

8.  Memlrana  limitans  externa;  a  delicate,  well-defined  membrane, 
clearly  marking  the  internal  limit  of  the  rod  and  cone  layer 

9.  Rod  and  cone  layer,  hacillar  layer,  or  membrane  of  Jacob,  consisting 
of  two  kinds  of  elements:  the  ^'rods,'^  which  are  cylindrical  and  of  uni- 
form diameter  throughout,  and  the  ^ 'cones,''  whose  internal  portion  is 


Fig.  371. 


Fig.  372. 


202 


HAND-BOOK  OF  PHYSIOLOGY. 


distinctly  conical,  and  surmounted  externally  by  a  thin  rod-like  body. 
According  to  the  researches  of  Max  Schultze,  the  rods  show  traces  of 
longitudinal  fibrillation,  and,  moreover,  have  a  great  tendency  to  break 
up  into  a  number  of  transverse  discs  like  a  pile  of  coins. 

In  the  rod  and  cone  layer  of  birds,  the  cones  usually  predominate 
largely  in  number,  whereas  in  man  the  rods  are  by  far  the  more  numer- 
ous. In  nocturnal  birds,  however,  such  as  the  owl,  only  rods  are  present, 
and  the  same  appears  to  be  the  case  in  many  nocturnal  and  burrowing 
mammalia,  e.g.,  bat,  hedge-hog,  mouse,  and  mole. 


Fig.  373.— Section  of  the  retina,  choroid,  and  part  of  the  sclerotic,  moderately  magnified,  a, 
membrana  limitans  interna;  &,  nerve-fibre  Jaj-er  ti-aversed  hy  Miiller's  sustentacular  fibres  (of  the 
connective  tissue  system);  c,  ganglion-cell  layer:  c7,  molecular  laj-er;  e,  internal  granular  layer;/, 
intergranular  layer ;(/,  external  granular  laj'er;  h,  membrana  limitans  externa,  running  along  the 
lower  part  of  t,  the  layer  of  rods  and  cones :  pigment  cell  laj-er  formerly  described  as  part  of  the 
choroid;  internal  and  external  vascular  portions  of  the  choroid,  the  first  containing  capillaries, 
the  second  larger  blood-vessels,  cut  in  transverse  section;  n,  sclerotic.   (W.  Pye.) 

10.  Pigment  cell  layer,  which  was  formerly  considered  part  of  the 
choroid.  , 

In  the  centre  of  the  yellow  spot  (macula  lutea),  all  the  layers  of  the 
retina  become  greatly  thinned  out  and  almost  disappear,  except  the  rod 
and  cone  layer,  which  considerably  increases  in  thickness,  and  comes  to 
Qonsists  almost  entirely  of  long  slender  cones,  the  rods  being  very  few  in 
number,  or  entirely  absent.  There  are  capillaries  here,  but  none  of  the 
larger  branches  of  the  retinal  arteries. 


With  regard  to  the  connection  of  tlie  various  layers  there  is  still  some 
uncertainty.    Fig.  370  rc[)reseiits  the  view  of  Max  Schultzc.  According 


THE  SENSES. 


to  this  there  are  certain  sustentacular  fibres  of  connective  tissue  (radiating 
fibres  of  Miiller)  which  spring  from  the  nmnhranal  imitans  interna  almost 
vertically^  and  traverse  the  retina  to  the  limitans  externa,  whence  very 
delicate  connective  tissue  processes  pass  up  between  the  rods  and  cones. 
The  framework  which  they  form  is  represented  in  Fig.  370,  A.  The  nerv- 
ous elements  of  the  retina  are  represented  in  Fig.  370,  B,  and  consist  of 
delicate  fibres  passing  up  from  the  nerve-fibre  layer  to  the  rods  and  cones, 
and  connected  with  the  ganglionic  corpuscles  and  granules  of  the  internal 
and  external  layer. 

Blood-vessels  of  the  Eyeball.— The  eye  is  very  richly  supplied 
with  blood-vessels.  In  addition  ro  the  conjunctival  vessels  which  are 
derived  from  the  palpebral  and  lachrymal  arteries,  there  are  at  least  two 
other  distinct  sets  of  vessels  supplying  the  tunics  of  the  eyeball.  (1)  The 
vessels  of  the  sclerotic,  choroid,  and  iris,  and  (2)  The  vessels  of  the  retina. 

(1.)  These  are  the  short  and  long  posterior  ciliary  arteries  which  pierce 
the  sclerotic  in  the  posterior  half  of  the  eyeball,  and  the  anterior  ciliary 
which  enter  near  the  insertions  of  the  recti.  These  vessels  anastomose 
and  form  a  very  rich  choroidal  plexus;  they  also  supply  the  iris  and  cili- 
ary processes,  forming  a  very  highly  vascular  circle  round  the  outer  mar- 
gin of  the  iris  and  adjoining  portion  of  the  sclerotic. 

The  distinctness  of  these  vessels  from  those  of  the  conjunctiva  is  well 
seen  in  the  difference  between  the  bright  red  of  blood-shot  eyes  (con- 
junctival congestion),  and  the  pink  zone  surrounding  the  cornea  which 
indicates  deep-seated  ciliary  congestion. 

(2.)  retinal  vessels  (Fig.  372)  are  derived  from  the  arteria  cen- 
tralis retinae,  which  enters  the  eyeball  along  the  centre  of  the  optic  nerve. 
They  ramify  all  over  the  retina,  chiefly  in  its  inner  layers.  They  can  be 
seen  by  direct  ophthalmoscopic  examination. 

Optical  Appaeatus. 

The  eye  may  be  compared  to  the  camera  used  by  photographers  formed 
by  a  convex  lens.  In  this  instrument  images  of  external  objects  are 
thrown  upon  a  ground-glass  screen  at  the  back  of  a  box,  the  interior  of 
which  is  painted  black.  In  the  eye  the  convex  lens  is  represented  by  the 
crystalline  lens,  the  dark  box  by  the  eyeball  with  its  choroidal  pigment, 
and  the  screen  by  the  retina.  In  the  case  of  the  camera  the  screen  is 
enabled  to  receive  clear  images  of  objects  at  different  distances,  by  being 
shifted  forward  and  back:  while  the  convex  lens  too  can  be  screwed  in 
and  out.  The  corresponding  contrivance  in  the  eye  will  be  described 
under  the  head  of  Accommodation. 

Conditions  Necessary.— The  essential  constituents  of  the  optical 
apparatus  of  the  eye  may  be  thus  enumerated:  (1)  A  nervous  structure 
(the  retina)  to  be  stimulated  by  light  and  to  transmit  by  means  of  the 
optic  nerve,  of  which  it  is  the  terminal  expansion,  the  impression  of  the 
stimulation  to  the  brain,  in  which  it  excites  the  sensation  of  vision;  (2) 


204  HAND-BOOK  OF  rilYSIOLOGY. 

An  aj)])aratus  consisting  of  certain  refractory  media,  cornea,  crystalline 
lens,  aqueous  and  vitreous  humor,  the  function  of  which  is  to  collect 
together  into  one  point  the  dillerent  divergent  rays  emitted  by  each  point 
of  every  external  body  and  of  giving  them  such  directions  that  they  are 
exactly  focussed  upon  the  retina,  and  thus  produce  an  exact  image  of 
the  object  from  which  they  proceed.  For  as  light  radiates  from  a  lu- 
minous body  in  all  directions,  when  the  media  offer  no  impediment  to 
its  transmission,  a  luminous  point  will  necessarily  illuminate  all  parts 
of  a  surface,  such  as  the  retina  opposed  to  it,  and  not  merely  one  single 
point.  A  retina,  therefore,  without  any  optical  apparatus  placed  in 
front  of  it  to  separate  the  light  of  different  objects,  would  not  allow  of 
distinct  vision,  but  would  merely  transmit  such  a  general  impressioii  of 
daylight  as  would  distinguish  it  from  the  night;  (3)  A  contractile  dia- 
pliragm  (iris)  with  a  central  aperture  for  regulating  the  quantity  of  light 
admitted  into  the  eye;  and  (4)  a  contractile  structure  (ciliary  muscle), 
an  arrangement  by  which  the  chief  refracting  medium  (crystalline  lens) 
shall  be  so  controlled  as  to  enable  objects  to  be  seen  at  various  distances, 
causing  convergence  of  the  rays  of  light  that  fall  upon  and  traverse  it 
(accommodation) . 

Eefeactixg  Media. 

Of  the  refracting  media  the  cornea  is  in  a  twofold  manner  capable  of 
refracting  and  causing  convergence  of  the  rays  of  light  that  fall  upon 
and  traverse  it.  It  thus  affects  them  first,  by  its  density;  for  it  is  a  law 
in  optics  that  when  rays  of  light  pass  from  a  rarer  into  a  denser  medium, 
if  they  impinge  upon  the  surface  in  a  direction  removed  from  the  per- 
pendicular, they  are  bent  out  of  their  former  direction  toward  that  of  a 
line  perpendicular  to  the  surface  of  the  denser  medium;  and,  secondly, 
by  its  convexity;  since  rays  of  light  impinging  upon  a  convex  transparent 
surface,  are  refracted  toward  the  centre,  those  being  most  refracted  which 
are  farthest  from  the  centre  of  the  convex  surface. 

Behind  the  cornea  is  a  space  containing  a  thin  watery  fluid,  the  aque- 
ous Jmmor,  holding  in  solution  a  small  quantity  of  sodium  chloride  and 
extractive  matter.  The  space  containing  the  aqueous  humor  is  divided 
into  an  anterior  and  posterior  chamber  by  a  membranous  partition,  the 
iris,  to  be  presently  again  mentioned.  The  effect  produced  by  the  aque- 
ous humor  on  the  rays  of  light  traversing  it,  is  not  yet  fully  ascertained. 
Its  chief  use,  probably,  is  to  assist  in  filling  the  eyeball,  so  as  to  main- 
tain its  proper  convexity,  and  at  the  same  time  to  furnish  a  medium  in 
which  the  movements  of  the  iris  can  take  place. 

Behind  the  aqueous  humor  and  the  iris,  and  imbedded  in  the  anterior 
part  of  tlie  nuHlium  next  to  be  described,  viz.,  the  vitreous  lunnor.  is  seated 
a,  doubly-convex  body,  the  crystalline  lens,  which  is  the  most  important 


THE  SENSES. 


205 


Fig.  374.— Laminated  structure 
of  the  crystalline  lens.  The 
laminae  are  split  up  after  harden- 
ing in  alcohol.  1 ,  the  denser  cen- 
tral part  or  nucleus;  2,  the  suc- 
cessive external  layers.  A-  (Ar- 
nold.) 1 


refracting  structure  of  the  eye.  The  structure  of  the  lens  is  very  complex. 
It  consists  essentially  of  fibres  united  side  by  side  to  each  other,  and 
arranged  together  in  very  numerous  laminae,  which  are  so  placed  upon 
one  another,  that  when  hardened  in  spirit  the  lens  splits  into  three  por- 
tions in  the  form  of  sectors,  each  of  which  is  composed  of  suyjerimposed 
concentric  laminae.  The  lens  increases  in  density  and,  consequently,  in 
power  of  refraction,  from  without  inward;  the 
central  part,  usually  termed  the  nucleus,  being 
the  most  dense. 

The  vitreous  humor  constitutes  nearly  four- 
fifths  of  the  whole  globe  of  the  eye.  It  fills 
up  the  space  between  the  retina  and  the  lens, 
and  its  soft  jelly-like  substance  consists  essen- 
tially of  numerous  layers,  formed  of  delicate, 
simple  membrane,  the  spaces  between  which 
are  filled  with  a  watery,  pellucid  fluid.  Its 
principal  use  appears  to  be  that  of  giving  the 
proper  distension  to  the  globe  of  the  eye,  and 
of  keeping  the  surface  of  the  retina  at  a  proper 
distance  from  the  lens. 

Action  of  the  Iris. — The  iris  is  a  vertically -placed  membranous  dia- 
phragm, provided  with  a  central  aperture,  the  pupil,  for  the  transmission 
of  light.  It  is  composed  of  plain  muscular  fibres  imbedded  in  ordinary 
fibro-cellular  or  connective  tissue.  The  muscular  fibres  have  a  direction, 
for  the  most  part,  radiating  from  the  circumference  toward  the  pupil;  but 
as  they  approach  the  pupillary  margin,  they  assume  a  circular  direction, 
and  at  the  very  edge  form  a  complete  ring.  By  the  contraction  of  the 
radiating  fibres  (dilator  pupillse)  the  size  of  the  pupil  is  enlarged:  by  the 
contraction  of  the  circular  ones  (sphincter  pupillae),  it  is  diminished.  The 
object  effected  by  the  movements  of  the  iris,  is  the  regulation  of  the 
quantity  of  light  transmitted  to  the  retina.  The  posterior  surface  of  the 
iris  is  coated  with  a  layer  of  dark  pigment,  so  that  no  rays  of  light  can 
pass  to  the  retina,  except  such  as  are  admitted  through  the  aperture  of 
the  pupil. 

This  iris  is  very  richly  supplied  with  nerves  and  blood-vessels.  Its 
circular  muscular  fibres  are  supplied  by  the  third  (by  the  short  ciliary 
branches  of  the  ophthalmic  ganglion),  and  its  radiating  fibres,  by  the  sym- 
pathetic and  fifth  cranial  nerve  (by  the  long  ciliary  branches  of  the  nasal 
nerve). 

Contraction  of  the  pupil  occurs  under  the  following  circumstances:  (1) 
On  exposure  of  the  eye  to  a  bright  light;  (2)  when  the  eye  is  focussed  for 
near  objects;  (3)  when  the  eyes  converge  to  look  at  a  near  object;  (4)  on 
the  local  application  of  eserine  (active  principle  of  Calabar  bean);  (5)  on 
the  administration  internally  of  opium,  aconite,  and  in  the  early  stages 


206 


HAND-BOOK  OF  PHYSIOLOGY. 


of  chloroform  and  alcohol  poisoning;  (6)  on  division  of  the  cervical  sym- 
pathetic or  stimulation  of  the  third  nerve.  Dilatation  of  the  pupil 
occurs  (1)  in  a  dim  light;  (2)  when  the  eye  isfocussed  for  distant  objects; 
(3)  on  the  local  application  of  atropine  and  its  allied  alkaloids;  (4)  on  the 
internal  administration  of  atropine  and  its  allies;  (5)  in  the  later  stages 
of  poisoning  b}^  chloroform,  opium,  and  other  drugs;  (6)  on  paralysis 
of  the  third  nerve;  (T)  on  stimulation  of  the  cervical  sympathetic,  or  of 
its  centre  in  the  floor  of  tJie  front  of  the  aqueduct  of  Sylvius.  The  con- 
traction of  the  pupil  ai^pears  to  be  uiider  the  control  of  a  centre  in  the 
corpora  quadrigemina,  and  this  is  reflexly  stimulated  by  a  bright  light, 
and  the  dilatation  when  the  reflex  centre  is  not  in  action  is  due  to  the 
more  powerful  sympathetic  action;  but  in  addition,  it  appears  that  both 
contraction  and  dilatation  may  be  produced  by  a  local  mechanism,  upon 
which  certain  drugs  can  act,  which  is  independent  of  and  probably  often 
antagonistic  to  the  action  of  the  central  apparatus  of  the  third  and  sym- 
pathetic nerves.  The  action  of  the  fifth  nerve  upon  the  pupil  is  not  well 
understood,  but  its  apparent  effect  in  producing  dilatation  is  due  to  the 
mixture  of  sjmipathetic  fibres  with  its  nasal  branch.  The  sympathetic  in- 
fluence upon  the  radiating  fibres  is  believed  to  be  conveyed,  not  by  the 
long  ciliary  branches  of  that  nerve,  but  by  the  short  ciliary  branches  from 
the  ophthalmic  ganglion. 

The  close  sympathy  subsisting  between  the  two  eyes  is  nowhere  better 
shown  than  by  the  condition  of  the  pupil.  If  one  eye  be  shaded  by  the 
hand  its  pupil  will  of  course  dilate;  but  the  pupil  of  the  other  eye  will 
also  dilate,  though  it  is  unshaded. 

Ciliary  Muscle. — The  ciliarij  muscle  is  composed  of  plain  muscular 
fibres,  which  form  a  narrow  zone  around  the  interior  of  the  eyeball,  near 
the  line  of  junction  of  the  cornea  with  the  sclerotic,  and  just  behind  the 
outer  border  of  the  iris  (Fig.  365).  The  outermost  fibres  of  this  muscle 
are  attached  in  front  to  the  inner  part  of  the  sclerotic  and  cornea  at  their 
line  of  junction,  and  diverging  somewhat,  are  fixed  to  the  ciliary  pro- 
cesses, and  a  small  portion  of  the  choroid  immediately  behind  them. 
The  inner  fibres  immediately  within  the  preceding,  form  a  circular  zone 
around  th6  interior  of  the  eyeball,  outside  the  ciliarj^  processes.  They 
compose  the  ring  formerly  called  the  ciliary  ligament. 

Accommodation  of  the  Eye. — The  distinctness  of  the  image 
formed  upon  the  retina,  is  mainly  dependent- on  the  rays  emitted  by  each 
luminous  point  of  the  object  being  brought  to  a  perfect  focus  upon  the 
retina.  If  this  focus  occur  at  a  point  either  in  front  of,  or  behind  the 
retina,  indistinctness  of  vision  ensues,  with  the  production  of  a  halo. 

focal  distance,  i.e.,  the  distance  of  the  point  at  which  the  luminous 
rays  from  a  lens  are  collected,  besides  being  regulated  by  the  degree  of 
convexity  and  density  of  the  lens,  varies  with  the  distance  of  the  object 
from  the  lens,  being  greater  as  this  is  shorter,  and  vice  rersd.  Hence, 


THE  SENSES. 


207 


since  objects  placed  at  various  distances  from  the  eye  can,  witliin  a  certain 
range,  different  in  different  persons,  be  seen  with  almost  equal  distinct- 
ness, there  must  be  some  provision  by  which  the  eye  is  enabled  to  adapt 
itself,  so  that  whatever  length  the  focal  distance  may  be,  the  focal  point 
may  always  fall  exactly  upon  the  retina. 

This  power  of  adaptation  of  the  eye  to  vision  at  cliff ereyit  distances  has 
received  the  most  varied  explanations.  It  is  obvious  that  the  effect  might 
be  produced  in  either  of  two  ways,  viz.,  by  altering  the  convexity  or  in- 
tensity, and  thus  the  refracting  power,  either  of  the  cornea  or  lens;  or  by 
changing  the  position  either  of  the  retina  or  of  the  lens,  so  that  whether 
the  object  viewed  be  near  or  distant,  and  the  focal  distance  thus  increased 
or  diminished,  the  focal  point  to  which  the  rays  are  converged  by  the 
lens  may  always  be  at  the  place  occupied  by  the  retina.  The  amount  of 
either  of  these  changes  required  in  even  the  widest  range  of  vision,  is 
extremely  small.  For,  from  the  refractive  powers  of  the  media  of  the 
eye,  it  has  been  calculated  by  Olbers,  that  the  difference  between  the  focal 
distances  of  the  images  ol  an  object  at  such  a  distance  that  the  rays  are 
parallel,  and  of  one  at  the  distance  of  four  inches,  is  only  about  0-143  of 
an  inch.  On  this  calculation,  the  change  in  the  distance  of  the  retina 
from  the  lens  required  for  vision  at  all  distances,  supposing  the  cornea 
and  lens  to  maintain  the  same  form,  would  not 
be  more  than  about  one  line. 

It  is  now  almost  universally  believed  that 
Helmholtz  is  right  in  his  statement  that  the 
immediate  cause  of  the  adaptation  of  the  eye 
for  objects  at  different  distances  is  a  varying 
shape  of  the  lens,  its  front  surface  becoming 
more  or  less  convex,  according  to  the  distance 
of  the  object  looked  at.  The  nearer  the  object, 
the  more  convex  does  the  front  surface  of  the 
lens  become,  and  vice  versa;  the  back  surface 
taking  little  or  no  share  in  the  production  of 
the  effect  required.  The  following  simple  ex- 
periment illustrates  this  point.  If  a  small  flame 
be  held  a  little  to  one  side  of  a  person^s  eye,  an 
observer  looking  at  the  eye  from  the  other  side  sees  three  distinct  images 
of  the  flame  (Fig.  375).  The  first  and  brightest  is  (1)  a  small  erect 
image  formed  by  the  anterior  convex  surface  of  the  cornea:  the  second 
(2)  is  also  erect,  but  larger  and  less  distinct  than  the  preceding,  and  is 
formed  at  the  anterior  convex  surface  of  the  lens:  the  third  (3)  is 
smaller  and  reversed,  it  is  formed  at  the  posterior  surface  of  the  lens, 
which  is  concave  forward,  and  therefore,  like  all  concave  mirrors, 
gives  a  reversed  image.  If  now  the  eye  under  observation  be  made 
to  look  at  a  near  object,  the  second  image  becomes  smaller,  clearer,  and 


Fig.  375.— Diagram  showing 
three  reflections  of  a  candle.  1, 
From  the  anterior  surface  of 
cornea ;  2,  from  the  anterior  sur- 
face of  lens;  3,  from  the  posterior 
surface  of  lens.  For  further  ex- 
planation, see  text.  The  experi- 
ment is  best  performed  by  em- 
ploying an  instrument  invented 
by  Helmholtz,  termed  a  Phako- 
scope. 


208 


HAND-BOOK  OF  PHYSIOLOGY. 


approaches  tlie  first.  If  tlic  c^^e  be  now  adjusted  for  a  far  point,  the 
second  image  enlarges  again,  becomes  less  distinct,  and  recedes  from  the 
first.  In  both  cases  alike  the  first  and  third  images  remain  unaltered  in 
size  and  relative  position.    This  proves  that  during  accommodation  for 


Fig.  376.— Phakoscope  of  Helmholtz.  At  B  B'  are  two  prisms,  by  which  the  h^'ht  t.f  a  candle  is 
concentrated  on  the  eye  of  the  person  experimented  with  at  C;  A  is  tlie  aperture  lor  the  ej'e  of  the 
observer.  The  observer  notices  three  dovible  images,  as  in  Fig.  87.5,  reflected  from  the  e.ye  under  ex- 
amination when  the  eye  is  fixed  upon  a  distant  object:  the  "position  of  the  images  having  been 
noticed,  the  eye  is  then  made  to  focus  a  near  object,  such  as  a  needle  pushed  up  b.v  C;  the  images 
from  the  anterior  sixrface  of  the  lens  will  be  observed  to  move  to^^'ard  each  other,  in  consequence  of 
the  lens  becoming  more  convex. 

near  objects  the  curvature  of  the  cornea,  and  of  the  loosterior  of  the  lens, 
remains  unaltered,  while  the  anterior  surface  of  the  lens  becomes  more 
convex  and  approaches  the  cornea. 


Fig.  377.— Diagram  representing  by  dotted  lines  the  alteration  in  the  shape  of  the  lens,  on  accom- 
modation for  near  objects.   (E.  Landolt.) 


Mechanism  of  Accommodation.— Of  course  ohe  lens  has  no  in- 
herent ])ower  of  contraction,,  and  tliorefore  its  changes  of  outline  must  be 


THE  SENSES. 


209 


produced  by  some  power  from  without;  and  there  seems  no  reason  to 
doubt  that  this  power  is  supplied  by  the  ciliary  muscle.  It  is  sometimes 
termed  the  tensor  choroidem.  As  this  name  implies,  from  its  attachment 
(p.  206,  Vol.  II.),  it  is  able  to  draw  forward  the  choroid,  and  therefore 
slackens  the  tension  of  the  suspensory  ligament  of  the  lens  which  arises 
from  it.  The  lens  is  usually  partly  flattened  by  the  action  of  the  sus- 
pensory ligament;  and  the  ciliary  muscle  by  diminishing  the  tension  of 
this  ligament  diminishes,  to  a  proportional  degree,  the  flattening  of  which 
it  is  the  cause.  On  diminution  or  cessation  of  the  action  of  the  ciliary 
muscle,  the  lens  returns,  in  a  corresponding  degree,  to  its  former  shape, 
by  virtue  of  the  elasticity  of  its  suspensory  ligament  (Fig.  377).  From 
this  it  will  appear  that  the  eye  is  usually  focussed  for  distant  objects.  In 
viewing  near  objects  the  pupil  contracts,  the  opposite  effect  taking  place 
on  withdrawal  of  the  attention  from  near  objects,  and  fixing  it  on  those 
distant. 

Range  of  Distinct  Vision.  Near-point. — In  every  eye  there  is  a 
limit  to  the  power  of  accommodation.  If  a  book  be  brought  nearer  and 
nearer  to  the  eye,  the  type  at  last  becomes  indistinct  and  cannot  be 
brought  into  focus  by  any  effort  of  accommodation,  however  strong. 
This,  which  is  termed  the  near-point,  can  be  determined  by  the  following 
experiment  [Scheijier) .  Two  small  holes  are  pricked  in  a  card  with  a 
pin  not  more  than  a  line  apart,  at  any  rate  their  distance  from  each  other 
must  not  exceed  the  diameter  of  the  pupil.  The  card  is  held  close  in 
front  of  the  eye,  and  a  small  needle  viewed  through  the  pin-holes.  At 


Fig.  378.— Diagram  of  experiment  to  ascertain  the  minimum  distance  of  distinct  vision. 


a  moderate  distance  it  can  be  clearly  focussed,  but  when  brought  nearer, 
beyond  a  certain  point,  the  image  appears  double  or  at  any  rate  blurred. 
This  point  where  the  needle  ceases  to  appear  single  is  the  near-point.  Its-, 
distance  from  the  eye  can  of  course  be  readily  measured.  It  is  usually 
about  5  or  6  inches.  In  the  accompanying  figure  (Fig.  378)  the  lens  1 
represents  the  eye;  ef  the  two  pinholes  in  the  card,  nn  the  retina;  a 
represents  the  position  of  the  needle.  When  the  needle  is  at  a  moderate 
distance,  the  two  pencils  of  light  coming  from  e  and  /,  are  focussed  at  a 
single  point  on  the  retina  nn.  If  the  needle  be  brought  nearer  than  the 
near-point,  the  strongest  effort  of  accommodation  is  not  sufficient  to  focus, 
the  two  pencils,  they  meet  at  a  point  behind  the  retina.  The  effect  is; 
Vol.  II.— 14. 


210 


HAND-BOOK  OF  PHYSIOLOGY. 


the  same  as  if  the  retina  were  shifted  forward  to  mm.  Two  images,  h,  g, 
are  formed,  one  from  each  hole.  It  is  interesting  to  note  that  when  two 
images  are  produced,  the  lower  one  g  really  appears  in  the  position  Q, 
while  the  upper  one  appears  in  the  position  p.  This  may  be  readily 
verified  by  coyering  the  holes  in  succession. 

The  contents  of  the  ball  of  the  eye  are  surrounded  and  kept  in  posi- 
tion by  the  cornea,  and  the  dense,  fibrous  membrane  before  referred  to  as 
the  sclerotic,  which,  besides  thus  encasing  the  contents  of  the  eye,  serves 
to  give  attachment  to  the  yarious  muscles  by  which  the  movements  of 
the  eyeball  are  effected.  These  muscles,  and  the  nerves  supplying  them, 
have  been  already  considered  (p.  138  et  seq..  Vol.  II.). 

Course  of  a  Ray  of  Light. — AVith  the  help  of  the  diagram  (Fig. 
379)  representing  a  vertical  section  of  the  eye  from  before  backward,  the 
mode  in  which,  by  means  of  the  refracting  media  of  the  eye,  an  image 


Fig.  379.— Course  of  a  ray  of  light. 


of  an  object  of  sight  is  thrown  on  the  retina,  may  be  rendered  intelligible. 
The  rays  of  the  cones  of  light  emitted  by  the  points  a  b,  and  every  other 
point  of  an  object  placed  before  the  eye,  are  first  refracted,  that  is,  are 
bent  toward  the  axis  of  the  cone,  by  the  cornea  c  c,  and  the  aqueous 
humor  contained  between  it  and  the  lens.  The  rays  of  each  cone  are 
again  refracted  and  bent  still  more  toward  its  central  ray  or  axis  by  the 
anterior  surface  of  the  lens  e  e;  and  again  as  they  pass  out  through  its 
posterior  surface  into  the  less  dense  medium  of  the  vitreous  humor.  For 
a  lens  has  the  power  of  refracting  and  causing  the  convergence  of  the 
rays  of  a  cone  of  light,  not  only  on  their  entrance  from  a  rarer  medium 
into  its  anterior  convex  surface,  but  also  at  their  exit  from  its  posterior 
convex  surface  into  the  rarer  medium. 

In  this  manner  the  rays  of  the  cones  of  light  issuing  from  the  points 
A  and  B  are  again  collected  to  points  a  and  h\  and,  if  the  retina  f  be 
situated  at  a  and  h,  perfect,  tliough  reversed,  images  of  the  points  a  and 
B  will  be  formed  upon  it:  but  if  tlie  retina  be  not  at  a  and  h,  but  eitlicr 
before  or  behind  that  situation, — for  instance,  at  H  or  G, — circular  lumi- 
nous spots  6'  and  /,  or  e  and     instead  of  points,  will  be  seen;  for  at  ii 


THE  SENSES. 


211 


the  rays  have  not  yet  met,  and  at  g  they  have  already  intersected  each 
other,  and  are  again  diverging. 

The  retina  must  therefore  be  situated  at  the  proper  focal  distance 
from  the  lens,  otherwise  a  defined  image  will  not  be  formed;  or,  in  other 
words,  the  rays  emitted  by  a  given  point  of  the  object  will  not  be  col- 
lected into  a  corresponding  point  of  focus  upon  the  retina. 

Defects  m  the  Appaeatus. 

A.  Defects  in  the  Refracting  Media. — Under  this  head  we  may 
consider  the  defects  known  as  (1)  Myopia,  (2)  Hypermetropia,  (3)  Astig- 
matism, (4)  Spherical  Aberration,  (5)  Chromatic  Aberration. 


Fig.  380. — Diagrams  showing— 1,  normal  (emmetropic)  eye  bringing  parallel  rays  exactly  to  a 
focus  on  the  retina:  2,  normal  eye  adapted  to  a  near-point;  without  accommodation  the  rays  would 
be  f ocussed  behind  the  retina,  but  by  increasing  the  curvature  of  the  anterior  surface  of  the  lens 
(shown  by  a  dotted  line)  the  rays  are  f ocussed  on  the  retina  (as  indicated  by  the  meeting  of  the  two 
dotted  hues);  3,  hypermetropic  eye;  in  this  case  the  axis  of  the  eye  is  shorter,  and  the  lens  flatter, 
than  normal;  parallel  rays  are  f ocussed  behind  the  retina;  4,  myopic  eye;  in  this  case  the  axis  of  the 
eye  is  abnormally  long,  and  the  lens  too  convex ;  parallel  rays  are  f ocussed  in  front  of  the  retina. 

The  normal  (emmetropic)  eye  is  so  adjusted  that  parallel  rays  are 
brought  exactly  to  a  focus  on  the  retina  without  any  effort  of  accommo- 
dation^ (1,  Fig.  380).    Hence  all  objects  except  near  ones  (practically  all 


212 


HAND-BOOK  OF  PHYSIOLOGY. 


objects  more  than  twenty  feet  off)  are  seen  without  any  effort  of  accom- 
modation: in  other  words,  the  far-point  of  the  normal  eye  is  at  an  infinite 
distance.  In  viewing  near  objects  we  are  conscious  of  an  effort  (the  con- 
traction of  the  ciliary  muscle)  by  which  the  anterior  surface  of  the  lens  is 
rendered  more  convex,  and  rays  which  would  otherwise  be  focussed  behind 
the  retina  are  converged  upon  the  retina  (see  dotted  lines,  2,  Fig.  dSO). 

1.  Myopia  (short-sight)  (4,  Fig.  380).— This  defect  is  due  to  an 
abnormal  elongation  of  the  eyeball.  The  eye  is  usually  larger  than 
normal,  and  is  always  longer  than  normal;  the  lens  is  also  probably  too 
convex.  The  retina  is  too  far  from  the  lens,  and  consequently  parallel 
rays  are  focussed  in  front  of  the  retina,  and,  crossing,  form  little  cir- 
cles on  the  retina;  thus  the  images  of  distant  objects  are  blurred  and 
indistinct.  The  eye  is,  as  it  were,  permanently  adjusted  for  a  near-point. 
Eays  from  a  point  near  the  eye  are  exactly  focussed  in  the  retina.  But 
those  which  issue  fi-om  any  object  beyond  a  certain  distance  ( far-point) 
cannot  be  distinctly  focussed.  This  defect  is  corrected  by  concave  glasses, 
which  cause  the  rays  entering  the  eye  to  diverge;  hence  they  do  not 
come  to  a  focus  so  soon.  Sucli  glasses  of  course  are  only  needed  to  give 
a  clear  vision  of  distant  objects.  For  near  objects,  except  in  extreme 
cases,  they  are  not  required. 

2.  Hypermetropia  (long-sight)  (3,  Fig.  380). — This  is  the  reverse 
defect.  The  eye  is  too  short  and  the  lens  too  flat.  Parallel  rays  are 
focussed  behind  the  retina:  an  effort  of  accommodation  is  required  to 
focus  even  parallel  rays  on  the  retina;  and  when  they  are  divergent,  as, 
in  viewing  a  near  object,  the  accommodation  is  insufficient  to  focus  them. 
Thus  in  well-marked  cases  distant  objects  require  an  effort  of  accommo- 
dation and  near  ones  a  very  powerful  effort.  Thus  the  ciliary  muscle 
is  constantly  acting.  This  defect  is  obviated  by  the  use  of  convex  glasses, 
which  render  the  pencils  of  light  more  convergent.  Such  glasses  are  of 
course  especially  needed  for  near  objects,  as  in  reading,  etc.  They  rest 
the  eye  by  relieving  the  ciliary  muscle  from  excessive  work. 

3.  Astigmatism. — This  defect,  which  was  first  discovered  by  Airy, 
is  due  to  a  greater  curvature  of  the  eye  in  one  meridian  than  in  others. 
The  eye  may  be  even  myopic  in  one  plane  and  hypermetropic  in  others. 
Thus  vertical  and  horizontal  lines  crossing  each  other  cannot  both  be 
focussed  at  once;  one  set  stand  out  clearly  and  the  others  are  blurred  and 
indistinct.  This  defect,  which  is  present  in  a  slight  degree  in  all  eyes, 
is  generally  seated  in  the  cornea,  but  occasionally  in  the  lens  as  well;  it 
may  be  corrected  by  the  use  of  cylindrical  glasses  {i.e.  curved  only  in 
one  direction). 

•i.  Spherical  Aberration. — The  rays  of  a  cone  of  light  from  an  ob- 
ject situated  at  the  side  of  the  field  of  vision  do  not  meet  all  in  the  same 
point,  owing  to  tlieir  unequal  refraction;  for  the  refraction  of  the  rays 
which  pass  through  the  circumference  of  a  lens  is  greater  than  that  of 


THE  SENSES. 


213 


those  traversing  its  central  portion.  This  defect  is  known  as  spherical 
aherration,  and  in  the  camera,  telescope,  microscope,  and  other  optical  in- 
struments, it  is  remedied  by  the  interposition  of  a  screen  with  a  circular 
aperture  in  the  path  of  the  rays  of  light,  cutting  off  all  the  marginal  rays 
and  only  allowing  the  passage  of  those  near  the  centre.  Such  correction  is 
effected  in  the  eye  by  the  iris,  which  forms  an  annular  diaphragm  to  cover 
the  circumference  of  the  lens,  and  to  prevent  the  rays  from  passing  through 
any  part  of  the  lens  but  its  centre  which  corresponds  to  the  pupil.  The 
posterior  surface  of  the  iris  is  coated  with  pigment,  to  prevent  the  passage 
of  rays  of  light  through  its  substance.  The  image  of  an  object  will  be 
most  defined  and  distinct  when  the  pupil  is  narrow,  the  object  at  the 
proper  distance  for  vision,and  the  light  abundant;  so  that,  while  a  suffi- 
cient number  of  rays  are  admitted,  the  narrowness  of  the  pupil  may  pre- 
vent the  production  of  indistinctness  of  the  image  by  spherical  aherra- 
tion.  But  even  the  image  formed  by  the  rays  passing  through  the  cir- 
cumference of  the  lens,  when  the  pupil  is  much  dilated,  as  in  the  dark, 
or  in  a  feeble  light,  may,  under  certain  circumstances,  be  well  defined. 

Distinctness  of  vision  is  further  secured  by  the  outer  surface  of  the 
retina  as  well  as  the  posterior  surface  of  the  iris  and  the  ciliary  processes, 
being  coated  with  black  pigment,  which  absorbs  any  rays  of  light  that 
may  be  reflected  within  the  eye,  and  prevents  their  being  thrown  again 
upon  the  retina  so  as  to  interfere  with  the  images  there  formed.  The 
pigment  of  the  retina  is  especially  important  in  this  respect;  for  with  the 
exception  of  its  outer  layer  the  retina  is  very  transparent,  and  if  the  sur- 
face behind  it  were  not  of  a  dark  color,  but  capable  of  reflecting  the 
light,  the  luminous  rays  which  had  already  acted  on  the  retina  would  be 
reflected  again  through  it,  and  would  fall  upon  other  parts  of  the  same 
membrane,  producing  both  dazzling  from  excessive  light,  and  indistinct- 
ness of  the  images. 

5.  Chromatic  Aberration. — In  the  passage  of  light  through  an 
ordinary  convex  lens,  decomposition  of  each  ray  into  its  elementary 
colored  parts  commonly  ensues,  and  a  colored  margin  appears  around  the 
image,  owing  to  the  unequal  refraction  which  the  elementary  colors  un- 
dergo. In  optical  instruments  this,  which  is  termed  chromatic  aberration, 
is  corrected  by  the  use  of  two  or  more  lenses,  differing  in  shape  and  density, 
the  second  of  which  continues  or  increases  the  refraction  of  the  rays  pro- 
duced by  the  first,  but  by  recombining  the  individual  parts  of  each  ray 
into  its  original  white  light,  corrects  any  chromatic  aberration  which  may 
have  resulted  from  the  first.  It  is  probable  that  the  unequal  refractive 
power  of  the  transparent  media  in  front  of  the  retina  may  be  the  means 
by  which  the  eye  is  enabled  to  guard  against  the  effect  of  chromatic  aber- 
ration. The  human  eye  is  achromatic,  however,  only  so  long  as  the 
image  is  received  at  its  focal  distance  upon  the  retina,  or  so  long  as  the 
eye  adapts  itself  to  the  different  distances  of  sight.    If  either  of  these 


214 


HAND-BOOK  OF  PHYSIOLOGY. 


conditions  be  interfered  with,  a  more  or  less  distinct  appearance  of  colors 
is  produced. 

•  An  ordinary  ray  of  white  light  in  passing  through  a  prism,  is  refracted, 
i.e.,  bent  out  of  its  course,  but  the  different  colored  rays  which  go  to 
make  up  white  light  are  refracted  in  different  degrees,  and  therefore 
appear  as  colored  bands  fading  off  into  each  other:  thus  a  colored  band 
known  as  the  "spectrum''  is  produced,  the  colors  of  which  are  arranged 
as  follows: — red,  orange,  yellow,  green,  blue,  indigo,  violet;  of  these  the 
red  ray  is  the  least  and  the  violet  the  most  refracted.  Hence,  as  Helm- 
holtz  has  shown,  a  small  white  object  cannot  be  accurately  focussed  on 
the  retina,  for  if  we  focus  for  the  red  rays,  the  violet  are  out  of  focus, 
and  vice  versa :  such  objects,  if  not  exactly  focussed,  are  often  seen  sur- 
rounded by  a  pale  yellowish  or  bluish  fringe. 

For  similar  reasons  a  red  surface  looks  nearer  than  a  blue  one  at  an 
equal  distance,  because,  the  red  rays  being  less  refrangible,  a  stronger 
effort  of  accommodation  is  necessary  to  focus  them,  and  the  eye  is  ad- 
justed as  if  for  a  nearer  object,  and  therefore  the  red  surface  appears 
nearer. 

From  the  insufficient  adjustment  of  the  image  of  a  small  white  object, 
it  appears  surrounded  by  a  sort  of  halo  or  fringe.  This  phenomenon  is 
termed  Irradiation.  It  is  from  this  reason  that  a  white  square  on  a 
black  ground  appears  larger  than  a  black  square  of  the  same  size  on  white 
ground. 

As  an  optical  instrument,  the  eye  I's  superior  to  the  camera  in  the  fol- 
lowing, among  many  other  particulars,  which  may  be  enumerated  in 
detail.  1.  The  correctness  of  images  even  in  a  large  field  of  view.  2. 
The  simplicity  and  efficiency  of  the  means  by  which  chromatic  aberra- 
tion is  avoided.  3.  The  perfect  efficiency  of  its  adaptation  to  different 
distances.  In  the  photographic  camera,  it  is  well  known  that  only  a  com- 
paratively small  object  can  be  accurately  focussed.  In  the  photograph 
of  a  large  object  near  at  liand,  the  upper  and  lower  limits  are  always  more 
or  less  hazy,  and  vertical  lines  aj)pear  curved.  This  is  due  to  tlie  fact 
that  the  image  produced  by  a  convex  lens  is  really  slightly  curved  and  can 
only  be  received  without  distortion  on  a  slightly  curved  concave  screen, 
hence  the  distortion  on  o^  flat  surface  of  ground  glass.  It  is  different  Avitli 
the  eye,  since  it  possesses  a  concave  background,  upon  which  the  field  of 
vision  is  depicted,  and  with  which  the  curved  form  of  the  image  coincides 
exactly.  Thus,  the  defect  of  the  camera  obscura  is  entirely  avoided; 
for  the  eye  is  able  to  embrace  a  large  field  of  vision,  the  margins  of  wliich 
are  depicted  distinctly  and  without  distortion.  If  the  retina  had  a,  plane 
surface  like  the  ground  glass  plate  in  a  camera,  it  must  necessarily  be  much 
larger  than  is  really  the  case  if  we  were  to  see  as  much;  moreover,  the 
central  portion  of  the  field  of  vision  alone  would  give  a  good  clear  picture. 
(Bernstein.) 

B.  Defective  Accommodation — Presbyopia. — Tliis  condition  is 
due  to  the  gradual  loss  of  the  power  of  accommodation  which  is  part  of 


THE  SENSES. 


215 


the  general  decay  of  old  age.  In  consequence  the  patient  would  be  obliged 
in  reading  to  hold  his  book  further  and  further  away  in  order  to  focus 
the  letters,  till  at  last  the  letters  are  held  too  far  for  distinct  vision.  The 
defect  is  remedied  by  weak  convex  glasses,  which  are  very  commonly 
worn  by  old  people.  It  is  due  chiefly  to  the  gradual  increase  in  density 
of  the  lens,  which  is  unable  to  SAvell  out  and  become  convex  when  near 
objects  are  looked  at,  and  also  to  a  weakening  of  the  ciliary  muscle,  and 
a  general  loss  of  elasticity  in  the  parts  concerned  in  the  mechanism. 

Visual  Sensations. 

Excitation  of  the  Retina. — Light  is  the  normal  agent  in  the  exci- 
tation of  the  retina,  the  only  layer  of  which  capable  of  reacting  to  the 
stimulus  being  the  rods  and  cones.  The  proofs  of  this  statement  may  be 
summed  up  thus: — 

(1.)  The  point  of  entrance  of  the  optic  nerve  into  the  retina,  where 
the  rods  and  cones  are  absent,  is  insensitive  to  light  and  is  called  the 
blind  spot.  The  phenomenon  itself  is  very  readily  demonstrated.  If  we 
direct  one  eye,  the  other  being  closed,  upon  a  point  at  such  a  distance 
to  the  side  of  any  object,  that  the  image  of  the  latter  must  fall  upon  the 
retina  at  the  point  of  entrance  of  the  optic  nerve,  this  image  is  l-ost  either 
instantaneously,  or  very  soon.  If,  for  example,  we  close  the  left  eye,  and 
direct  the  axis  of  the  right  eye  steadily  toward  the  circular  spot  here 

•  + 

represented,  while  the  page  is  held  at  a  distance  of  about  six  inches  from 
the  eye,  both  dot  and  cross  are  visible.  On  gradually  increasing  the 
distance  between  the  eye  and  the  object,  by  removing  the  book  farther 
and  farther  from  the  face,  and  still  keeping  the  right  eye  steadily  on  the 
dot,  it  will  be  found  that  suddenly  the  cross  disappears  from  view,  while 
on  removing  the  book  still  farther,  it  suddenly  comes  in  sight  again. 
The  cause  of  this  phenomenon  is  simply  that  the  portion  of  retina  which 
is  occupied  by  the  entrance  of  the  optic  nerve,  is  quite  blind;  and  there- 
fore that  when  it  alone  occupies  the  field  of  vision,  objects  cease  to  be 
visible.  (2.)  In  the  fovea  centralis  and  macula  lutea,  which  contain  rods 
and  cones  but  no  optic  nerve-fibres,  light  produces  the  greatest  effect. 
In  the  latter,  cones  occur  in  larger  numbers,  and  in  the  former  cones 
without  rods  are  found,  whereas  in  the  rest  of  the  retina  which  is  not 
so  sensitive  to  light,  there  are  fewer  cones  than  rods.  We  may  conclude, 
therefore,  that  cones  are  even  more  important  to  vision  than  rods.  (3.) 
If  a  small  lighted  candle  be  moved  to  and  fro  at  the  side  of  and  close  to 
one  eye  in  a  dark  room  while  the  eyes  look  steadily  forward  into  the  dark- 
ness, a  remarkable  branching  figure  {PurJcinJe's  figures)  is  seen  floating 


216 


HAND-BOOK  OF  PlIYSIOLOOY. 


before  the  eye,  consisting  of  dark  lines  on  a  reddish  ground.  As  the 
candle  moves,  the  figure  moves  in  the  opposite  direction,  and  from  its 
whole  appearance  there  can  be  no  doubt  that  it  is  a  reversed  picture  of 
the  retinal  vessels  projected  before  the  eye.  The  two  large  branching 
arteries  passing  up  and  down  from  the  optic  disc  are  clearly  visible  to- 
gether with  their  minutest  branches.  A  little  to  one  side  of  the  disc,  in 
a  part  free  from  vessels,  is  seen  the  yellow  spot  in  the  form  of  a  slight  de- 
pression. This  remarkable  appearance  is  doubtless  due  to  shadows  of 
the  retinal  vessels  cast  by  the  candle.  The  branches  of  these  vessels  are 
chiefly  distributed  in  the  nerve-fibre  and  ganglionic  layers;  and  since  the 
light  of  the  candle  falls  on  the  retinal  vessels  from  in  front,  the  shadow 
is  cast  behind  them,  and  hence  those  elements  of  the  retina  which  perceive 
the  shadows  must  also  lie  behind  the  vessels.  Here,  then,  we  have  a 
clear  proof  that  the  light-perceiving  elements  of  the  retina  are  not  the 
fibres  of  the  optic  nerve  forming  the  innermost  layer  of  the  retina,  but  the 
external  layers  of  the  retina,  almost  certainly  the  rods  and  cones,  which 
indeed  appear  to  be  the  special  terminations  of  the  optic  nerve-fibres. 

Duration  of  Visual  Sensations. — The  chiration  of  the  sensation 
produced  by  a  luminous  impression  on  the  retina  is  always  greater  than 
that  of  the  impression  .which  produces  it.  However  brief  the  luminous 
impression,  the  effect  on  the  retina  always  lasts  for  about  one- eighth  of  a 
second.  Thus,  supposing  an  object  in  motion,  say  a  horse,  to  be  revealed 
on  a  dark  night  by  a  flash  of  lightning.  The  object  would  be  seen  appar- 
ently for  an  eighth  of  a  second,  but  it  would  not  appear  in  motion; 
because,  although  the  image  remained  oh  the  retina  for  this  time,  it  was 
really  revealed  for  such  an  extremely  short  period  (a  flash  of  lightning 
being  almost  instantaneous)  that  no  appreciable  movement  on  the  part  of 
the  object  could  have  taken  place  in  the  period  during  which  it  was  re- 
vealed to  the  retina  of  the  observer.  And  the  same  fact  is  proved  in  a 
reverse  way.  The  spokes  of  a  rapidly  revolving  wheel  are  not  seen  as 
distinct  objects,  because  at  every  point  of  the  field  of  vision  over  which 
the  revolving  spokes  pass,  a  given  impression  has  not  faded  before  another 
comes  to  replace  it.  Thus  every  part  of  the  interior  of  the  wheel  appears 
occupied. 

The  duration  of  the  after-sensation,  produced  by  an  object,  is  greater 
in  a  direct  ratio  with  the  duration  of  the  impression  which  caused  it. 
Hence  the  image  of  a  bright  object,  as  of  the  panes  of  a  window  through 
which  the  light  is  shining,  may  be  perceived  in  the  retina  for  a  consider- 
able period,  if  we  have  previously  kept  our  eyes  fixed  for  some  time  on 
it.  But  the  image  in  this  case  is  negative.  If,  however,  after  shutting 
the  eyes  for  some  time,  we  open  them  and  look  at  an  object  for  an  instant, 
and  again  close  tliem,  the  after-image  \&  positive. 

Intensity  of  Visual  Sensations. — It  is  quite  evident  that  the  more 
luminous  a  body  the  mure  intense  is  the  sensation  it  produces.    But  the 


THE  SENSES. 


217 


intensity  of  the  sensation  is  not  directly  proportional  to  the  intensity  of 
the  himinosity  of  the  object.  It  is  necessary  for  light  to  have  a  certain 
intensity  before  it  can  excite  the  retina,  but  it  is  impossible  to  fix  an 
arbitrary  limit  to  the  power  of  excitability.  As  in  other  sensations,  so 
also  in  visual  sensations,  a  stimulus  may  be  too  feeble  to  produce  a  sen- 
sation. If  it  be  increased  in  amount  sufficiently  it  begins  to  produce  an 
effect  which  is  increased  on  the  increase  of  the  stimulation;  this  increase 
in  the  effect  is  not  directly  proportional  to  the  increase  in  the  excitation, 
but,  according  to  Feclmefs  laiv,  "as  the  logarithm  of  the  stimulus,"  i.e., 
in  each  sensation,  there  is  a  constant  ratio  between  the  increase  in  the 
stimulus  and  the  increase  in  the  sensation,  this  constant  ratio  for  each 
sensation  expresses  the  least  perceptible  increase  in  the  sensation  or  min- 
imal increment  of  excitation. 

This  law,  which  is  true  only  within  certain  limits,  may  be  best  under- 
stood by  an  example.  When  the  retina  has  been  stimulated  by  the  light 
of  one  candle,  the  light  of  two  candles  will  produce  a  difference  in  sensa- 
tion which  can  be  distinctly  felt.  If,  however,  the  first  stimulus  had 
been  that  of  an  electric  light,  the  addition  of  the  light  of  a  candle  would 
make  no  difference  in  the  sensation.  So,  generally,  for  an  additional 
stimulus  to  be  felt,  it  may  be  proportionately  small  if  the  original  stim- 
ulus have  been  small,  and  must  be  greater  if  the  original  stimulus  have 
been  great.  The  stimulus  increases  as  the  ordinary  numbers,  while  the 
sensation  increases  as  the  logarithm. 

The  Ophthalmoscope. — Part  of  the  light  which  enters  the  eye  is 
absorbed,  and  produces  some  change  in  the  retina,  of  which  we  shall  treat 
further  on;  the  rest  is  reflected. 

Every  one  is  perfectly  familiar  with  the  fact,  that  it  is  quite  impos- 
sible to  see  the  fundus  or  back  of  another  person^s  eye  by  simply  looking 
into  it.  The  interior  of  the  eye  forms  a  perfectly  black  background  to 
the  pupil.  The  same  remark  applies  to  an  ordinary  photographic  camera, 
and  may  be  illustrated  by  the  difficulty  we  experience  in  seeing  into  a 
room  from  the  street  through  the  window,  unless  the  room  be  lighted 
within.  In  the  case  of  the  eye  this  fact  is  partly  due  to  the  feebleness  of 
the  light  reflected  from  the  retina,  most  of  it  being  absorbed  by  the  cho- 
roid, as  mentioned  above;  but  far  more  to  the  fact  that  every  such  ray  is 
reflected  straight  back  to  the  source  of  light  {e.g.,  candle),  and  cannot, 
therefore,  be  seen  by  the  unaided  eye  without  intercepting  the  incident 
light  from  the  candle,  as  well  as  the  reflected  rays  from  the  retina.  This 
difficulty  has  been  surmounted  by  the  ingenious  device  of  Helmholtz, 
now  so  extensively  used,  termed  the  oplitlialmoscope.  As  at  present  used, 
it  consists  of  a  small  slightly  concave  mirror,  by  which  light  is  reflected 
from  a  candle  into  the  eye.  The  observer  looks  through  a  hole  in  the 
mirror,  and  can  thus  explore  the  illuminated  fundus;  the  entrance  of  the 
optic  nerve  and  the  retinal  vessels  being  plainly  visible. 


218 


HAND-BOOK  OF  PHYSIOLOGY. 


Visual  Purple. — The  method  by  which  a  ray  of  light  is  able  to  stim- 
ulate the  endings  of  the  optic  nerve  in  the  retina  in  such  a  manner  that 
a  visual  sensation  is  perceived  by  the  cerebrum  is  not  yet  understood.  It 
is  supposed  that  the  change  effected  by  the  agency  of  the  light  which 
falls  upon  the  retina  is  in  fact  a  chemical  alteration  in  the  protoplasm, 
and  that  this  change  stimulates  the  optic  nerve-endings.  The  discovery 
of  a  certain  temporary  reddish-purple  pigmentation  of  the  outer  limbs  of 
the  retinal  rods  in  certain  animals  {e.g.,  frogs)  which  have  been  killed 
in  the  dark,  forming  the  so-called  visual  purple,  appeared  likely  to  offer 
some  explanation  of  the  matter,  especially  as  it  was  also  found  that  the 
pigmentation  disappeared  when  the  animal  was  exposed  to  light,  and  re- 
appeared when  the  light  was  removed,  and  also  that  it  underwent  distinct 
changes  of  color  when  other  than  white  light  was  used.  The  visual 
purple  cannot  however  be  absolutely  essential  to  the  due  production  of 
visual  sensations,  as  it  is  absent  from  the  retinal  cones,  and  from  the 
macula  lutea  and  fovea  centralis  of  the  human  retina,  and  does  not  ap- 
pear to  exist  at  all  in  the  retinas  of  some  animals,  e.g.,  bat,  dove,  and 
hen,  which  are,  nevertheless,  possessed  of  good  vision. 

If  the  operation  be  performed  quickly  enough,  the  image  of  an  object 
may  be  fixed  in  the  pigment  on  the  retina  by  soaking  the  retina  of  an 
animal,  which  has  been  killed  in  the  dark,  in  alum  solution. 

Electrical  Currents. — According  to  the  careful  researches  of  Dewar 
and  McKendrick,  and  of  Holmgren,  it  appears  that  the  stimulus  of  light 
is  able  to  produce  a  variation  of  the  natural  electrical  current  of  the 
retina.  The  current  is  at  first  increased  and  then  diminished.  McKen- 
drick believes  that  this  is  the  electrical  expression  of  those  chemical 
changes  in  the  retina  of  which  we  have  already  spoken. 

Visual  PEiiCEPTioi^s  and  Judgments. 

Reversion  of  the  Image. — The  direction  given  to  the  rays  by  their 
refraction  is  regulated  by  that  of  the  central  ray,  or  axis  of  the  cone, 
toward  which  the  rays  are  bent.  The  image  of  any  point  of  an  object  is, 
therefore,  as  a  rule  (the  exceptions  to  which  need  not  here  be  stated),  always 
formed  in  aline  identical  with  the  axis  of  the  cone  of  light,  as  in  the  line 
of  B  a,  or  a  h  (Fig.  381),  so  that  the  spot  where  the  image  of  any  point 
will  be  formed  upon  the  retina  may  be  determined  by  prolonging  the 
central  ray  of  the  cone  of  light,  or  that  ray  which  traverses  the  centre  of 
the  pupil.  Thus  A  J  is  the  axis  or  central  ray  of  the  cone  of  light  issuing 
from  a;  B  «  the  central  ray  of  the  cone  of  liglit  issuing  from  b;  the 
image  of  A  is  formed  at  h,  the  image  of  b  at  a,  in  the  inverted  position; 
therefore  what  in  the  object  was  above  is  in  the  image  below,  and  vice 
versd, — the  right  hand  part  of  the  object  is  in  the  image  to  the  left,  the 


THE  SENSES. 


219 


left-hand  to  the  right.  If  an  opening  be  made  in  an  eye  at  its  superior 
surface,  so  that  the  retina  can  be  seen  through  the  vitreous  humor,  this 
reversed  image  of  any  bright  object,  such  as  the  windows  of  the  room, 
may  be  perceived  at  the  bottom  of  the  eye.  Or  stiil  better,  if  the  eye  of 
any  albino  animal,  such  as  a  white  rabbit,  in  which  the  coats,  from  the 
absence  of  pigment,  are  transparent,  is  dissected  clean,  and  held  with  the 
cornea  toward  the  window,  a  very  distinct  image  of  the  window  com- 
pletely inverted  is  seen  depicted  on  the  posterior  translucent  wall  of  the 


eye.  Volkmann  has  also  shown  that  a  similar  experiment  may  be  success- 
fully performed  in  a  living  person  possessed  of  large  prominent  eyes,  and 
an  unusually  transparent  sclerotic. 

An  image  formed  at  any  point  on  the  retina  is  referred  to  a  point  out- 
side the  eye,  lying  on  a  straight  line  drawn  from  the  point  on  the  retina 
outward  through  the  centre  of  the  pupil.  Thus  an  image  on  the  left  side 
of  the  retina  is  referred  by  the  mind  to  an  object  on  the  right  side  of  the 
eye,  and  vice  versa.  Thus  all  images  on  the  retina  are  mentally,  as  it 
were,  projected  in  front  of  the  eye,  and  the  objects  are  seen  erect  though 
the  image  on  the  retina  is  reversed.  Much  needless  confusion  and  diffi- 
culty have  been  raised  on  this  subject  for  want  of  remembering  that  when 
we  are  said  to  see  an  object,  the  mind  is  merely  conscious  of  the  picture 
on  the  retina,  and  when  it  refers  it  to  the  external  object,  or  ^'projects''* 
it  outside  the  eye,  it  necessarily  reverses  it  and  sees  the  object  as  erect, 
though  the  retinal  image  is  inverted.  This  is  further  corroborated  by 
the  sense  of  touch.  Thus  an  object  whose  picture  falls  on  the  left  half 
of  the  retina  is  reached  by  the  right  hand,  and  hence  is  said  to  lie  to  the 
right.  Or,  again,  an  object  whose  image  is  formed  on  the  upper  part 
of  the  retina  is  readily  touched  by  the  feet,  and  is  therefore  said  to  be 
in  the  lower  part  of  the  field,  and  so  on. 

Hence  it  is,  also,  that  no  discordance  arises  between  the  sensations  of 
inverted  vision  and  those  of  touch,  which  perceives  everything  in  its  erect 
position;  for  the  images  of  all  objects,  even  of  our  own  limbs,  in  the 
retina,  are  equally  inverted,  and  therefore  maintain  the  same  relative 
position. 

Even  the  image  of  our  hand,  while  used  in  touch,  is  seen  inverted. 
The  position  in  which  we  see  objects,  we  call,  therefore,  the  erect  posi- 


FiG.  381.— Diagram  of  the  formation  of  the  image  on  the  retina. 


220 


HAND-BOOK  OF  PHYSIOLOGY. 


tion.  A  mere  lateral  inversion  of  our  body  in  a  mirror,  where  tlie  right 
hand  occupies  the  left  of  the  image,  is  indeed  scarcely  remarked:  and 
there  is  but  little  discordance  between  the  sensations  acquired  by  touch 
in  regulating  our  movements  by  the  image  in  the  mirror,  and  those  of 
sight,  as,  for  example,  in  tying  a  knot  in  the  cravat.  There  is  some  want 
of  harmony  here,  on  account  of  the  inversion  being  only  lateral,  and  not 
complete  in  all  directions. 

The  perception  of  the  erect  position  of  objects  appears,  therefore,  to 
be  the  result  of  an  act  of  the  mind.  And  this  leads  us  to  a  consideration 
of  the  several  other  properties  of  the  retina,  and  of  the  co-operation  of 
the  mind  in  the  several  other  parts  of  the  act  of  vision.  To  these  belong 
not  merely  the  act  of  sensation  itself  and  the  perception  of  the  changes 
produced  in  the  retina,  as  light  and  colors,  but  also  the  conversion  of  the 
mere  images  depicted  in  the  retina  into  ideas  of  an  extendsd  field  of 
vision,  of  proximity  and  distance,  of  the  form  and  size  of  objects,  of  the 
reciprocal  influence  of  different  parts  of  the  retina  upon  each  other,  the 
simultaneous  action  of  the  two  eyes,  and  some  other  phenomena. 

Field  of  Vision. — The  actual  size  of  the  field  of  vision  depends  on 
the  extent  of  the  retina,  for  only  so  many  images  can  be  seen  at  any  one 
time  as  can  occupy  the  retina  at  the  same  time;  and  thus  considered,  the 
retina,  of  which  the  affections  are  perceived  by  the  mind,  is  itself  the 
field  of  vision.  But  to  the  mind  of  the  individual  the  size  of  the  field  of 
vision  has  no  determinate  limits;  sometimes  it  appears  very  small,  at 
another  time  very  large;  for  the  mind  has  the  power  of  projecting  images 
on  the  retina  toward  the  exterior.  Hence  the  mental  field  of  vision  is 
very  small  when  the  sphere  of  the  action  of  the  mind  is  limited  to  impedi- 
ments near  the  eye:  on  the  contrary,  it  is  very  extensive  when  the  pro- 
jection of  the  images  on  the  retina  toward  the  exterior,  by  the  influence 
of  the  mind,  is  not  impeded.  It  is  very  small  when  w^e  look  into  a 
hollow  body  of  small  capacity  held  before  the  eyes;  large  when  we  look 
out  upon  the  landscape  through  a  small  opening;  more  extensive  when 
we  look  at  the  landscape  through  a  wirdow;  and  most  so  when  our  view 
is  not  confined  by  any  near  object.  In  all  these  cases  the  idea  Avhich  we 
receive  of  the  size  of  the  field  of  vision  is  very  different,  although  its 
absolute  size  is  in  all  the  same,  being  dependent  on  the  extent  of  the 
retina.  Hence  it  follows,  that  the  mind  is  constantly  co-operating  in  the 
acts  of  vision,  so  that  at  last  it  becomes  difficult  to  say  what  belongs  to 
mere  sensation,  and  what  to  the  influence  of  the  mind.  By  a  mental 
operation  of  this  kind  we  obtain  a  correct  idea  of  the  size  of  individual 
objects,  as  well  as  of  tlie  extent  of  the  field  of  vision.  To  illustrate  this, 
it  will  be  well  to  refer  to  Fig.  382. 

The  angle  x,  included  between  the  decussating  central  rays  of  two 
cones  of  light  issuing  from  different  points  of  an  object,  is  called  the 
optical  angle — anguUis  opticus  seit  visorius.    This  angU>  becomes  larger. 


THE  SENSES. 


221 


the  greater  the  distance  between  the  points  A  and  b;  and  since  the  angles 
X  and  ?/  are  equal,  the  distance  between  the  points  a  and  h  in  the  image  on 
the  retina  increases  as  the  angle  becomes  larger.  Objects  at  different 
,  distances  from  the  eye,  but  having  the  same  optical  angle  x — for  example, 
the  objects  c,  d,  and  e, — must  also  throw  images  of  equal  size  upon  the 
retina;  and,  if  they  occupy  the  same  angle  of  the  field  of  vision,  their 
image  must  occupy  the  same  spot  in  the  retina. 

Nevertheless,  these  images  appear  to  the  mind  to  be  of  very  unequal 
size  when  the  ideas  of  distance  and  proximity  come  into  play;  for,  from 


Fig.  382.— Diagram  of  the  optical  angle. 


the  image  a  h,  the  mind  forms  the  conception  of  a  visual  space  extending 
to  e,  df  or  c,  and  of  an  object  of  the  size  which  that  represented  by  the 
image  on  the  retina  appears  to  have  when  viewed  close  to  the  eye,  or 
under  the  most  usual  circumstances. 

Estimation  of  Size. — Our  estimate  of  the  size  of  various  objects  is 
based  partly  on  the  visual  angle  under  which  they  are  seen,  but  much 
more  on  the  estimate  we  form  of  their  distance.  Thus  a  lofty  mountain 
many  miles  off  may  be  seen  under  the  same  visual  angle  as  a  small  hill 
near  at  hand,  but  we  infer  that  the  former  is  much  the  larger  object  be- 
cause we  know  it  is  much  further  off  than  the  hill.  Our  estimate  of  dis- 
tance is  often  erroneous,  and  consequently  the  estimate  of  size  also. 
Thus  persons  seen  walking  on  the  top  of  a  small  hill  against  a  clear  twi- 
light sky  appear  unusually  large,  because  we  over-estimate  their  distance, 
and  for  similar  reasons  most  objects  in  a  fog  appear  immensely  magnified. 
The  same  mental  process  gives  rise  to  the  idea  of  depth  in  the  field  of 
vision;  this  idea  being  fixed  in  our  mind  principally  by  the  circumstance 
that,  as  we  ourselves  move  forward,  different  images  in  succession  become 
depicted  on  our  retina,  so  that  we  seem  to  pass  between  these  images, 
which  to  the  mind  is  the  same  thing  as  passing  between  the  objects 
themselves. 

The  action  of  the  sense  of  vision  in  relation  to  external  objects  is, 
therefore,  quite  different  from  that  of  the  sense  of  touch.  The  objects 
of  the  latter  sense  are  immediately  present  to  it;  and  our  own  body,  with 
which  they  come  into  contact,  is  the  measure  of  their  size.  The  part  of 
a  table  touched  by  the  hand  appears  as  large  as  the  part  of  the  hand  re- 
ceiving an  impression  from  it,  for  a  part  of  our  body  in  which  a  sensation 
is  excited,  is  here  the  measure  by  which  we  judge  of  the  magnitude  of 


222 


HAND-BOOK  OF  PHYSIOLOGY. 


the  object.  In  the  sense  of  vision,  on  the  contraiy,  the  images  of  objects 
are  mere  fractions  of  the  objects  themselves  realized  upon  the  retina,  the 
extent  of  which  remains  constantly  the  same.  But  the  imagination,  which 
analyzes  the  sensations  of  vision,  invests  the  images  of  objects,  together 
with  the  whole  field  of  vision  in  the  retina,  with  very  varying  dimensions; 
the  relative  size  of  the  image  in  proportion  to  the  whole  field  of  vision, 
or  of  the  affected  parts  of  the  retina  to  the  whole  retina,  alone  remaining 
unaltered. 

Estimation  of  Direction. — The  direction  in  which  an  object  is  seen, 
depends  on  the  part  of  the  retina  which  receives  the  image,  and  on  the 
distance  of  this  part  from,  and  its  relation  to,  the  central  point  of  the 
retina.  Thus,  objects  of  which  the  images  fall  upon  the  same  parts  of 
the  retina  lie  in  the  same  visual  direction;  and  when,  by  the  action  of  the 
mind,  the  images  or  affections  of  the  retina  are  projected  into  the  exterior 
world,  the  relation  of  the  images  to  each  other  remains  the  same. 

Estimation  of  Form. — The  estimation  of  the  form  of  bodies  by 
sight  is  the  result  partly  of  the  mere  sensation,  and  partly  of  the  associ- 
ation of  ideas.  Since  the  form  of  the  images  perceived  by  the  retina 
depends  wholly  on  the  outline  of  the  part  of  the  retina  affected,  the  sen- 
sation alone  is  adequate  to  the  distinction  of  only  superficial  forms  of  each 
other,  as  of  a  square  from  a  circle.  But  the  idea  of  a  solid  body  as  a 
sphere,  or  a  body  of  three  or  more  dimensions,  e.g.,  a  cube,  can  only  be 
attained  by  the  action  of  the  mind  constructing  it  from  the  different 
superficial  images  seen  in  different  positions  of  the  eye  with  regard  to  the 
object,  and,  as  shown  by  Wheatstone  and  illustrated  in  the  stereoscope, 
from  two  different  perspective  projections  of  the  body  being  presented 
simultaneously  to  the  mind  by  the  two  eyes.  Hence,  when,  in  adult  age, 
sight  is  suddenly  restored  to  persons  blind  from  infancy,  all  objects  in  the 
field  of  vision  appear  at  first  as  if  painted  flat  on  one  surface;  and  no  idea 
of  solidity  is  formed  until  after  long  exercise  of  the  sense  of  vision  com- 
bined with  that  of  touch. 

The  clearness  with  which  an  object  is  perceived  irrespective  of  accom- 
modation, w^ould  appear  to  depend  largely  on  the  number  of  rods  and 
cones  which  its  retinal  image  covers.  Hence  the  nearer  an  object  is  to 
the  eye  (within  moderate  limits)  the  more  clearly  are  all  its  details  seen. 
Moreover,  if  we  want  carefully  to  examine  any  object,  we  always  direct 
the  eyes  straight  to  it,  so  tliat  its  image  shall  fall  on  the  yellow  spot  where 
an  image  of  a  given  area  will  cover  a  larger  number  of  cones  than  any- 
where else  in  the  retina.  It  has  been  found  that  the  images  of  two  points 
must  be  at  least  yTj-^oir  ^i^-  Jip^^i't  on  the  yellow  spot  in  order  to  be  dis- 
tinguished separately;  if  the  images  are  nearer  together,  the  points  appear 
as  one.    Tlie  diameter  of  each  one  in  this  part  of  the  retina  is  about 

TIT  0  0  0 

Estimation  of  Movement. — We  judge  of  the  motion  of  an  object, 


THE  SENSES. 


223 


partly  from  the  motion  of  its  image  over  the  surface  of  the  retina,  and 
partly  from  the  motion  of  our  eyes  following  it.  If  the  image  upon  the 
retina  moves  while  our  eyes  and  our  body  are  at  rest,  we  conclude  that 
the  object  is  changing  its  relative  position  with  regard  to  ourselves.  In 
such  a  case  the  movement  of  the  object  may  be  apparent  only,  as  when 
we  are  standing  upon  a  body  which  is  in  motion,  such  as  a  ship.  If,  on 
the  other  hand,  the  image  does  not  move  with  regard  to  the  retina,  but 
remains  fixed  upon  the  same  spot  of  that  membrane,  while  our  eyes  fol- 
low the  moving  body,  we  judge  of  the  motion  of  the  object  by  the  sen- 
sation of  the  muscles  in  action  to  move  the  eye.  If  the  image  moves 
over  the  surface  of  the  retina  while  the  muscles  of  the  eye  are  acting 
at  the  same  time  in  a  manner  corresponding  to  this  motion,  as  in  read- 
ing, we  infer  that  the  object  is  stationary,  and  we  know  that  we  are 
merely  altering  the  relations  of  our  eyes  to  the  object.  Sometimes  the 
object  appears  to  move  when  both  object  and  eye  are  fixed,  as  in  vertigo. 

The  mind  can,  by  the  faculty  of  attention, concentrsite  its  activity  more 
or  less  exclusively  upon  the  sense  of  sight,  hearing,  and  touch  alternately. 
When  exclusively  occupied  with  the  action  of  one  sense,  it  is  scarcely  con- 
scious of  the  sensations  of  the  others.  The  mind,  when  deeply  immersed 
in  contemplations  of  another  nature,  is  indifferent  to  the  actions  of  the 
sense  of  sight,  as  of  every  other  sense.  We  often,  when  deep  in  thought, 
have  our  eyes  open  and  fixed,  but  see  nothing,  because  of  the  stimulus 
of  ordinary  light  being  unable  to  excite  the  brain  to  perception,  when 
otherwise  engaged.  The  attention  which  is  thus  necessary  for  vision,  is 
necessary  also  to  analyze  what  the  field  of  vision  presents.  The  mind  does 
not  perceive  all  the  objects  presented  by  the  field  of  vision  at  the  same 
time  with  equal  acuteness,  but  directs  itself  first  to  one  and  then  to  an- 
other. The  sensation  becomes  more  intense,  according  as  the  particular 
object  is  at  the  time  the  principal  object  of  mental  contem- 
plation. Any  compound  mathematical  figure  produces  a 
different  impression  according  as  the  attention  is  directed 
exclusively  to  one  or  the  other  part  of  it.  Thus  in  Fig. 
383,  we  may  in  succession  have  a  vivid  perception  of  the 
whole,  or  of  distinct  parts  only;  of  the  six  triangles  near  the 
outer  circle,  of  the  hexagon  in  the  middle,  or  of  the  three 
large  triangles.  The  more  numerous  and  varied  the  j)arts  of  which  a 
figure  is  composed,  the  more  scope  does  it  afford  for  the  play  of  the  atten- 
tion. Hence  it  is  that  architectural  ornaments  have  an  enlivening  effect 
on  the  sense  of  vision,  since  they  afford  constantly  fresh  subject  for  the 
action  of  the  mind. 

Color  Sensations. — If  a  ray  of  sunlight  be  allowed  to  pass  through 
a  prism,  it  is  decomposed  by  its  passage  into  rays  of  different  colors,  which 
are  called  the  colors  of  the  spectrum;  they  are  red,  orange,  yellow,  green, 


224 


HAND-BOOK  OF  PHYSIOLOGY. 


blue,  indigo,  and  violet.  The  red  rays  are  the  least  turned  out  of  their 
course  by  the  prism,  and  the  violet  the  most,  whilst  the  other  colors  oc- 
cupy in  order  places  between  these  two  extremes.  The  differences  in  the 
color  of  the  rays,  depend  upon  the  number  of  vibrations  producing  each, 
the  red  rays  being  the  least  rapid  and  the  violet  the  most.  In  addition 
to  the  colored  rays  of  the  spectrum,  there  are  others  which  are  invisible, 
but  which  have  definite  properties,  those  to  the  left  of  the  red,  and  less 
refrangible,  being  the  calorific  rays  which  act  upon  the  thermometer,  and 
those  to  the  right  of  the  violet  which  are  called  the  actinic  or  chemical 
rays,  which  have  a  powerful  chemical  action.  The  rays  which  can  be 
perceived  by  the  brain  as  visual  rays,  i.e.,  the  colored  rays,  must  stimu- 
late the  retina  in  some  special  manner  in  order  that  colored  vision  may 
result,  and  two  chief  explanations  of  the  method  of  stimulation  have  been 
suggested.  The  one,  originated  by  Young  and  elaborated  by  Helmholtz, 
holds  that  there  are  three  primary  colors,  viz.,  red,  green,  and  violet,  and 
that  in  the  retina  are  contained  rods  or  cones  which  answer  to  each  of 
these  primary  colors,  whereas  the  innumerable  intermediate  shades  of  color 
are  produced  by  stimulation  of  the  three  primary  color  terminals  in  differ- 
ent degrees;  the  sensation  of  white  being  produced  when  the  three  elements 
are  equally  excited.  Thus  if  the  retina  be  stimulated  by  rays  of  certain 
wave  length,  at  the  red  end  of  the  spectrum,  the  terminals  of  the  other 
colors,  green  and  violet,  are  hardly  stimulated  at  all,  but  the  red  terminals 
being  strongly  stimulated,  the  resulting  sensation  is  red.  The  orange 
rays  excite  the  red  terminals  considerably,  the  green  rather  more,  and  the 
violet  slightly,  the  resulting  sensation  being  that  of  orange,  and  so  on. 

The  second  theory  of  color  (Hering's)  supposes  that  there  are  six 
primary  color  sensations,  of  three  pair  of  antagonistic  or  complemental 
colors,  black  and  white,  red  and  green,  and  yellow  and  blue,  and  that  these 
are  produced  by  the  changes  either  of  disintegration  or  of  assimilation 
taking  place  in  certain  substances,  somewhat  it  may  be  supposed  of  the 
nature  of  the  visual  purple,  which  (the  theory  supposes  to)  exist  in  the 
retina.  Each  of  the  substances  corresponding  to  a  pair  of  colors,  being 
capable  of  undergoing  two  changes,  one  of  construction  and  the  other  of 
disintegration,  with  the  result  of  producing  one  or  other  color.  For  in- 
stance, in  the  white-black  substance,  when  disintegration  is  in  excess  of 
construction  or  assimilation,  the  sensation  is  white,  and  when  assimilation 
is  in  excess  of  disintegration  the  reverse  is  the  case;  and  similarly  with 
the  rcd-gree]i  substance,  and  with  the  yellow-blue  substance.  AVhen  the 
repair  and  disintegration  are  equal  witli  the  first  substance,  the  visual 
sensation  is  grey;  but  in  the  other  pairs  when  this  is  the  case,  no  sensa- 
tion occurs.  Tlie  rays  of  the  spectrum  to  the  left  produce  changes  in  the 
red-green  substance  only,  with  a  resulting  sensation  of  red,  whilst  the 
(orange)  rays  further  to  the  right  affect  botli  the  red-green  and  the  yellow- 
blue  substances;  blue  rays  cause  constructive  changes  in  the  yellow-blue 


THE  SENSES. 


225 


substance,  but  none  in  the  red-green,  and  so  on.  These  changes  produced 
in  the  visual  substances  in  the  retina  are  perceived  by  the  brain  as  sensa- 
tions of  color. 

The  spectra  left  by  the  images  of  white  or  luminous  objects,  are  ordi- 
narily white  or  luminous;  those  left  by  dark  objects  are  dark.  Sometimes, 
however,  the  relation  of  the  light  and  dark  parts  in  the  image  may,  under 
certain  circumstances,  be  reversed  in  the  spectrum;  what  was  bright  may 
be  dark,  and  what  was  dark  may  appear  light.  This  occurs  whenever  the 
eye,  which  is  the  seat  of  the  spectrum  of  a  luminous  object,  is  not  closed, 
but  fixed  upon  another  bright  or  white  surface,  as  a  white  wall,  or  a  sheet 
of  white  paper.  Hence  the  spectrum  of  the  sun,  which,  while  light  is 
excluded  from  the  eye,  is  luminous,  appears  black  or  grey  when  the  eye  is 
directed  upon  a  white  surface.  The  explanation  of  this  is,  that  the  part 
of  the  retina  which  has  received  the  luminous  image  remains  for  a  certain 
period  afterward  in  an  exhausted  or  less  sensitive  state,  while  that  which 
has  received  a  dark  image  is  in  an  unexhausted,  and  therefore  much  more 
excitable  condition. 

The  ocular  spectra  which  remain  after  the  impression  of  colored  objects 
upon  the  retina  are  always  colored;  and  their  color  is  not  that  of  the  ob- 
ject, or  of  the  image  produced  directly  by  the  object,  but  the  opposite. 


Fig.  384.— Diagram  of  the  various  simple  and  compomid  colors  of  light,  and  those  which  are  com- 
plemental  of  each  other,  i.e.,  which,  when  mixed,  produce  a  neutral  grey  tint.  The  three  simple 
colors,  red,  yellow,  and  blue,  are  placed  at  the  angles  of  an  equilateral  triangle,  which  are  connected 
together  by  means  of  a  circle;  the  mixed  colors,  green,  orange,  and  violet,  are  placed  intermediate 
between  the  corresponding  simple  or  homogeneous  colors,  and  the  complemental  colors,  of  which 
the  pigments,  when  mixed,  would  constitute  a  grey,  and  of  which  the  prismatic  spectra  would  to- 
gether produce  a  white  light,  will  be  found  to  be  placed  in  each  case  opposite  to  each  other,  but  con- 
nected by  a  line  passing  through  the  centre  of  the  circle.  The  figure  is  also  useful  in  showing  the 
further  shades  of  color  which  are  complementary  of  each  other.  If  the  circle  be  supposed  to  contain 
every  transition  of  color  between  the  six  marked  down,  those  which,  when  united,  yield  a  white  or 
^ey  color,  will  always  be  found  directly  opposite  to  each  other;  thus,  for  example,  "the  intermediate 
tint  between  orange  and  red  is  complemental  of  the  middle  tint  between  green  and  blue. 


or  complemental  color.  The  spectrum  of  a  red  object  is,  therefore,  green; 
that  of  a  green  object,  red;  that  of  violet,  yellow;  that  of  yellow,  violet, 
and  so  on.  The  reason  of  this  is  obvious.  The  part  of  the  retina  which 
receives,  say,  a  red  image,  is  wearied  by  that  particular  color,  but  remains 
sensitive  to  the  other  rays  which  with  red  make  up  white  light;  and, 
therefore,  these  by  themselves  reflected  from  a  white  object  produce  a 
green  hue.  If,  on  the  other  hand,  the  first  object  looked  at  be  green, 
the  retina  being  tired  of  green  rays,  receives  a  red  image  when  the  eye  is 
Vol.  II.— 15. 


226 


HAT4i)-B()OK   OF  PHYSIOLOGY. 


turned  to  a  white  object.  And  so  witli  the  other  colors;  the  retina  while 
fatigued  by  yellow  rays  will  suppose  an  object  to  be  violet,  and  vice  versa; 
the  size  and  shape  of  the  spectrum  corresponding  with  the  size  and  shape 
of  the  original  object  looked  at.  The  colors  which  thjis  reciprocally  ex- 
cite each  other  in  the  retina  are  those  placed  at  opposite  points  of  the 
circle  in  Fig.  384.  The  peripheral  parts  of  the  retina  have  no  perception 
of  red.  The  area  of  the  retina  which  is  capable  of  receiving  impressions 
of  color  is  slightly  different  for  each  color. 

Color  Blindness  or  Daltonism. — Daltonism  or  color-blindness  is  a 
by  no  means  uncommon  visual  defect.  One  of  the  commonest  forms  is 
the  inability  to  distinguish  between  red  and  green.  The  simplest  ex- 
planation of  such  a  condition  is,  that  the  elements  of  the  retina  which 
receive  the  impression  of  red,  etc.,  are  absent,  or  very  imperfectly  devel- 
oped, or,  according  to  the  other  theory,  that  the  red-green  substance  is 
absent  from  the  retina.  Other  varieties  of  color  blindness  in  whicli  the 
other  color-perceiving  elements  are  absent  have  been  shown  to  exist 
occasionally. 

Of  the  Eecipkocal  Actions"  of  Differeitt  Paets  of  the  Eetii^a 

ox  each  other. 

Although  each  elementary  part  of  the  retina  represents  a  distinct  por- 
tion of  the  field  of  vision,  yet  the  different  elementary  parts,  or  sensitive 
points  of  that  membrane,  have  a  certain  influence  on  each  other;  the  par- 
ticular condition  of  one  influencing  that  of  another,  so  that  the  image 
perceived  by  one  part  is  modified  by  the  image  depicted  in  the  other. 
The  phenomena  which  result  from  this  relation  between  the  different 
parts  of  the  retina,  may  be  arranged  in  two  classes;  the  one  including 
those  where  the  condition  existing  in  the  greater  extent  of  the  retina  is 
imparted  to  the  remainder  of  that  membrane;  the  other,  consisting  of 
those  in  which  the  condition  of  the  larger  portion  of  the  retina  excites, 
in  the  less  extensive  portion,  the  opposite  condition. 

1.  When  two  opposite  impressions  occur  in  contiguous  parts  of  an 
image  on  the  retina,  the  one  impression  is,  under  certain  circumstances/ 
modified  by  the  other.  If  the  impressions  occupy  each  one-half  of  the 
image,  this  does  not  take  place;  for  in  that  case  their  actions  are  equally 
balanced.  But  if  one  of  the  impressions  occupies  only  a  small  part  of 
the  retina,  and  the  other  the  greater  part  of  its  surface,  the  latter  may, 
if  long  continued,  extend  its  influence  over  the  whole  retina,  so  that  the 
oi)posite  less  extensive  impression  is  no  longer  perceived,  and  its  place 
becomes  occupied  by  the  same  sensation  as  the  rest  of  the  field  of  vision. 
Thus,  if  we  fix  the  eye  for  some  time  upon  a  strip  of  colored  paper  lying 
upon  a  white  surface,  the  image  of  the  colored  object,  especially  when  it 


THE  SENSES. 


227 


falls  on  the  lateral  parts  of  the  retina,  will  gradually  disappear,  and  the 
white  surface  be  seen  in  its  place. 

2.  In  the  second  class  of  phenomena,  the  affection  of  one  part  of  the 
retina  influences  that  of  another  part,  not  in  such  a  manner  as  to  obliter- 
ate it,  but  so  as  to  cause  it  to  become  the  contrast  or  opposite  of  itself. 
Thus  a  grey  spot  upon  a  white  ground  appears  darker  than  the  same  tint 
of  grey  would  do  if  it  alone  occupied  the  whole  field  of  vision,  and  a 
shadow  is  always  rendered  deeper  when  the  light  which  gives  rise  to  it 
becomes  more  intense,  owing  to  the  greater  contrast. 

The  former  phenomena  ensue  gradually,  and  only  after  the  images 
have  been  long  fixed  on  the  retina;  the  latter  are  instantaneous  in  their 
production,  and  are  permanent. 

In  the  same  way,  also,  colors  may  be  produced  by  contrast.  Thus,  a 
very  small  dull  grey  strip  of  paper,  lying  upon  an  extensive  surface  of  any 


Fig.  385.— Diagram  of  the  axes  of  rotation  to  the  eye.  The  thin  lines  indicate  axes  of  rotation, 
the  thick  the  position  of  muscular  attachment.   (Modified  from  Fick.) 

bright  color,  does  not  appear  grey,  but  has  a  faint  tint  of  the  color  which 
is  the  complement  of  that  of  the  surrounding  surface.  A  strip  of  grey 
paper  upon  a  green  field,  for  example,  often  appears  to  have  a  tint  of  red, 
and  when  lying  upon  a  red  surface,  a  greenish  tint;  it  has  an  orange- 
colored  tint  upon  a  bright  blue  surface,  and  a  bluish  tint  upon  an  orange- 
colored  surface;  a  yellowish  color  upon  a  bright  violet,  and  a  violet  tint 
upon  a  bright  yellow  surface.  The  color  excited  thus,  as  a  contrast  to  the  ex- 
citing color,  being  wholly  independent  of  any  rays  of  the  corresponding 
color  acting  from  without  upon  the  retina,  must  arise  as  an  opposite  or 


228 


HAND-BOOK  OF  PHYSIOLOGY. 


antagonistic  condition  of  that  membrane;  and  the  opposite  conditions  of 
which  the  retina  thus  becomes  the  subject  would  seem  to  balance  each 
other  by  their  reciprocal  reaction.  A  oecessary  condition  for  the  pro- 
duction of  the  contrasted  colors  is,  tiiat  the  part  of  the  retina  in  which 
the  new  color  is  to  be  excited,  shall  be  in  a  state  of  comparative  repose; 
hence  the  small  object  itself  must  be  grey.  A  second  condition  is,  that 
the  color  of  the  surrounding  surface  shall  be  very  bright,  that  is,  it  shall 
contain  much  white  light. 

Movements  of  the  Eye. — The  eyeball  possesses  movement  around 
three  axes  indicated  in  Fig.  385,  viz.,  an  antero-posterior,  a  vertical,  and 
a  transverse,  passing  through  a  centre  of  rotation  a  little  behind  the 
centre  of  the  optic  axis.  The  movements  are  accomplished  by  pairs  of 
muscles. 


Moveme7its. 

Inward 
Outward 

Upward 
Downward  . 
Inward  and  upward 
Inward  and  downward 
Outward  and  upward 
Outward  and  downward 


Bi)  tvhat  muscles  accomplished. 

Internal  rectus. 

External  rectus, 
j  Superior  rectus. 
( Inferior  oblique. 

Inferior  rectus. 

Superior  oblique. 

Internal  and  superior  rectus. 

Inferior  oblique. 

Internal  and  inferior  rectus. 

Superior  oblique. 

External  and  superior  rectus. 

Inferior  oblique, 
j  External  and  inferior  rectus. 
(  Superior  oblique. 


Of  the  SiMULTAlTEOUS  ACTIOi^"  OF  THE  TwO  EyES. 

Although  the  sense  of  sight  is  exercised  by  two  organs,  yet  the  im- 
pression of  an  object  conveyed  to  the  mind  is  single.  Various  theories 
have  been  advanced  to  account  for  this  phenomenon.  By  Gall  it  was 
supposed  that  we  do  not  really  employ  both  eyes  simultaneously  in  vision, 
but  always  see  with  only  one  at  a  time.  This  especial  employment  of 
one  eye  in  vision  certainly  occurs  in  persons  whose  eyes  are  of  very  un- 
equal focal  distance,  but  in  the  majority  of  individuals  both  eyes  are  simul- 
taneously in  action,  in  the  perception  of  the  same  object;  this  is  shown 
by  the  double  images  seen  under  certain  conditions.  If  two  fingers  be  held 
up  before  the  eyes,  one  in  front  of  the  other,  and  vision  be  directed  to 
the  more  distant,  so  that  it  is  seen  singly,  the  nearer  will  appear  double; 
while,  if  the  nearer  one  be  regarded,  the  most  distant  will  be  seen  double; 
and  one  of  the  double  images  in  each  case  will  be  found  to  belong  to  one 
eye,  the  other  to  the  other  eye. 


THE  SENSES. 


229 


Diplopia. — Single  vision  results  only  when  certain  parts  of  the  two 
retinae  are  affected  simultaneously;  if  different  parts  of  the  retinae  receive 
the  image  of  the  object,  it  is  seen  double.  This  may  be  readily  illus- 
trated as  follows: — The  eyes  are  fixed  upon  some  near  object,  and  one  of 
them  is  pressed  by  the  thumb  so  as  to  be  turned  slightly  in  or  out;  two 
images  of  the  object  (Diplopia  or  Double  Vision)  are  at  once  perceived, 
just  as  is  frequently  the  case  in  persons  who  squint.  This  diplopia  is  due 
to  the  fact  that  the  images  of  the  object  do  not  fall  on  corresponding 
points  in  the  two  retinae. 

The  parts  of  the  retinae  in  the  two  eyes  which  thus  correspond  to  each 
other  in  the  property  of  referring  the  images  which  affect  them  simulta- 
neously to  the  same  spot  in  the  field  of  vision,  are,  in  man,  just  those 
parts  which  would  correspond  to  each  other,  if  one  retina  were  placed 


exactly  in  front  of,  and  over  the  other  (as  in  Fig.  386,  c).  Thus  the  outer 
lateral  portion  of  one  eye  corresponds  to,  or,  to  use  a  better  term,  is  iden- 
tical with,  the  inner  portion  of  the  otlier  eye;  or  a  of  the  eye  A  (Fig.  386), 
with  a'  of  the  eye  b.  The  upper  part  of  one  retina  is  also  identical  with 
the  upper  part  of  the  other;  and  the  lower  parts  of  the  two  eyes  are  iden- 
tical with  each  other. 

This  is  proved  by  a  simple  experiment.  Pressure  upon  any  part  of 
the  ball  of  the  eye,  so  as  to  affect  the  retina,  produces  a  luminous  circle, 
seen  at  the  opposite  side  of  the  field  of  vision  to  that  on  which  the  pressure 
is  made.  If,  now,  in  a  dark  room,  we  press  with  the  finger  at  the  upper 
part  of  one  eye,  and  at  the  lower  part  of  the  other,  two  luminous  circles 
are  seen,  one  above  the  other:  so,  also,  two  figures  are  seen  when  pres- 
sure is  made  simultaneously  on  the  two  outer  or  the  two  inner  sides 
of  both  eyes.  It  is  certain,  therefore,  that  neither  the  upper  part  of  one 
retina  and  the  lower  part  of  the  other  are  identical,  nor  the  outer  lateral 
parts  of  the  two  retinae,  ngr  their  inner  lateral  portions.    But  if  pressure 


Fig.  386, 


Fig.  387. 


230 


HAND-BOOK  OF  PHYSIOLOGY. 


be  made  with  the  fingers  upon  both  eyes  simultaneously  at  their  lower 
part,  one  luminous  ring  is  seen  at  the  middle  of  the  upper  part  of  the 
field  of  vision;  if  the  pressure  be  applied  to  the  upper  part  of  both 
eyes  a  single  luminous  circle  is  seen  in  the  middle  of  the  field  of  vision 
below.  So,  also,  if  w^e  press  upon  the  outer  side  a  of  the  eye  A,  and  upon 
the  inner  side  a'  of  the  eye  b,  a  single  spectrum  is  produced,  and  is  appar- 
ent at  the  extreme  right  of  the  field  of  vision;  if  upon  the  point  I  of  one 
eye,  and  the  point  V  of  the  other,  a  single  spectrum  is  seen  to  the  extreme 
left. 

The  spheres  of  the  two  retinae  may,  therefore,  be  regarded  as  lying 
one  over  the  other,  as  in  c,  Fig.  386;  so  that  the  left  portion  of  one  eye 
lies  over  the  identical  left  portion  of  the  other  eye,  the  right  portion  of 
one  eye  over  the  identical  right  portion  of  the  other  eye;  and  with  the  upper 


Fig.  388. 


and  lower  portions  of  the  two  eyes,  a  lies  over  a' ,  h  over  h',  and  c  over  c'. 
The  points  of  the  one  retina  intermediate  between  a  and  c  are  again  identi- 
cal with  the  corresponding  points  of  the  other  retina  between  a'  and-  c'; 
those  between  I  and  c  of  the  one  retina,  with  those  between  and  c'  of 
the  other.  If  the  axes  of  the  eyes,  a  and  b  (Fig.  388),  be  so  directed 
that  they  meet  at  a,  an  object  at  a  will  be  seen  singly,  for  the  point  a  of 
the  one  retina,  and  a'  of  the  other,  are  identical.  So,  also,  if  the  object 
13  be  so  situated  that  its  image  falls  in  both  eyes  at  the  same  distance 
from  the  central  point  of  the  retina, — namely,  at  h  in  the  one  eye,  and 
at  Z>'  in  the  other, — f3  will  be  seen  single,  for  it  affects  identical  parts  of 
the  two  retinae.    The  same  Avill  apply  to  the  object  y. 

In  quadrupeds,  the  relation  between  the  identical  and  non-identical 
parts  of  the  retina  cannot  be  the  same  as  in  man;  for  the  axes  of  their 
eyes  generally  diverge,  and  can  never  be  made  to  meet  in  one  point  of 
an  object.    When  an  animal  regards  an  object  situated  directly  in  front  of 


THE  SENSES. 


231 


it,  the  image  of  the  object  must  fall,  in  both  eyes,  on  the  outer  portion 
of  the  retina.  Thus,  the  image  of  the  object  a  (Fig.  389)  will  fall  at  a' 
in  one,  and  at  a"  in  the  other:  and  these  points  a'  and  a"  must  be  iden- 
tical. So,  also,  for  distinct  and  single  vision  of  objects, 
I  or  G,  the  points  ^'and  h"  or  c'  in  the  two  retinae,  on  / 
which  the  images  of  these  objects  fall,  must  be  identi-  \  \ 
cal.  All  points  of  the  retina  in  each  eye  which  receive 
rays  of  light  from  lateral  objects  only,  can  have  no 
corresponding  identical  points  in  the  retina  of  the  other 
eye;  for  otherwise  two  objects,  pne  situated  to  the  right 
and  the  other  to  the  left,  would  appear  to  lie  in  the  same 
spot  of  the  field  of  vision.  It  is  probable,  therefore,  that 
there  are  in  the  eyes  of  animals,  parts  of  the  retinae  which  are  identical, 
and  parts  which  are  not  identical,  i.e.,  parts  in  one  which  have  no  cor- 
responding parts  in  the  other  eye.  And  the  relation  of  the  two  retinaa 
to  each  other  in  the  field  of  vision  may  be  represented  as  in  Fig.  389. 

Binocular  Vision. — The  cause  of  the  impressions  on  the  identical 
points  of  the  two  retinae  giving  rise  to  but  one  sensation,  and  the  percep- 
tion of  a  single  image,  must  either  lie  in  the  structural  organization  of  the 
deeper  or  cerebral  portion  of  the  visual  apparatus,  or  be  the  result  of  a 
mental  operation;  for  in  no  other  case  is  it  tha  property  of  the  corre- 
sponding nerves  of  the  two  sides  of  the  body  to  refer  their  sensations  as 
one  to  one  spot. 

Many  attempts  have  been  made  to  explain  this  remarkable  relation 
between  the  eyes,  by  referring  it  to  anatomical  relation  between  the  optic 
nerves.  The  circumstance  of  the  inner  portion  of  the  fibres  of  the  two 
optic  nerves  decussating  at  the  commissure  and  passing  to  the  eye  of  the 
opposite  side,  while  the  outer  portion  of  the  fibres  continue  their  course 
to  the  eye  of  the  same  side,  so  that  the  left  side  of  both  retinae  is  formed 
from  one  root  of  the  nerves,  and  the  right  side  of  both  retinae  from  the 
outer  root,  naturally  led  to  an  attempt  to  explain  the  phenomenon  by 
this  distribution  of  the  fibres  of  the  nerves.  And  this  explanation  is 
favored  by  cases  in  which  the  entire  of  one  side  of  the  retina,  as  far  as 
the  central  point  in  both  eyes,  sometimes  becomes  insensible.  But 
Miiller  shows  the  inadequateness  of  this  theory  to  explain  the  phenome- 
non, unless  it  be  supposed  that  each  fibre  in  each  cerebral  portion  of  the 
optic  nerves  divides  in  the  optic  commissure  into  two  branches  for  the 
identical  points  of  the  two  retinae,  as  is  shown  in  A,  Fig.  390.  But  there 
is  no  foundation  for  such  supposition. 

By  another  theory  it  is  assumed  that  each  optic  nerve  contains  exactly 
the  same  number  of  fibres  as  the  other,  and  that  the  corresponding  fibres 
of  the  two  nerves  are  united  in  the  Sensorium  (as  in  Fig.  390,  B).  But 
in  this  theory  no  account  is  taken  of  the  partial  decussation  of  the  fibres 
of  the  nerves  in  the  optic  commissure. 

According  to  a  third  theory,  the  fibres  a  and  a' ,  Fig.  390,  0,  coming 
from  identical  points  of  the  two  retinas,  are  in  the  optic  commissure 


232 


HAND-BOOK  OF  PHYSIOLOGY. 


brought  into  one  optic  nerve,  and  in  the  brain  either  are  united  by  a  loop 
or  spring  from  the  same  point.  The  same  disposition  prevails  in  the  case 
of  the  identical  fibres  h  and  h'.  According  to  this  theory  the  left  half 
of  each  retina  would  be  represented  in  the  left  hemisphere  of  the  brain, 
and  the  right  half  of  each  retina  in  the  right  hemisphere. 

Another  explanation  is  founded  on  the  fact,  that  at  the  anterior  part 
of  the  commissure  of  the  optic  nerve,  certain  fibres  pass  across  from  the 


ABC 


Fig.  390. 


distal  portion  of  one  nerve  to  the  corresponding  portion  of  the  other 
nerves,  as  if  they  were  commissural  fibres  forming  a  connection  between 
the  retinae  of  the  two  eyes.  It  is  supposed,  indeed,  that  these  fibres  may 
connect  the  corresponding  parts  of  the  two  retinse,  and  may  thus  explain 
their  unity  of  action;  in  the  same  way  that  corresponding  parts  of  the 
cerebral  hemispheres  are  believed  to  be  connected  together  by  the  com- 
missural fibres  of  the  corpus  callosum,  and  so  enabled  to  exercise  unity  of 
function. 

Judgment  of  Solidity. — On  the  whole,  it  is  probable,  that  the  power 
of  forming  a  single  idea  of  an  object  from  a  double  impression  conveyed  by 
it  to  the  eyes  is  the  result  of  a  mental  act.  This  view  is  supported  by  the 
same  facts  as  those  employed  by  Wheatstone  to  show  that  this  power  is 
subservient  to  the  purpose  of  obtaining  a  right  perception  of  bodies  raised 
in  relief.  "When  an  object  is  placed  so  near  the  eyes  that  to  view  it  the  optic 
axes  must  converge,  a  different  perspective  projection  of  it  is  seen  by  each 
eye,  these  perspectives  being  more  dissimilar  as  the  convergence  of  the  optic 
axes  becomes  greater.  Thus,  if  any  figure  of  three  dimensions,  an  out- 
line cube,  for  example,  be  held  at  a  moderate  distance  before  the  eyes, 
and  viewed  with  each  eye  successively  while  the  head  is  kept  perfectly 
steady,  a  (Fig.  391)  will  be  the  picture  presented  to  the  right  eye,  and 
B  that  seen  by  the  left  eye.  Wheatstone  has  shown  that  on  this  circum- 
stance depends  in  a  great  measure  our  conviction  of  the  solidity  of  an 
object,  or  of  its  projection  in  relief.  If  different  perspective  drawings 
of  a  solid  body,  one  representing  the  image  seen  by  the  right  eye,  the 
other  that  seen  by  the  left  (fur  example,  the  drawing  of  a  cube,  A,  u. 


THE  SENSES. 


233 


Fig.  391),  be  presented  to  corresponding  parts  of  the  two  retinae,  as  may 
be  readily  done  by  means  of  the  stereoscope,  the  mind  will  perceive  not 
merely  a  single  representation  of  the  object,  but  a  body  projecting  in 
relief,  the  exact  counterpart  of  that  from  which  the  drawings  were  made. 


Fig.  391. 


By  transposing  two  stereoscopic  pictures  a  reverse  effect  is  produced: 
the  elevated  parts  appear  to  be  depressed,  and  vice  versa.  An  instru- 
ment contrived  with  this  purpose  is  termed  a  pseudoscope.  Viewed  with 
this  instrument  a  bust  appears  as  a  hollow  mask,  and  as  may  readily  be 
imagined  the  effect  is  most  bewildering. 


CHAPTER  XX. 


GENEKATION  AND  DEVELOPMENT. 


The  several  organs  and  functions  of  the  human  body  which  have  been 
considered  in  the  previous  chapters,  have  relation  to  the  individual  be- 
ing. We  have  now  to  consider  those  organs  and  functions,  which  are  des- 
tined for  the  propagation  of  the  species.  These  comprise  the  several  pro- 
visions made  for  the  formation,  impregnation,  and  development  of  the 
ovum,  from  which  the  embryo  or  foetus  is  produced  and  gradually  per- 
fected into  a  fully-formed  human  being. 

The  organs  in  the  two  sexes  concerned  in  effecting  these  objects  are 
named  the  Generative  organs,  or  Sexual  apparatus. 


The  female  organs  of  generation  (Fig.  392)  consist  of  two  Ovaries, 
whose  function  is  the  formation  of  ova;  of  a  Fallopian  tube,  or  oviduct. 


Fig.  392.— Diagrammatic  view  of  the  uterus  and  its  appendages,  as  seen  from  behind.  The  uterus 
and  upper  part  of  the  vagina  have  been  laid  open  by  removing  tlie  posterior  wall;  the  Fallopian  tube, 
round  ligament,  and  ovarian  ligament  have  been  cut  short,  and  the  broad  ligament  removed  on  the 
leftside;  n,  the  upper  part  of  the  uterus;  r.  the  cervix  opposite  the  os  iutennuu;  the  triangular 
shape  of  the  uterine  cavity  is  shown,  and  the  (lilatatioii  of  the  cervical  cavity  with  the  ruga^  termed 
arbor  vita^;  v,  upper  part  of  the  vagina;  orf.  Fallopian  tube  or  oviduct;  the  narrow  conunuuication 
of  its  cavity  with  that  of  the  cornu  of  the  uterus  on  each  side  is  seen;  /,  round  ligament:  /o,  ligament 
of  the  ovary;  o,  ovary;  /,  wide  outer  part  of  the  right  Fallopian  tube;  ./(,  its  tlnibriatcd  extr(>mity; 
»o,  parovarium;  /i,  one  of  the  hydatids  frequently  found  connected  with  the  broad  ligament  .  }4- 
(Allen  Thomson.) 


(ionnected  with  each  ovary,  for  the  purpose  of  conducting  the  ovum  from 
the  ovary  to  the  Uterus,  or  ciivity  in  which,  if  im])rcgnatefl,  it  is  retained 
until  tlic  embryo  is  fully  developed,  and  fitted  to  maintain  its  existence  in- 


Geneeative  Organs  of  the  Female. 


GENERATION  AND  DEVELOPMENT. 


235 


dependently  r)i  internal  connection  with  the  parent;  and,  lastly,  of  a  canal, 
or  Vagina,  with  its  appendages,  for  the  reception  of  the  male  generative 
organs  in  the  act  of  copulation,  and  for  the  subsequent  discharge  of  the 
foetus. 

Ovaries. —The  ovaries  are  two  oval  compressed  bodies,  situated  in 
the  cavity  of  the  pelvis,  one  on  each  side,  enclosed  in  the  folds  of  the 
broad  ligament.  Each  ovary  measures  about  an  inch  and  a  half  in  length, 
three-quarters  of  an  inch  in  width,  and  nearly  half  an  inch  in  thickness. 


Fig.  393.— View  of  a  section  of  the  prepared  ovary  of  the  cat.  1,  outer  covering  and  free  border 
of  the  ovary;  1',  attached  border;  2.  the  ovarian  stroma,  presenting  a  fibrous  and  vascular  struc- 
ture; 3,  granular  substance  lying  external  to  the  fibrous  stroma;  4,  blood-vessels;  5,  ovigerms  in 
their  earliest  stages  occupying  a  part  of  the  granular  layer  near  the  surface;  6,  ovigerms  which  have 
begun  to  enlarge  and  to  pass  more  deeply  into  the  ovary;  7,  ovigerms  round  which  the  Graafian 
follicle  and  tunica  granulosa  are  now  formed,  and  which  have  passed  somewhat  deeper  into  the 
ovary  and  are  surrounded  by  the  fibrous  stroma;  8,  more  ad's^anced  Graafian  follicle  with  the  ovxmi 
imbedded  in  the  layer  of  cells  constituting  the  prohgerous  disc;  9,  the  most  advanced  follicle  con- 
taining the  ovum,  etc. ;  9',  a  follicle  from  which  the  ovum  has  accidentally  escaped ;  10,  corpus  luteimi, 
6-1.  (Schron.) 

and  is  attached  to  the  uterus  by  a  narrow  fibrous  cord  (the  ligament  of 
the  ovary),  and,  more  slightly,  to  the  Fallopian  tubes  by  one  of  the  fim- 
briae into  which  the  walls  of  the  extremity  of  the  tube  expand. 

Structure. — The  ovary  is  developed  by  a  capsule  of  dense  fibro-cellu- 
lar  tissue,  covered  on  the  outside  by  epithelium  (germ-epithelium),  the 
cells  of  which,  although  continuous  with,  and  originally  derived  from, 
the  squamous  epithelium  of  the  peritoneum,  are  short  columnar. 

The  term  germ-epitJielium  is  used  on  account  of  the  relation  which  it 
bears  in  early  life  to  the  development  of  the  ova;  the  ova  being  formed 
by  certain  of  these  epithelial  cells,  which,  becoming  modified  in  structure, 
are  gradually  enclosed  in  the  ovarian  stroma.   ( Waldeyer. )    (See  Fig.  394. ) 

The  internal  structure  of  the  organ  consists  of  a  peculiar  soft  fibrous 
tissue,  or  stroma,  abundantly  supplied  with  blood-vessels,  and  having 
embedded  in  it,  in  various  stages  of  development,  numerous  minute  fol- 
licles or  vesicles,  the  Graafian  vesicles',  or  sacculi,  containing  the  ova 
(Fig.  394). 


236 


HAND-BOOK  OF  PHYSIOLOGY. 


Graafian  Vesicles. — If  the  human  ovary  be  examined  at  any  period 
between  early  infancy  and  advanced  age,  but  especially  during  that  period 
of  life  in  which  the  power  of  conception  exists,  it  will  be  found  to  con- 
tain a  number  of  small  vesicles  or  membranous  sacs  of  various  sizes;  these 
have  been  already  alluded  to  as  the  follicles  or  vesicles  of  De  Oraaf,  the 
anatomist  who  first  accurately  described  them;  they  are  sometimes  called 
ovisacs. 

At  their  first  formation,  the  Graafian  vesicles  are  near  the  surface  of 
the  stroma  of  the  ovary,  but  subsequently  become  more  deeply  placed; 
and,  again,  as  they  increase  in  size,  make  their  way  toward  the  surface 
(Fig.  394). 

When  mature,  they  form  little  prominences  on  the  exterior  of  the  ovary, 
covered  only  by  a  thin  layer  of  condensed  fibrous  tissue  and  epithelium. 


Fig.  394. — Section  of  the  ovary  of  a  cat.  A,  germinal  epithelium;  B,  immature  Graafian  follicle; 
C,  stroma  of  ovary;  D,  vitelhne  membrane  containing  the  o^-um;  E,  Graafian  follicle  showing  lining 
cells;  F,  follicle  from  which  the  ovum  has  fallen  out.   (.V.  D.  Harris.) 

Each  follicle  has  an  external  membranous  envelope,  comprised  of  fine 
fibrous  tissue,  and  connected  with  the  surrounding  stroma  of  the  ovary  by 
networks  of  blood-vessels.  This  envelope  or  tunic  is  lined  with  a  layer  of 
nucleated  cells,  forming  a  kind  of  e2:)ithelium  or  internal  tunic,  and 
named  memhrana  granulosa.  The  cavity  of  the  follicle  is  filled  with  an 
albuminous  fluid  in  which  microscopic  granules  float;  and  it  contains  also 
the  ovum. 

Ovum. — The  ovum  is  a  minute  spherical  body  situated,  in  immature 
follicles,  near  the  centre;  but  in  those  nearer  matunty,  in  contact  with 
the  membrana  granulosa  at  that  part  of  the  follicle  which  forms  a  promi- 
nence on  the  surface  of  the  ovary.  The  cells  of  the  membrana-granuloso 
are  at  that  point  more  numerous  tlian  elsewhere,  and  are  heaped  around  the 
ovum,  forming  a  kind  of  granular  zone,  the  discus  proligcrus  (Fig.  395). 


GENERATION  AND  DEVELOPMENT. 


237 


In  order  to  examine  an  ovum,  one  of  the  Graafian  vesicles,  it  matters 
not  whether  it  be  of  small  size  or  arrived  at  maturity,  should  be  pricked, 
and  the  contained  fluid  received  upon  a  slide.  The  ovum  then,  being 
found  in  the  midst  of  the  fluid  by  means  of  a  simple  lens,  may  be  further 
examined  with  higher  microscopic  powers.  Owing  to  its  globular  form, 
however,  its  structure  cannot  be  seen  until  it  is  subjected  to  gentle  pressure. 

The  human  ovum  measures  about  yj-^j-  of  an  inch.  Its  external  invest- 
ment is  a  transparent  membrane,  about  ytow  i^^h  in  thickness,  which 
under  the  microscope  appears  as  a  bright  ring  (4,  Fig. 
395),  bounded  externally  and  internally  by  a  dark  out- 
line; it  is  called  the  zona  pellucida,  or  vitelline  mem- 
brane. It  adheres  externally  to  the  heap  of  cells  con- 
stituting the  discus  proligerus.  Within  this  transpar- 
ent investment  or  zona  pellucida,  and  usually  in  close 
contact  with  it,  lies  the  yolk  or  vitellus  which  is 
composed  of  granules  and  globules  of  various  sizes,  Fig.  395.— Ovumof  the 
imbedded  in  a  mpre  or  less  fluid  substance.  The  i^'geriillf'^e'Sdir^^^ 
smaller  granules,  which  are  the  more  numerous,  re-  5°Ssctis^p?Sii|l?lJ^i^i 
semble  in  their  appearance,  as  well  as  their  constant  ceDs.^^(Barfy.)^^^^  °^ 
motion,  pigment-granules.  The  larger  granules  or 
globules,  which  have  the  aspect  of  fat-globules,  are  in  greatest  number 
at  the  periphery  of  the  yolk.  The  number  of  the  granules  is,  according 
to  Bischoff,  greatest  in  the  ova  of  carnivorous  animals.  In  the  human 
ovum  their  quantity  is  comparatively  small. 

In  the  substance  of  the  yolk  is  imbedded  the  germinal  vesicle,  or  vesi- 
cula  germinativa  (2,  Tig.  395).  This  vesicle  is  of  greatest  relative  size  in 
the  smallest  ova,  and  is  in  them  surrounded  closely  by  the  yolk,  nearly 
,  in  the  centre  of  which  it  lies.  During  the  development  of  the  ovum,  the 
germinal  vesicle  increases  in  size  much  less  rapidly  than  the  yolk,  and 
comes  to  be  placed  near  to  its  surface.  It  is  about  of  an  inch  in 
diameter.  It  consists  of  a  fine,  transparent,  structureless  membrane, 
containing  a  clear,  watery  fluid,  in  which  are  sometimes  a  few  granules; 
and  at  that  part  of  the  periphery  of  the  germinal  vesicle  which  is 
nearest  to  the  periphery  of  the  yolk  is  situated  the  germinal  spot  (macula 
germinativa),  a  finely  granulated  substance,  of  a  yellowish  color,  strongly 
refracting  the  rays  of  light,  and  measuring  about  3-0V0  moh.  in 

diameter. 

Such  are  the  parts  of  which  the  Graafian  follicle  and  its  contents,  in- 
cluding the  ovum,  are  composed.  With  regard  to  the  mode  and  order  of 
development  of  these  parts  there  is  considerable  uncertainty;  but  it 
seems  most  likely  that  the  ovum  is  formed  before  the  Graafian  vesicle  or 
ovisac. 

With  regard  to  the  parts  of  the  ovum  first  formed,  it  appears  certain 
that  the  formation  of  the  germinal  vesicle  precedes  that  of  the  yolk  and 


238 


HAND-BOOK  OF  PHYSIOLOGY. 


zona  pellucida,  or  vitelline  membrane.  "Whether  the  germinal  spot  is 
formed  first,  and  the  germinal  vesicle  afterward  developed  around  it,  can- 
not be  decided  in  the  case  of  vertebrate  animals;  but  the  observations 
of  Kolliker  and  Bagge  on  the  development  of  the  ova  of  intestinal  worms 
show  that  in  these  animals,  the  first  step  in  the  process  is  the  production 
of  round  bodies  resembling  the  germinal  spots  of  ova,  the  germinal 
vesicles  being  subsequently  developed  around  these  in  the  form  of  trans- 
parent membranous  cells. 

From  the  earliest  infancy,  and  through  the  whole  fruitful  period  of 
life,  there  appears  to  be  a  constant  formation,  development,  and  matura- 
tion of  Graafian  vesicles,  with  their  contained  ova.  Until  the  period  of 
puberty,  however,  the  process  is  comparatively  inactive;  for,  previous  to 
this  period,  the  ovaries  are  small  and  pale,  the  Graafian  vesicles  in  them 
are  very  minute^  and  probably  never  attain  full  development,  but  soon 
shrivel  and  disappear,  instead  of  bursting,  as  matured  follicles  do;  the 
contained  ova  are  also  incapable  of  being  impregnated.  But,  coincident 
with  the  other  changes  which  occur  in  the  body  at  the  time  of  puberty, 
the  ovaries  enlarge,  and  become  very  vascular,  the  formation  of  Graafian 
vesicles  is  more  abundant,  the  size  and  degree  of  development  attained  by 
them  are  greater,  and  the  ova  are  capable  of  being  fecundated. 

Fallopian  Tubes. — The  Fallopian  tubes  are  about  four  inches  in 
length,  and  extend  between  the  ovaries  and  the  upper  angles  of  the 
uterus.  At  the  point  of  attachment  to  the  uterus,  the  Fallopian  tube  is 
very  narrow;  but  in  its  course  to  the  ovary  it  increases  to  about  a  line 
and  a  half  in  thickness;  at  its  distal  extremity,  which  is  free  and  floating, 
it  bears  a  number  of  fimlrice,  one  of  which,  longer  than  the  rest,  is 
attached  to  the  ovary.  The  canal  by  which  each  Fallopian  tube  is 
traversed  is  narrow,  especially  at  its  point  of  entrance  into  the  uterus,  at 
which  it  will  scarcely  admit  a  bristle,  its  other  extremity  is  wider,  and 
opens  into  the  cavity  of  the  abdomen,  surrounded  by  the  zone  of  fimbriae. 
Externally,  the  Fallopian  tube  is  invested  with  peritoneum;  internally, 
its  canal  is  lined  with  mucous  membrane,  covered  with  ciliated  epithe- 
lium: between  the  peritoneal  and  mucous  coats,  the  walls  are  composed, 
like  those  of  the  uterus,  of  fibrous  tissue  and  plain  muscular  fibres. 

Uterus. — The  Uterus  {u,  c,  Fig.  392)  is  somewhat  pyriform,  and  in 
the  unimpregnated  state  is  about  three  inches  in  length,  two  in  breadth 
at  its  upper  part  or  fundus,  but  at  its  lower  pointed  part  or  nec'k,  only 
about  half  an  inch.  The  part  between  the  fundus  and  neck  is  termed 
the  body  of  the  uterus:  it  is  about  an  inch  in  thickness. 

Structure. — The  uterus  is  constructed  of  three  principal  layers,  or 
coats, — serous,  fibrous  and  muscvlar,  and  mucous.  (1.)  The  serous 
coat,  which  luis  the  same  general  structure  as  the  peritoneum,  covers  the 
organ  before  and  behind,  but  is  absent  from  the  front  surface  of  the  neck. 
(2.)  The  middle  coat  is  composed  of  dense  connective  tissue,  with  which 


GENERATIO]Sr  AND  DEVELOPMENT. 


239 


are  intermingled  fibres  of  unstriped  muscle.  The  latter  become  enor- 
mously developed  during  pregnancy.  (3.)  The  mucous  membrane  of  the 
uterus  will  be  described  more  in  detail  presently  (p.  242,  Vol.  II.).  It  is 
lined  by  columnar  ciliated  epithelium,  which  extends  also  into  the  interior 
of  the  tubular  glands,  of  which  the  mucous  membrane  is  largely  made 
up.    (Allen  Thomson,  Nylander,  Friedlander,  John  Williams.) 

The  cavity  of  the  uterus  corresponds  in  form  to  that  of  the  organ 
itself:  it  is  very  small  in  the  unimpregnated  state;  the  sides  of  its  mucous 
surface  being  almost  in  contact,  and  probably  only  separated  from  each 
other  by  mucus.  Into  its  upper  part,  at  each  side,  opens  the  canal  of 
the  corresponding  Fallopian  tube:  below,  it  communicates  with  the 
vagina  by  a  fissure-like  opening  in  its  neck,  the  os  uteri,  the  margins 
of  which  are  distinguished  into  two  lips,  an  anterior  and  posterior.  In 
the  mucous  membrane  of  the  cervix  are  found  several  mucous  follicles, 
termed  ovula  or  glandulge  Nabothi:  they  probably  form  the  jelly-like  sub- 
stance by  which  the  os  uteri  is  usually  found  closed. 

The  vagina  is  a  membranous  canal,  five  or  six  inches  long,  extending 
obliquely  downward  and  forward  from  the  neck  of  the  uterus,  which  it 
embraces,  to  the  external  organs  of  generation.  It  is  lined  with  mucous 
membrane,  which  in  the  ordinary  contracted  state  of  the  canal  is  thrown 
into  transverse  folds.  External  to  the  mucous  membrane  the  walls  of 
the  vagina  are  constructed  of  fibrous  tissue,  within  which,  especially 
around  the  lower  part  of  the  tube,  is  a  layer  of  erectile  tissue.  The 
lower  extremity  of  the  vagina  is  embraced  by  an  orbicular  muscle,  the 
constrictor  vagincs;  its  external  orifice,  in  the  virgin,  is  partially  closed 
by  a  fold  or  ring  of  mucous  membrane,  termed  the  hymen.  The  external 
organs  of  generation  consist  of  the  clitoris,  sl  small  elongated  body,  situ- 
ated above  and  in  the  mdidle  line,  and  constructed,  like  the  male  penis, 
of  two  erectile  corpora  cavernosa,  but  unlike  it,  without  a  corpus  spongi- 
osum, and  not  perforated  by  the  urethra;  of  two  folds  of  mucous  mem- 
brane, termed  labia  interna,  or  nyw^phce;  and,  in  front  of  these,  of  two 
other  folds,  the  laMa  externa,  or  pudenda,  formed  of  the  external  integu- 
ment, and  lined  internally  by  mucous  membrane.  Between  the  nymphae 
and  beneath  the  clitoris  is  an  angular  space,  termed  the  vestibule,  at  the 
centre  of  whose  base  is  the  orifice  of  the  meatus  urinarius.  Numerous 
mucous  follicles  are  scattered  beneath  the  mucous  membrane  composing 
these  parts  of  the  external  organs  of  generation;  and  at  the  side  of  the 
lower  part  of  the  vagina,  are  two  larger  lobulated  glands,  named  vulvo- 
vaginal, or  Duverney's  glands,  which  are  analogous  to  Cowper's  glands  in 
the  male. 

Discharge  of  the  Ovum.— In  the  process  of  development  of  indi- 
vidual Graafian  vesicles,  it  has  been  already  observed,  that  as  each  in- 
creases in  size,  it  gradually  approaches  the  surface  of  the  ovary,  and  when 
fully  ripe  or  mature,  forms  a  little  projection  on  the  exterior.  Coincident 


240 


HAND-BOOK  OF  PHYSIOLOGY. 


with  the  increase  of  size,  caused  by  the  augmentation  of  its  liquid  con- 
tents, the  external  envelope  of  the  distended  vesicle  becomes  very  thin  and 
eventually  bursts.  By  this  means,  the  ovum  and  fluid  contents  of  the 
Graafian  vesicle  are  liberated,  and  escape  on  the  exterior  of  the  ovary, 
whence  they  pass  into  the  Fallopian  tube,  the  fimbriated  processes  of  the 
extremity  of  which  are  supposed  coincidentally  to  grasp  the  ovary,  while 
the  aperture  of  the  tube  is  applied  to  the  part  corresponding  to  the 
matured  and  bursting  vesicle. 

In  animals  whose  capability  of  being  impregnated  occurs  at  regular 
periods,  as  in  the  human  subject,  and  most  Mammalia,  the  Graafian 
vesicles  and  their  contained  ova  appear  to  arrive  at  maturity,  and  the 
latter  to  be  discharged  at  such  periods  only.  But  in  other  animals,  e.g., 
the  common  fowl,  the  formation,  maturation,  and  discharge  of  ova  ap- 
pear to  take  place  almost  constantly.  , 

It  has  long  been  known,  that  in  the  so-called  oviparous  animals^ 
the  separation  of  ova  from  the  ovary  may  take  place  independently  of  im- 
pregnation by  the  male,  or  even  of  sexual  union.  And  it  is  now  estab- 
lished that  a  like  maturation '  and  discharge  of  ova,  independently  of 
coition,  occurs  in  Mammalia,  the  periods  at  which  the  matured  Gva  are 
separated  from  the  ovaries  and  received  into  the  Fallopian  tubes  being 
indicated  in  the  lower  Mammalia  by  the  phenomena  of  heat  or  rut:  in  th& 
human  female,  although  not  always  with  exact  coincidence,  by  the  phe- 
nomena of  menstruation.  If  the  union  of  the  sexes  take  place,  the  ovuni 
may  be  fecundated,  and  if  no  union  occur  it  perishes. 

That  this  maturation  and  discharge  occur  periodically,  and  only  during 
the  phenomena  of  heat  in  the  lower  Mammalia,  is  made  probable  by  tliG 
facts  that,  in  all  instances  in  which  Graafian  vesicles  have  been  found 
presenting  the  appearance  of  recent  rupture,  the  animals  were  at  the  time, 
or  had  recently  been,  in  heat;  that  on  the  other  hand,  there  is  no  authentic 
and  detailed  account  of  Graafian  vesicles  being  found  ruptured  in  the 
intervals  of  the  period  of  heat;  and  that  female  animals  do  not  admit  the 
males,  and  never  become  impregnated,  except  at  those  periods. 

Menstruation. — Many  circumstances  make  it  certain  that  the  human 
female  is  subject,  in  these  respects,  to  the  same  law  as  the  females  of 
other  mammiferous  animals;  namely,  that  in  her  as  in  them,  ova  are 
matured  and  discharged  from  the  ovary  independent  of  sexual  union. 
This  maturation  and  discharge  occur,  moreover,  periodically  at  or  about 
the  epochs  of  menstruation.  Thus  Graafian  vesicles  recently  ruptured 
have  been  frequently  seen  in  ovaries  of  virgins  or  women  who  could  not 
have  been  recently  impregnated;  and  although  it  is  true  that  the  ova  dis- 
charged under  these  circumstances  have  rarely  been  discovered  in  the 
Fallopian  tube,  partly  on  account  of  their  minute  size,  and  partly  because 
the  search  has  seldom  been  prosecuted  with  much  care,  yet  analogy  for- 
bids us  to  doubt  that  in  the  luiman  female,  as  in  the  domestic  quadrupeds, 


GENERATION  AND  DEVELOPMENT. 


241 


the  result  and  purpose  of  the  rupture  of  the  follicles  is  the  discharge  of 
the  ova. 

The  evidence  of  the  periodical  discharge  of  ova  is  that  in  most  cases 
in  which  signs,  of  menstruation  have  been  found  in  the  uterus,  follicles 
in  a  state  of  maturity  or  of  rupture  have  been  seen  in  the  ovary;  and  that 
although  conception  is  not  confined  to  the  periods  of  menstruation,  yet 
it  is  more  likely  to  occur  about  a  menstrual  epoch  than  at  other  times. 

Tlie  exact  relation  between  the  discharge  of  ova  and  menstruation  is 
not  very  clear.  It  was  generally  believed  that  the  monthly  flux  was  the 
result  of  a  congestion  of  the  uterus  arising  from  the  enlargement  and 
rupture  of  a  Graafian  follicle;  but  though  a  Grraafian  follicle  is,  as  a  rule, 
ruptured  at  each  menstrual  epoch,  yet  several  instances  are  recorded  in 
which  menstruation  has  occurred  where  no  Graafian  follicle  has  been  rup- 
tured, and  on  the  other  hand  cases  are  known  where  ova  have  been  dis- 
charged in  amenorrhcBic  women.  It  must  therefore  be  admitted  that 
menstruation  is  not  dependent  on  the  maturation  and  discharge  of  ova. 

It  was,  moreover,  generally  understood  that  ova  were  discharged 
toward  the  close  or  soon  after  the  cessation  of  a  menstrual  flow.  Obser- 
vations made  after  death,  and  facts  obtained  by  clinical  investigation,  how- 
ever, do  not  support  this  view.  (Reichert,  J.  Williams,  Lowenthal.) 
Rupture  of  ^  a  Graafian  follicle  does  not  happen  on  the  same  day  of  the 
monthly  period  in  all  women.  It  may  occur  toward  the  close  or  soon  after 
the  cessation  of  a  flow;  but  only  in  a  small  minority  of  the  subjects  ex- 
amined after  death  was  this  the  case.  On  the  other  hand,  in  almost  all 
such  subjects  of  which  there  is  record,  rupture  of  the  follicle  appears  to 
have  taken  place  before  the  commencement  of  the  catamenial  flow. 
Moreover,  the  custom  of  the  Jews — a  prolific  race,  to  whom  by  the  Levit- 
ical  law  sexual  intercourse  during  the  week  following  menstruation  was 
forbidden — militates  strongly  in  favor  of  the  view  that  conception  usually 
occurs  before  and  not  soon  after  a  menstrual  epoch,  and  necessarily, 
therefore,  for  the  view  that  ova  are  usually  discharged  before  the  cata- 
menial flow.  This,  together  with  the  anatomical  condition  of  the  uterus 
just  before  the  catamenia,  seem  to  indicate  that  the  ovum  fertilized  is 
that  which  is  discharged  in  connection  with  the  first  absent,  and  not  that 
with  the  last  present  menstruation.  (Kundrat.) 

Though  menstruation  does  not  appear  to  depend  upon  the  discharge, 
of  ova,  yet  the  presence  of  the  ovaries  seems  necessary  for  the  perform- 
ance of  the  function;  for  women  do  not  menstruate  when  both  ovaries, 
have  been  removed  by  operation.  Some  instances  have  been  recently 
recorded,  indeed,  of  a  sanguineous  discharge,  occurring  periodically  from 
the  vagina  after  both  ovaries  have  been  previously  removed  for  disease;, 
and  it  has  been  inferred  from  this  that  menstruation  is  a  function  inde- 
pendent of  the  ovary:  but  this  evidence  is  not  conclusive,  inasmuch  as  it. 
is  possible  that  portions  of  ovarian  tissue  were  left  after  the  operation. 
Vol.  II.— 16. 


242 


HAND-BOOK  OF  PHYSIOLOGY. 


Characters  of  Menstrual  Discharge. — The  menstrual  discharge  is 
a  thin  sanguineous  fluid,  having  a  peculiar  odor.  It  is  of  a  dark  color, 
and  consists  of  blood,  epithelium,  and  mucus  from  the  uterus  and  vagina, 
serum,  and  the  debris  of  a  membrane  called  the  decidua  menstrtialis.. 
This  membrane  is  the  developed  mucous  surface  of  the  body  of  the 
uterus.  It  does  not  extend  into  the  Fallopian  tube  or  into  the  cavity  of 
the  cervix.  It  attains  its  highest  state  of  development  in  the  unimpreg- 
nated  organ  just  before  the  commencement  of  a  catamenial  flow  (Fig.  396). 
If  impregnation  take  place,  it  becomes  the  decidua  vera;  if  impregnation 


Fig.  396.  Fig.  397.  Fig.  398. 


Fig.  396.— Diagram  of  uterus  just  before  menstruation;  the  shaded  portion  represents  the  thick- 
ened mucous  membrane. 

Fig.  397.— Diagram  of  uterus  when  menstruation  has  just  ceased,  showing  the  cavity  of  the 
uterus  deprived  of  mucous  membrane. 

Fig.  398.— Diagram  of  uterus  a  week  after  the  menstrual  flux  has  ceased:  the  shaded  portion 
represents  renewed  mucous  membrane.   (J.  Wilhams.) 

fail,  the  membrane  undergoes  rapid  disintegration;  its  vessels  are  laid 
open  and  haemorrhage  follows  (John  Williams).  The  blood  poured  out 
does  not  coagulate  in  consequence  partly  of  the  admixture  already  men- 
tioned, or,  very  possibly,  coagulation  occurs,  but  the  process  is  more  or 
less  spoiled,  and  what  clot  is  formed  is  broken  down  again,  so  as  to  imi- 
tate liquid  blood.    (See  also  p.  73,  Vol.  I.) 

Menstruation,  therefore,  is  not  the  result  of  congestion,  or  of  a  species 
of  erection,  but  of  a  destructive  process  by  which  the  decidua  or  nidus 
prepared  for  an  impregnated  ovum  is  carried  away.  It  is  not  a  sign  of  tlie 
capability  of  being  impregnated  as  much  as  of  disappointed  impregnation. 

The  occurrence  of  a  menstrual  discharge  is  one  of  the  most  prominent 


GENERATION  AND  DEVELOPMENT. 


243 


indications  of  the  commencement  of  puberty  in  the  female  sex;  though 
its  absence  even  for  several  years  is  not  necessarily  attended  with  arrest  of 
the  other  characters  of  this  period  of  life,  or  with  inaptness  for  sexual 
union,  or  incapability  of  impregnation.  The  average  time  of  its  first  ap- 
pearance in  females  of  this  country  and  others  of  about  the  same  latitude, 
is  from  fourteen  to  fifteen;  but  it  is  much  influenced  by  the  kind  of  life 
to  which  girls  are  subjected,  being  accelerated  by  habits  of  luxury  and 
indolence,  and  retarded  by  contrary  conditions.  On  the  whole,  its  ap- 
pearance is  earlier  in  persons  dwelling  in  warm  climes  than  in  those  in- 
habiting colder  latitudes;  though  the  extensive  investigations  of  Eobertson 
show  that  the  influence  of  temperature  on  the  development  of  puberty 
has  been  exaggerated.  Much  of  the  influence  attributed  to  climate 
appears  due  to  the  custom  prevalent  in  many  hot  countries,  as  in  Hin- 
dostan,  of  giving  girls  in  marriage  at  a  very  early  age,  and  inducing  sex- 
ual excitement  previous  to  the  proper  menstrual  time.  The  menstrual 
functions  continue  through  the  whole  fruitful  period  of  a  woman's  life, 
and  usually  cease  between  the  forty-fifth  and  fiftieth  years. 

The  several  menstrual  periods  usually  occur  at  intervals  of  a  lunar 
month,  the  duration  of  each  being  from  three  to  six  days.  In  some 
women  the  intervals  are  as  short  as  three  weeks  or  even  less;  while  in 
others  they  are  longer  than  a  month.  The  periodical  return  is  usually 
attended  by  pain  in  the  loins,  a  sense  of  fatigue  in  the  lower  limbs,  and 
other  symptoms,  which  are  different  in  different  individuals.  Men- 
struation does  not  usually  occur  in  pregnant  women,  or  in  those  who  are 
suckling;  but  instances  of  its  occurrence  in  both  these  conditions  are  by 
no  means  rare. 

COEPUS  LUTEUM. 

Immediately  before,  as  well  as  subsequent  to,  the  rupture  of  a  Graafian 
vesicle,  and  the  escape  of  its  ovum,  certain  changes  ensue  in  the  interior 
of  the  vesicle,  which  result  in  the  production  of  a  yellowish  mass,  termed 
a  Corpus  luteum. 

When  fully  formed  the  corpus  luteum  of  mammiferous  animals  is  a 
roundish  solid  body,  of  a  yellowish  or  orange  color,  and  composed  of  a 
number  of  lobules,  which  surround,  sometimes  a  small  cavity,  but  more 
frequently  a  small  stelliform  mass  of  white  substance,  from  which  delicate 
processes  pass  as  septa  between  the  several  lobules.  Very  often,  in  the 
cow  and  sheep,  there  is  no  white  substance  in  the  centre  of  the  corpus 
luteum;  and  the  lobules  projecting  from  the  opposite  walls  of  the  Graafian 
vesicle  appear  in  a  section  to  be  separated  by  the  thinnest  possible  lamina 
of  semi-transparent  tissue. 

"When  a  Graafian  vesicle  is  about  to  burst  and  expel  the  ovum,  it  be- 
comes highly  vascular  and  opaque;  and,  immediately  before  the  rupture 


244 


HAND-BOOK  OF  PHYSIOLOGY. 


takes  place,  its  walls  appear  thickened  on  the  interior  by  a  reddish  gluti- 
nous or  fleshy-looking  substance.  Immediately  after  the  rupture,  the 
inner  layer  of  the  wall  of  the  vesicle  appears  pulpy  and  flocculent.  It  is 
thrown  into  wrinkles  by  the  contraction  of  the  outer  layer,  and,  soon, 
red  fleshy  mamniillary  processes  grow  from  it,  and  gradually  enlarge  till 
they  nearly  fill  the  vesicle,  and  even  protrude  from  the  orifice  in  the  ex- 
ternal covering  of  the  ovary.  Subsequently  this  orifice  closes,  but  the 
fleshy  growth  within  still  increases  during  the  earlier  period  of  pregnancy, 
the  color  of  the  substance  gradually  changing  from  red  to  yellow,  and  its 
consistence  becoming  firmer. 

The  corpus  luteum  of  the  human  female  (Fig.  .399)  differs  from  that 
of  the  domestic  quadruped  in  being  of  a  firmer  texture,  and  having  more 
frequently  a  persistent  cavity  at  its  centre,  and  in  the  stelliform  cicatrix, 
which  remains  in  the  cases  where  the  cavity  is  obliterated,  being  propor- 
tionately of  much  larger  bulk.    The  quantity  of  yellow  substance  formed 


Fig.  399.— Corpora  lutea  of  different  periods,  b,  Corpus  luteum  of  about  the  sixth  week  after 
impregnation,  showing  its  plicated  form  at  that  period.  1,  substance  of  the  ovary;  2,  substance  of 
the  corpus  luteum;  3,  a  greyish  coagulum  in  its  cavity.  (Peterson.)  a,  corpus  luteum  two  days  after 
delivery;  d,  in  the  twelfth  week  after  deUvery.  (Montgomery.) 

is  also  much  less:  and,  although  the  deposit  increases  after  the  vesicle  has 
burst,  yet  it  does  not  usually  form  mamniillary  growths  projecting  into 
the  cavity  of  the  vesicle,  and  never  protrudes  from  the  orifice,  as  is  the 
case  in  other  Mammalia.  It  maintains  the  character  of  a  uniform,  or 
nearly  uniform,  layer,  which  is  thrown  into  wrinkles,  in  consequence  of 
the  contraction  of  the  external  tunic  of  the  vesicle.  After  the  orifice  of  the 
vesicle  has  closed,  the  growth  of  the  yellow  substance  continues  during  the 
first  half  of  pregnancy,  till  the  cavity  is  reduced  to  a  comparatively  small 
size,  or  is  obliterated;  in  the  latter  case,  merely  a  white  stelliform  cicatrix 
remains  in  the  centre  of  the  corpus  luteum. 

An  effusion  of  blood  generally  takes  place  into  the  cavity  of  the 
Graafian  vesicle  at  the  time  of  its  rupture,  especially  in  the  human  sub- 
ject, but  it  has  no  share  in  forming  the  yellow  body;  it  gradually  loses 
its  coloring  matter,  and  acquires  the  character  of  a  mass  of  fibrin.  The 
serum  of  the  blood  sometimes  remains  included  within  a  cavity  in  the 
centre  of  the  coagulum,  and  then  the  decolorized  fibrin  forms  a  mem- 


GENERATION  AND  DEVELOPMENT. 


245 


braniform  sac,  lining  the  corpus  luteum.  At  other  times  the  serum  is  re- 
moved, and  the  fibrin  constitutes  a  solid  stelliform  mass. 

The  yellow  substance  of  which  the  corpus  luteum  consists,  both  in 
the  human  subject  and  in  the  domestic  animals,  is  a  growth  from  the 
inner  surface  of  the  Graafian  vesicle,  the  result  of  an  increased  develop- 
ment of  the  cells  forming  the  membrana  granulosa,  which  naturally  lines 
the  internal  tunic  of  the  vesicle. 

The  first  changes  of  the  internal  coat  of  the  Graafian  vesicle  in  the 
process  of  formation  of  a  corpus  luteum,  seem  to  occur  in  every  case  in 
which  an  ovum  escapes;  as  well  in  the  human  subject  as  in  the  domestic 
quadrupeds.  If  the  ovum  is  impregnated,  the  growth  of  the  yellow  sub- 
stance continues  during  nearly  the  whole  period  of  gestation,  and  forms 
the  large  corpus  luteum  commonly  described  as  a  characteristic  mark  of 
impregnation.  If  the  ovum  is  not  impregnated,  the  growth  of  yellow 
substance  on  the  internal  surface  of  the  vesicle  proceeds,  in  the  human 
ovary,  no  further  than  the  formation  of  a  thin  layer,  which  shortly  disap- 
pears; but  in  the  domestic  animals  it  continues  for  some  time  after  the 
ovum  has  perished,  and  forms  a  corpus  luteum  of  considerable  size.  The 
fact  that  a  structure,  in  its  essential  characters  similar  to,  though  smaller 
than,  a  corpus  luteum  observed  during  pregnancy,  is  formed  in  the 
human  subject,  independent  of  impregnation  or  of  sexual  union,  coupled 
with  the  varieties  in  size  of  corpora  lutea  formed  during  pregnancy,  neces- 
sarily renders  unsafe  all  evidence  of  previous  impregnation  founded  on 
the  existence  of  a  corpus  luteum  in  the  ovary. 

The  following  table  by  Dalton,  expresses  well  the  differences  between 
the  corpus  luteum  of  the  pregnant  and  unimpregnated  condition  re- 
spectively. 


CoRPEUs  Luteum  of 
Menstruation 


Corpus  Luteum  op  Preg- 
nancy. 


At  tlie  end  of 

three  weeks. 
One  montli  .  . 


Tim  months 
Six  months  . 
Nine  months 


Three-quarters  of  an  inch  in  diameter  ;  central  clot  red- 
dish ;  convoluted  wall  pale. 


Smaller  ;  convoluted 
wall  bright  yellow ; 
clot  still  reddish. 

Eeduced  to  the  con- 
dition of  an  insig- 
nificant cicatrix. 

Absent. 


Absent. 


Larger  ;  convoluted  wall  bright 
yellow  ;  clot  still  reddish. 

Seven-eighths  of  an  inch  in  diame- 
ter; convoluted  wall  bright  yel- 
low ;  clot  perfectly  decolorized. 

Still  as  large  as  at  end  of  second 
month  ;  clot  fibrinous  ;  convo- 
luted wall  paler. 

One-half  an  inch  in  diameter  ; 
central  clot  converted  into  a 
radiating  cicatrix  ;  the  external 
wall  tolerably  thick  and  convo- 
luted, but  without  any  bright 
yellow  color. 


246 


HAND-BOOK  OF  PHYSIOLOGY. 


IMPEEGNATION  OF  THE  OVUM. 
Male  Sexual  Functioi^s. 

Testes. — The  fluid  of  the  male,  by  which  the  ovum  is  impregnated, 
consists  essentially  of  the  semen  secreted  by  the  testicles:  and  to  this  are 
added,  as  necessary,  perhaps,  to  its  perfection,  a  material  secreted  by  the 
vesiculcB  seminales,  as  well  as  the  secretion  of  the  prostate  gland,  and  of 
Cowper^s  glands.  Portions  of  these  several  fluids  are,  probably,  all  dis- 
charged, together  with  the  proper  secretion  of  the  testicles. 

The  secreting  structure  of  the  testicle  and  its  duct  are  disposed  of  in 
two  contiguous  parts,  (1)  the  body  of  the  testicle  enclosed  within  a  tough 


Fig.  400.  Fig.  401. 

Fig.  400.— Section  of  a  dog's  epididymis.  The  tube  is  cut  in  several  places,  both  transversely  and 
obliquely;  it  is  seen  to  be  lined  by  a  ciliated  epithelium,  the  nuclei  of  which  are  well  shown,  c,  con- 
nective tissue.  (Schofield.) 

Fig.  401.— a  section  of  dog's  testicle,  highly  magnified,  showing  three  "tubuli  semiuiferi,"  lined 
and  largely  occupied  by  a  spheroidal  epithelium,  the  mmierous  nuclei  of  which  are  well  seen;  c,  con- 
nective tissue  surrounding  and  supporting  the  tubuli;  sp,  masses  of  spermatozoa  occupying  the 
centre  of  tubuH:  the  small  black  bodies  scattered  about  are  the  heads  of  the  spermatozoa.  (Scho- 
field.) 

fibrous  membrane,  the  tunica  albuginea,  on  the  outer  surface  of  which 
is  the  serous  covering  formed  by  the  tunica  vaginalis,  and  (2)  the  epi- 
didymis and  vas  (lofercns. 

Vas  Deferens. — The  vas  deferens,  or  duct  of  the  testicle,  which  is 
about  two  feet  in  length,  is  constructed  externally  of  connective  tissue,  and 
internally  is  lined  by  mucous  membrane,  covered  by  columnar  epithe- 
lium; while  between  these  two  coats  is  a  middle  coat,  very  firm  and 


GENERATION  AND  DEVELOPMENT. 


247 


tough,  made  up  chiefly  of  longitudinal  with  some  circular  plain  muscular 
fibres.  When  followed  back  to  its  origin,  the  vas  deferens  is  found  to 
pass  to  the  lower  part  of  the  epididymis,  with  which  it  is  directly  con- 
tinuous (Fig.  402),  and  assumes  there  a  much  smaller  diameter  with  an 
exceedingly  tortuous  course. 

The  epididym  is,  which  is  lined,  except  at  its  lowest  part,  by  columnar 
ciliated  epithelium  (Fig.  400),  is  commonly  described  as  consisting  (Fig. 
402)  of  a  globus  minor  (g),  the  body  (e),  and  the  globus  major  (l).  When 
unraveled,  it  is  found  to  be  constructed  of  a  single  tube,  measuring 
about  twenty  feet  in  length. 

At  the  globus  major  this  duct  divides  into  ten  or  twelve  small  branches, 
the  convolutions  of  which  form  coniform  masses,  named  coni  vasculosi; 
and  the  ducts  continued  from  these,  the  vasa  efferentia,  after  anastomos- 
ing, one  with  another,  in  what  is  called  the  rete  testis,  lead  finally  as  the 
tubuli  recti  or  vasa  recta  to  the  tubules  which  form  the  proper  substance 
of  the  testicle,  wherein  they  are  arranged  in  lobules,  closely  packed,  and 
all  attached  to  the  tough  fibrous  tissue  at  the  back  of  the  testicle.  The 
epithelium  of  the  coni  vasculosi  and  vasa  efferentia  is  columnar  and  cili- 
ated; that  of  the  rete  testis  is  squamous. 

Structure  of  Seminal  Tubes. — The  seminal  tubes,  or  tuhuli  sem- 
iniferi,  which  compose  the  parenchyma  of  the  testicle,  are  arranged  in 
lobules  between  the  connective  tissue  septa. 

They  are  relatively  large,  very  wavy,  and  much  convoluted;  and  they 
possess  a  few  lateral  branches,  by  which  they  become  connected  into  a  net- 
work. They  form  terminal  loops,  and  in  the  peripheral  portion  of  the 
testis  the  tubules  are  possessed  of  minute  lateral  caecal  branchlets. 

Each  seminal  tubule  in  the  adult  testis  is  limited  by  a  membrana  pro- 
pria, which  appears  as  a  hyaline  elastic  membrane  containing  oval  flat- 
tened nuclei  at  regular  intervals.  Inside  this  membrana  propria  are 
several  layers  of  epithelial  cells,  the  seminal  cells.  These  consist  of  an 
inner  and  outer  layer,  the  latter  being  situated  next  the  membrana  pro- 
pria. These  cells  are  of  two  kinds,  those  that  are  in  a  resting  state  and 
those  that  are  in  a  state  of  division.  The  latter  are  called  mother  cells, 
and  the  smaller  cells  resulting  from  their  division  are  called  daughter 
cells  or  spermatoblasts.  From  these  the  spermatozoa  are  formed.  During 
their  development  they  lie  in  groups,  but  when  fully  formed  they  become 
detached  and  fill  the  lumen  of  the  seminiferous  tubule  (Fig.  491). 

Spermatozoa. — On  examining  the  spermatozoon  of  Triton  cristatus, 
one  of  the  Amphibia  which  possess  the  largest  of  all  Vertebrate  animals, 
Heneage  G-ibbes  found  that  the  org;anism  (Fig.  404)  consisted  of  (a)  a 
long  pointed  head,  at  the  base  of  which  is  {b),  an  elliptical  structure  join- 
ing the  head  to  (c),  a  long  filiform  body;  (d),  a  fine  filament,  much  longer 
than  the  body,  is  connected  with  this  latter  by  (e),  a  homogeneous  mem- 
brane. 


248 


HAND-BOOK  OF  PHYSIOLOGY. 


The  head,  as  it  appears  in  the  fresh  specimen,  has  a  different  refrac- 
tive power  from  that  of  the  rest  of  the  organism,  and  with  a  high  power 
appears  to  be  a  light  green  color;  there  is  also  a  central  line  running  up 
it,  from  which  it  appears  to  be  hollow.  The  elliptical  structure  at  the 
base  of  the  head  connects  it  with  the  long  thread-like  body,  and  the  fila- 
ment springs  from  it.  Whilst  the  spermatozoon  is  living,  this  filament 
is  in  constant  motion;  at  first  this  is  so  quick  that  it  is  difficult  to  see  it, 
but  as  its  vitality  becomes  impaired  the  motion  gets  slower,  and  it  is  then 
easily  perceived  to  be  a  continuous  waving  from  side  to  side. 

In  Man  the  head  (Fig.  405)  is  club-shaped,  and  from  its  base  springs 
the  very  delicate  filament  which  is  three  or  four  times  as  long  as  the 


Fig.  402.  Fig.  403. 


Fig.  402. — Plan  of  a  vertical  section  of  the  testicle,  showing  the  arrangement  of  the  ducts.  The 
true  length  and  diameter  of  the  ducts  have  been  disregarded,  a,  a.  tubuli  seminiferi  coiled  up  in 
the  separate  lobes;  6,  tubuli  recti  or  vasa  recta;  c,  rete  testis;  d,  vasa  efferentia  ending  in  the  coni 
vasculosi;  I,  e,  g,  convoluted  canal  of  the  epididymis;  h,  vas  deferens;  /,  section  of  the  back  part 
of  the  timica  albuginea;  i,  i,  fibrous  processes  running  between  the  lobes;  s,  mediastinum. 

Fig.  403.— Spermatic  filaments  from  the  human  vas  deferens.  1,  magnified  350  diameters;  2, 
magnified  800  diameters;  a,  from  the  side;  6,  from  above.   (From  KoUiker.) 

body;  and  the  membrane  which  attaches  it  to  the  body  is  much  broader, 
and  allows  it  to  lie  at  a  greater  distance  from  the  body  than  in  the  sperma- 
tozoa of  any  other  Mammal  examined. 

Gibbes  concludes: — 1st.  That  the  head  of  the  spermatozoon  is  enclosed 
in  a  sheath,  which  is  a  continuation  of  the  membrane  which  surrounds 
the  filament  and  connects  it  to  the  body,  acting  in  fact  the  part  of  a  mes- 
entery. 2ndly.  That  the  substance  of  the  head  is  quite  distinct  in  its 
composition  from  the  elliptical  structure,  the  filament  and  the  long  bod}', 
and  that  it  is  readily  acted  upon  by  alkalies;  these  re-agents  have  no 
effect,  however,  on  the  other  part,  excepting  the  membranous  sheath. 
3rdly.  That  this  elliptical  structure  has  its  analogue  in  the  Mammalian 
spermatozoon;  in  the  one  case  the  head  is  drawn  out  as  a  long  pointed 
process,  in  the  other  it  is  of  a  globular  form,  and  surrounds  the  elliptical 
structure.  4thly.  That  the  motive  power  lies,  in  a  great  measure,  in 
tlio  filament  and  the  membrane  attacliing  it  to  the  body. 

The  occurrence  of  spermatozoa  in  the  impregnating  fiuid  of  nearly  all 
classes  of  animals  proves  that  they  are  essential  to  the  process  of  impreg- 


GENERATION  AND  DEVELOPMENT. 


249 


nation,  and  their  actual  contact  with  the  ovum  is  necessary  for  its  devel- 
opment; but  concerning  the  manner  of  their  action  nothing  is  known. 

The  seminal  fluid  is,  probably,  after  the  period  of  puberty,  secreted 
constantly,  though,  except  under  excitement,  very  slowly,  in  the  tubules 
of  the  testicles.  From  these,  it  passes  along  the  vasa  deferentia  into  the 
vesiculse  seminales,  whence,  if  not  expelled  in  emission,  it  may  be  dis- 


FiG.  404.  Fig.  405, 

Fig.  404.— Spermatozoon  of  Salamandra  Maculata.  Fresh  mounted  in  glycerin,  x  950,  reduced 
one  half. 

Fig.  405.— Human  Spermatozoa,    x  2500.   (H.  Gibbes.) 

charged,  as  slowly  as  it  enters  them,  either  with  the  urine,  which  may 
remove  minute  quantities,  mingled  with  the  mucus  of  the  bladder  and 
the  secretion  of  the  prostate,  or  from  the  urethra  in  the  act  of  defaecation. 

Vesiculae  Seminales. — The  vesiculce  seminales  (Fig.  406)  have  the 
appearance  of  outgrowths  from  the  vasa  deferentia.    Each  vas  deferens, 


250 


HAND-BOOK  OF  PHYSIOLOGY. 


just  before  it  enters  tlie  prostate  gland,  through  part  of  which  it  passes 
to  terminate  in  the  urethra,  gives  oS  a  side-branch,  which  bends  back 
from  it  at  an  acute  angle:  and  this  branch  dilating,  variously  branching, 
and  pursuing  in  both  itself  and  its  branches  a  tortuous  course,  forms  the 
vesicula  seminalis. 

Structure. — Each  of  the  vesiculse,  therefore,  might  be  unraveled 
into  a  single  branching  tube,  sacculated,  convoluted,  and  folded  up.  The 
structure  of  the  vesiculse  resembles  closely  that  of  the  vasa  deferentia. 
The  mucous  membrane  lining  the  vesiculae  seminales,  like  that  of  the 
gall-bladder,  is  minutely  wrinkled  and  set  with  folds  and  ridges  arranged 
so  as  to  give  it  a  finely  reticulated  appearance. 

Functions. — To  the  vesiculae  seminales  a  double  function  may  be 
assigned;  for  they  both  secrete  some  fluid  to  be  added  to  that  of  the  tes- 


FiG.  406.— Dissection  of  the  base  of  the  bladder  and  prostate  gland,  showing  the  vesicula?  seminales 
and  vasa  deferentia.  o,  lower  surface  of  the  bladder  at  the  place  of  reflection  of  the  peritoneum;  &, 
the  part  above  covered  by  the  peritoneum;  ?,  left  vas  deferens,  ending  in  e,  the  ejaculatory  duct;  the 
vas  deferens  has  been  divided  near  «,  and  all  except  the  vesicle  portion  has  been  taken  away;  s,  left 
vesicula  seminalis  joining  the  same  duct;  .s,  s,  the  right  vas  deferens  and  ri^ht  vesicula  seminalis, 
which  has  been  unraveled;  p,  under  side  of  the  prostate  gland;  m,  part  ot  the  urethra;  u,  m,  the 
ureters  (cut  short),  the  right  one  tm-ned  aside.  (Haller.) 

tides,  and  serve  as  reservoirs  for  the  seminal  fluid.  The  former  is  their 
most  constant  and  probably  most  important  office;  for  in  the  horse,  bear, 
guinea-pig,  and  several  other  animals,  in  whom  the  vesiculj^  seminales 
are  large  and  of  apparently  active  function,  they  do  not  communicate 
with  the  vasa  deferentia,  but  pour  their  secretions,  separately,  thoiigli  it 
may  be  simultaneously,  into  tlie  urethra.  In  man,  also,  when  one  testicle 
is  lost,  the  corresponding  vesicula  seminalis  suffers  no  atrophy,  though  its 
function  as  a  reservoir  is  abrogated.  But  liow  the  vesicula?  seminales  act 
as  secreting  organs  is  unknown;  the  peculiar  brownish  fluid  which  tliey 


GENERATION  AND  DEVELOPMENT. 


251 


contain  after  death  does  not  properly  represent  their  secretion,  for  it  is 
diilerent  in  appearance  from  anything  discharged  during  life,  and  is 
mixed  with  semen.  It  is  nearly  certain,  however,  that  their  secretion 
contributes  to  the  proper  composition  of  the  impregnating  fluid;  for  in 
all  the  animals  in  whom  they  exist,  and  in  whom  the  generative  functions 
are  exercised  at  only  one  season  of  the  year,  the  vesiculae  seminales, 
whether  they  communicate  with  the  vasa  deferentia  or  not,  enlarge  com- 
mensurately  with  the  testicles  at  the  approach  of  that,  season. 

That  the  vesiculae  are  also  reservoirs  in  which  the  seminal  fluid  may 
lie  for  a  time  previous  to  its  discharge,  is  shown  by  their  commonly  con- 
taining the  seminal  filaments  in  larger  abundance  than  any  portion  of  the 
seminal  ducts  themselves  do.  The  fluid-like  mucus,  also,  which  is  often 
discharged  from  the  vesiculas  in  straining  during  defsecation,  commonly 
contains  seminal  filaments.  But  no  reason  can  be  given  why  this  office 
of  the  vesiculae  should  not  be  equally  necessary  to  all  the  animals  whose 
testicles  are  organized  like  those  of  man,  or  why  in  many  animals  the 
vesiculae  are  wholly  absent. 

There  is  an  equally  complete  want  of  information  respecting  the  secre- 
tions of  the  prostate  and  Oowper^s  glands,  their  nature  and  purposes. 
That  they  contribute  to  the  right  composition  of  the  impregnating  fluid, 
is  shown  both  by  the  position  of  the  glands  and  by  their  enlarging  with 
the  testicles  at  the  approach  of  an  animaFs  breeding  time.  But  that  they 
contribute  only  a  subordinate  part  is  shown  by  the  fact,  that,  when  the 
testicles  are  lost,  though  these  other  organs  be  perfect,  all  procreative 
power  ceases. 

The  Semen. 

The  mingled  secretions  of  all  the  organs  just  described,  form  the 
.  semen,  which  is  a  thick  whitish  fluid  composed  of  a  liquor  seminis  and 
spermatozoa,  with  detached  epithelial  cells.  The  fluid  part  has  not 
been  satisfactorily  analyzed:  but  Henle  says  it  contains  fibrin,  because 
shortly  after  being  discharged,  flocculi  form  in  it  by  spontaneous  coagu- 
lation, and  leave  the  rest  of  it  thinner  and  more  liquid,  so  that  the  flla- 
ments  move  in  it  more  actively. 

Nothing  has  shown  what  it  is  that  makes  this  fluid  with  its  corpuscles 
capable  of  impregnating  the  ovum,  or  (what  is  yet  more  remarkable)  of 
giving  to  the  developing  offspring  all  the  characters,  in  features,  size, 
mental  disposition,  and  liability  to  disease,  which  belong  to  the  father. 
This  is  a  fact  wholly  inexplicable:  and  is,  perhaps,  only  exceeded  in 
strangeness  by  those  facts  which  show  that  the  seminal  fluid  may  exert 
such  an  influence,  not  only  on  the  ovum  which  it  impregnates,  but, 
through  the  medium  of  the  mother,  on  many  which  are  subsequently  im- 
pregnated by  the  seminal  fluid  of  another  male. 


252 


HAND-BOOK  OF  PHYSIOLOGY. 


It  lias  been  often  observed  that  a  well-bred  bitch,  if  she  have  been 
once  impregnated  by  a  mongrel  dog,  will  not  bear  thorough-bred  puppies 
in  the  next  two  or  three  litters  after  that  succeeding  the  copulation  with 
the  mongrel.  But  the  best  instance  of  the  kind  was  in  the  case  of  a  mare 
belonging  to  Lord  Morten,  who,  while  he  was  in  India,  wished  to  obtain 
a  cross-breed  between  the  horse  and  the  quagga,  and  caused  this  mare  to 
be  covered  by  a  male  quagga.  The  foal  that  she  next  bore  had  the  dis- 
tinct marks  of  the  quagga,  in  the  shape  of  its  head,  black  bars  on  the  legs 
and  shoulders,  and  other  characters.  After  this  time  she  was  thrice  cov- 
ered by  horses,  and  every  time  the  foal  she  bore  had  still  distinct,  though 
decreasing,  marks  of  the  quagga;  the  peculiar  characters  of  the  quagga 
being  thus  impressed  not  only  on  the  ovum  then  impregnated,  but  on  the 
three  following  ova  impregnated  by  horses.  It  would  appear,  therefore, 
that  the  constitution  of  an  impregnated  female  may  become  so  altered 
and  tainted  with  the  peculiarities  of  the  impregnating  male,  through 
the  medium  of  the  foetus,  that  she  necessarily  imparts  such  peculiarities 
to  any  offspring  she  may  subsequently  bear  by  other  males.  Of  the  direct 
means  by  which  a  peculiarity  of  structure  on  the  part  of  a  male  is  thus 
transmitted,  nothing  whatever  is  known. 

As  bearing  upon  this  subject,  the  following  note  kindly  given  to  the 
Editors  by  Mr.  S.  Probart  may  be  added: — On  the  Farm  Well  wood,  the 

property  of  Charles  R  ,  Esq.,  in  the  Division  of  Graaff  Remet,  Cape 

of  Good  Hope,  there  is  at  present  running  an  aged  mare  with  a  numer- 
ous progeny.  Some  years  ago  she  foaled  for  three  successive  seasons  to  a 
donkey;  after  that  she  gave  birth  to  a  mare  foal,  to  a  horse.  This  filly 
was  a  chestnut,  and  did  not  exhibit  any  taint  of  the  donkey  by  which  her 
dam  had  previously  foaled.  But  when  she  in  her  turn  foaled  to  a  horse, 
her  young  bore  the  distinct  marks  along  the  back  and  withers,  and  rings 
round  the  lower  parts  of  the  legs,  which  are  the  peculiarity  of  the  ass  and 
the  mule.    Three  foals  she  has  had  are  all  so  marked. 

Development. — Changes  in  the  Ovum  up  to  fokmation  of  the 

Blastoderm. 

The  earlier  stages  in  development  are  so  fundamentally  similar  in  all 
vertebrate  animals,  from  Fishes  up  to  Man,  that  the  gaps  existing  in  our 
knowledge  of  the  process  in  the  higher  Mammalia,  such  as  man,  may  be 
in  part,  at  any  rate,  filled  up  by  the  more  accurate  knoAvledge  which  we 
possess  of  the  development  of  the  ovum  in  such  animals  as  the  trout,  frog, 
and  fowl. 

One  important  distinction  between  the  ova  of  various  Vertebrata  should 
be  remembered.  In  the  hen's  egg,  besides  the  shell  and  the  white  or  al- 
bumen, two  other  structures  are  to  bo  distinguished — i\\Qgermy  often  called 
the  cicatricula  or  "tread,"  and  the  ycIk  enclosed  in  its  vitelline  membrane. 

The  (lerm  is  essentially  a  cc^ll,  consisting  of  protoplasm  enclosed  in  a  nu- 
cleus and  nucleolus.  It  nJono  i)articipatos  in  tlio  process  of  segminifat ion 
(to  be  inunediatcily  described),  the  great  mass  of  the  yelk  (food-yelk)  re- 
maining (iiiite  unaffected  l)y  it.  Since  only  the  germ,  which  forms  but  a 
small  portion  of  the  yelk,  undergoes  segmentation,  the  ovum  is  called 
lurrohlasl  ic. 


GENERATIOJSr  AND  DEVELOPMENT. 


253 


In  the  Mammalia,  on  the  other  hand,  there  is  no  large  unsegmcnted 
mass  corresponding  to  the  food-yelk  of  birds;  the  entire  ovum  undergoes 
segmentation,  and  is  hence  termed  lioloblastic. 

The  eggs  of  Fishes,  Reptiles,  and  Birds,  are  meroblastic,  while  those  of 
Amphibia  and  Mammalia  are  lioloblastic. 

Of  the  changes  which  the  mammalian  ovum  undergoes  previous  to  the 
formation  of  the  embryo,  some  occur  while  it  is  still  in  the  ovary,  and  are 
apparently  independent  of  impregnation:  others  take  place  after  it  has 
reached  the  Fallopian  tube.  The  knowledge  we  possess  of  these  changes 
is  derived  almost  exclusively  from  observations  on  the  ova  of  the  bitch  and 
rabbit:  but  it  may  be  inferred  that  analogous  changes  ensue  in  the  human 
ovum. 

Bischoff  describes  the  yelk  of  an  ovarian  ovum  soon  after  coitus  as  being 
unchanged  in  its  characters,  with  the  single  exception  of  being  fuller  and 
more  dense;  it  is  still  granular,  as  before,  and  does  not  possess  any  of  the 
cells  subsequently  found  in  it.  The  germinal  vesicle  always  disappears, 
sometimes  before  the  ovum  leaves  the  ovary,  at  other  times  not  until  it 
has  entered  the  Fallopian  tube;  but  always  before  the  commencement  of 
the  metamorphosis  of  the  yelk. 

As  the  ovum  approaches  the  middle  of  the  Fallopian  tube,  it  begins  to 
receive  a  new  investment,  consisting  of  a  layer  of  transparent  albuminous 
or  glutinous  substance,  which  forms  upon  the  exterior  of  the  zona  pellucida. 
It  is  at  first  exceedingly  fine,  and,  owing  to  this,  and  to  its  transparency, 
is  not  easily  recognized:  but  at  the  lower  part  of  the  Fallopian  tube  it  ac- 
quires considerable  thickness. 

Segmentation. — The  first  visible  result  of  fertilization  is  a  slight 
amceboid  movement  in  the  protoplasm  of  the  ovum:  this  has  been  observed 
in  some  fish,  in  the  frog,  and  in  some  mammals.  Immediately  succeeding 
to  this  the  process  of  segmentation  commences,  and  is  completed  during 
the  passage  of  the  ovum  through  the  Fallopian  tube.  The  yelk  becomes 
constricted  in  the  middle,  and  surrounded  by  a  furrow  which,  gradually 
deepening,  at  length  cuts  the  yelk  in  half  while  the  same  process  begins 
almost  immediately  in  each  half  of  the  yelk,  and  cuts  it  also  in  two.  The 
same  process  is  repeated  in  each  of  the  quarters,  and  so  on,  until  at  last  by 
continual  cleavings  the  whole  yelk  is  changed  into  a  mulberry-like  mass 
of  small  and  more  or  less  rounded  bodies,  sometimes  called  "vitelline 
spheres, the  whole  still  enclosed  by  the  zona  pellucida  or  vitelline  mem- 
brane (Fig.  406*).  Each  of  these  little  spherules  contains  a  transparent 
vesicle  like  an  oil-globule,  which  is  seen  with  difficulty  on  account  of  its 
being  enveloped  by  the  yelk-granules  which  adhere  closely  to  its  surface. 

The  cause  of  this  singular  subdivision  of  the  yelk  is  quite  obscure: 
though  the  immediate  agent  in  its  production  seems  to  be  the  central 
vesicle  contained  in  each  division  of  the  yelk.  Originally  there  was  prob- 
ably but  one  vesicle,  situated  in  the  centre  of  the  entire  granular  mass 


254 


HAND-BOOK  OF  PHYSIOLOGY. 


of  the  yelk,  and  probably  derived  from  the  germinal  vesicle.  This  divides 
and  subdivides:  each  successive  division  and  subdivision  of  the  vesicle 
being  accompanied  by  a  corresponding  division  of  the  yelk. 

About  the  time  at  which  the  Mamma- 
lian ovum  reaches  the  uterus,  the  process  of 
division  and  subdivision  of  the  yelk  appears 
to  have  ceased,  its  substance  having  been 
resolved  into  its  ultimate  and  smallest  divi- 
sions, while  its  surface  presents  a  uniform 
finely-granular  aspect,  instead  of  its  late 
mulberry-like  appearance.  The  ovum,  in- 
deed, appears  at  first  sight  to  have  lost  all 
trace  of  the  cleaving  process,  and,  with  the 
exception  of  being  paler  and  more  trans- 
lucent, almost  exactly  resembles  the  ova- 
rian ovum,  its  yelk  consisting  apparently  of 
a  confused  mass  of  finely  granular  sub- 
stance. But  on  a  more  careful  examina- 
tion, it  is  found  that  these  granules  are 
aggregated  into  numerous  minute  sj)he- 
roidal  masses,  each  of  which  contains  a  clear 
vesicle  or  nucleus  in  its  centre,  and  is,  in 
fact,  an  "embryonal  cell."''  The  zona  pel- 
lucid a,  and  the  layer  of  albuminous  matter 
surrounding  it,  have  at  this  time  the  same 
character  as  when  at  the  lower  part  of  the 
Eallopian  tube. 

The  passage  of  the  ovum,  from  the  ovary 
to  the  uterus,  occupies  probably  eight  or 
ten  days  in  the  human  female. 

When  the  peripheral  cells,  which  are 
formed  first,  are  fully  developed,  they 
arrange  themselves  at  the  surface  of  the 
yelk  into  a  kind  of  membrane,  and  at  the 
same  time  assume  a  polyhedral  shape  from 
mutual  pressure,  so  as  to  resemble  pave- 
ment epithelium.  The  deeper  cells  of  the 
interior  pass  gradually  to  the  surface  and 
accumulate  there,  thus  increasing  the  thick- 
ness of  the  membrane  already  formed  by  the  more  superficial  layer  of 
cells,  while  tlie  central  part  of  the  yelk  remains  filled  only  with  a  clear 
fluid.  15y  this  means  tlie  yelk  is  shortly  converted  into  a  kind  of  secondary 
vesicle,  tlie  walls  of  which  are  composed  externally  of  the  original  vitelline 
membrane,  and  within  by  the  newly  formed  cellular  layer,  the  Mastodermic 
or  (/f'niii)i((I  nuMnl)i-aiu\  as  it  is  called. 


Fig.  406*.— Diagrams  of  the  various 
stages  of  cleavage  of  the  yelk  (Dalton). 


GENERATION  AND  DEVELOPMENT. 


Layers  of  the  Blastoderm. — Before  long  the  blastoderm  is  found  to 
consist  of  three  fundamental  layers,  Epiblast,  MesoUast,  and  Hypoblast. 

The  way  in  which  these  are  formed  may  be  readily  studied  in  a  hen^s 
egg.  In  a  freshly  laid  hen's  egg,  before  incubation  has  commenced,  the 
blastoderm  is  found  to  consist  of  two  layers  (Fig.  407,  8  and  D),  the  upjoer 
of  which  forms  a  distinct  membrane  of  columnar  cells,  while  the  lower 
stratum  consists  of  larger  cells  irregularly  arranged. 


Fi&.  407.— Vertical  section  of  area  pellucida,  and  area  opaca  (left  extremity  of  figure)  of  blasto- 
derm of  a  fresh-laid  egg  (unincubated).  S,  superficial  layer  corresponding  to  epiblast;  D,  deeper 
layer,  corresponding  to  hypoblast,  and  probably  in  part  to  mesoblast;  Jf,  large  "formative  ceUs,'" 
filled  with  yelk  granules,  and  lying  on  the  floor  of  the  segmentation  cavity;  A,  the  white  yelk  im- 
mediately underlying  the  segmentation  cavity  (Strieker). 

Beneath  the  blastoderm  there  are  a  few  scattered  larger  cells — "for- 
mative cells."'  In  the  lower  of  the  above  two  layers,  some  cells  become 
flattened  and  unite  to  form  a  distinct  membrane  (hypoblast);  the  re- 
maining cells  of  the  lower  layer,  together  with  some  of  the  large  formative 


Fig.  408.— Vertical  section  of  blastoderm  of  chick  (1st  day  of  incubation).  epiblast,  consisting 
of  short  columnar  cells;  D,  hypoblast,  consisting  of  a  single  layer  of  flattened  cells;  If,  "formative 
cells.'"  They  are  seen  on  the  right  of  the  figure,  passing  in  between  the  epiblast  and  hypoblast  to 
form  the  mesoblast;  white  yelS:  granules.  Many  of  the  large  "formative  cells"  are  seen  contain- 
ing these  granules  (Strieker). 

cells,  which  migrate  by  amoeboid  movement  round  the  edge  of  the  hypo- 
blast (Fig.  408,  M),  constitute  a  third  layer  (mesoblast). 

These  important  changes  are  among  the  earliest  results  of  incubation. 

From  the  epiblast  are  ultimately  developed  the  epidermis  and  its  various 
appendages,  also  the  cerebro-spinal  nerve-centres,  the  sensorial  epithelium 
of  the  organs  of  special  sense  (eye,  ear,  nose),  and  the  epithelium  of  the 
mouth  and  salivary  glands. 

From  the  hypoblast  is  developed  the  epithelium  of  the  whole  digestive 
canal,  together  with  that  lining  the  ducts  of  all  the  glands  which  open  into 
it;  also  the  glandular  parenchyma  of  the  glands  {e.g.,  liver  and  pancreas) 
connected  with  it,  and  the  epithelium  of  the  respiratory  track. 

From  the  mesoblast  are  derived  all  the  tissues  and  organs  of  the  body 
intervening  between  these  two,  the  whole  group  of  the  connective  tissues. 


256  HA]S^D-BOOK  OF  PHYSIOLOGY. 

the  muscles  and  the  cerebro-spiual  and  sympathetic  nerves,  with  the  vas- 
cular and  genito-urinary  systems,  and  all  the  digestive  canal  with  its 
various  appendages  with  the  exception  of  the  lining  epithelium  above 
mentioned. 

First  Rudimej^ts  of  the  Embryo  and  its  Chief  Organ's 

Germinal  Area. — The  position  in  which  the  embryo  is  about  to  appear 
is  early  marked  out  by  a  central  roundish  opacity  in  the  blastoderm,  due 
to  the  accumulation  of  cells  in  this  region.  This  germinal  area,  which  is 
at  first  circular,  changes  its  shape,  becoming  pyriform,  and  finally  an 
elongated  oval  constricted  in  the  middle  like  a  savoy  biscuit. 

The  central  portion  becomes  transparent, 
and  thus  we  have  an  area  pellitcida,  sur- 
rounded by  an  area  opaca  (Fig.  409). 

Primitive  Groove. — The  first  trace  of 
the  embryo  is  a  shallow  longitudinal  groove 
(primitive  groove),  which  appears  toward  the 
posterior  part  of  the  area  pellucida  (Figs. 
409,  412). 

Medullary   Groove. — The  primitive 
groove  is  but  transitory,  and  is  soon  dis- 
placed by  the  medullary  groove,  which  first  ap- 
pears at  the  anterior  extremity  of  the  future 
embryo,  and  grows  backward,  gradually  caus- 
ing the  disappearance  of  the  primitive  groove. 
Laminae  dorsales. — The  medullary  canal  is  bounded  by  two  longitu- 
dinal elevations  {lamincB  dorsales),  which  are  folds  consisting  entirely  of 
cells  of  the  epiblast:  these  grow  up  and  arch  over  the  medullary  groove 


Fig.  410.— Transverse  section  through  embryo  chick  (26  hours),   a,  epiblast;  6.  mesoblast;  c,  hy- 

Soblast;  rf,  central  portion  of  mesoblast,  which  is  here  fused  with  epiblast;  e,  primitive  groove;  /, 
orsal  ridge  (Klein). 

(Fig.  411)  till  they  coalesce  in  the  middle  line,  converting  it  from  an  open 
furrow  into  a  closed  tube — the  primitive  cerebro-spinal  axis.  Over  this 
closed  tube,  the  walls  of  which  consist  of  more  or  less  cylindrical  cells,  the 
superficial  layer  of  the  epiblast  is  now  continued  as  a  distinct  membrane. 


Fig.  409.— Impregnated  egg,  with 
commencement  of  formation  of  em- 
bryo :  showing  the  area  germinativa 
or  embryonic  spot,  the  area  peUu- 
cida,  and  the  primitive  groove  or 
trace  (Dalton). 


GENERATION  AND  DEVELOPMENT.  257 

The  union  of  the  medullary  folds  or  laminae  dorsales  takes  place  first 
about  the  neck  of  the  future  embryo;  they  soon  after  unite  over  the  region 
of  the  head,  while  the  closing  in  of  the  groove  progresses  much  more 

m  fo 


Fig.  411. — Diagram  of  transverse  section  through  an  embryo  before  the  closing-in  of  the  medul- 
lary groove,   m,  cells  of  epiblast  lining  the  medullary  groove  which  will  form  the  spinal  cord; 
epiblast;  d,  hypoblast;  ch,  notochord;  it,  proto vertebra;  sp,  mesoblast;  w,  edge  of  lamina  dorsaUs, 
folding  over  medullary  groove.  (Kolliker.) 

slowly  toward  the  hinder  extremity  of  the  embryo.  The  medullary  groove 
is  by  no  means  of  uniform  diameter  throughout,  but  even  before  the  dorsal 
laminae  have  united  over  it,  is  seen  to  be  dilated  at  the  anterior  extremity 
and  obscurely  divided  by  constrictions  into  the  three  primary  vesicles  of 
the  brain. 


Fig.  412.— Portion  of  the  germinal  membrane,  with  rudiments  of  the  embryo;  from  the  oroxa.  of 
a  bitch.  The  primitive  groove,  a,  is  not  yet  closed,  and  at  its  upper  or  cephaUc  end  presents  three 
dilatations,  b,  which  correspond  to  the  three  divisions  or  vesicles  of  the  brain.  At  its  lower  extremity 
the  groove  presents  a  lancet-shaped  dilatation  (sinus  rhomboidalis)  c.  The  margins  of  the  groove 
consist  of  clear  pellucid  nerve-substance.  Along  the  bottom  of  the  groove  is  observed  a  faint  streaky 
which  is  probably  the  chorda  dorsalis.   d,  Vertebral  plates.  (BischofE.) 

The  part  from  which  the  spinal  cord  is  formed  is  of  nearly  uniform 
calibre,  while  toward  the  posterior  extremity  is  a  lozenge-shaped  dilata- 
tion, which  is  the  last  part  to  close  in  (Fig.  412). 

Notochord. — At  the  same  time  there  appears  in  the  middle  line,  im- 
mediately beneath  the  floor  of  the  medullary  groove,  a  rod-shaped  structure- 
formed  by  an  aggregation  of  cells  of  the  mesoblast;  it  soon  becomes  quite 
distinct  from  the  remainder  of  the  mesoblast,  and  constitutes  an  axial  cord 
Vol.  II.— 17. 


258 


HAND-BOOK  OF  PHYSIOLOGY. 


(notochord,  cliorda  dorsalis)  (ch,  Fig.  414)  which  extends  nearly  the  whole 
length  of  the  medullary  canal,  terminating  anteriorly  beneath  the  middle 
one  of  the  three  cerebral  vesicles,  and  occupies  the  future  position  of  the 
bodies  of  the  vertebrae  and  basis  cranii. 

Protovertebrae. — Simultaneously  on  each  side  of  the  notochord 
appears  a  longitudinal  thickening  of  the  mesoblast. 

Thus  we  have  two  lateral  plates  which  when  viewed  from  above  are  seen 
to  be  divided  into  a  number  of  squarish  segments  (protovertehrce)  by  the 


3FB  C% 


Fig.  413.— Embryo  chick  (36  hours),  viewed  from  beneath  as  a  transparent  object  (magnified). 
pZ,  outline  of  pellucid  area;  FB^  fore-brain,  or  first  cerebral  vesicle:  from  its  sides  project  ou,  the 
optic  vesicles;  SO,  backward  limit  of  somatopleure  fold,  "tucked  in"  under  head;  a,  headfold  or  true 
amnion;  a',  reflected  layer  of  amnion,  sometimes  termed  "false  amnion";  sp^  backward  limit  of 
splanchnoplem-e  folds,  along  which  rim  the  omphalomesaraic  veins  uniting  to  form  /i,  the  heart, 
which  is  continued  forward  into  6a,  the  bulbus  arteriosus;  d,  the  fore-gut,  l>ing  behind  the  heart, 
and  having  a  wide  crescentic  opening  between  the  splanchnopleure  folds;  HB^  hind-brain;  MB^  mid- 
brain; pv,  protovertebree  lying  behind  the  fore-gut;  mc,  line  of  junction  of  medullary  folds  and  of 
notochord;  eft,  front  end  of  notochord;  vpZ,  vertebral  plates;  pr,  the  primitive  groove  at  its  caudal 
end.  (Foster  and  Balfom-.) 

formation  of  transverse  clefts.  The  first  three  or  four  of  these  protoverte- 
brae  make  their  appearance  in  the  cervical  region,  while  one  or  two  more 
are  formed  in  front  of  tliis  point:  and  the  series  is  continued  backward 
till  the  whole  medullary  canal  is  flanked  by  them  (Fig.  413). 

Splitting  of  the  Mesoblast. — External  to  the  protovertebrse,  the 
mesoblast  now  splits  into  two  laminae  {parietal  and  visceral):  of  these  tlie 
former,  when  traced  out  from  tlie  central  axis,  is  seen  to  be  in  close  appo- 
sition with  the  e})iblast  and  gives  origin  to  the  parietes  of  the  trunk,  while 


GENERATION  AND  DEVELOPMENT. 


259 


the  latter  adheres  more  or  less  closely  to  the  hypoblast,  and  gives  rise  to 
the  serous  and  muscular  walls  of  the  alimentary  canal  and  several  other 
parts  (Fig.  414). 

The  united  parietal  layer  of  the  mesoblast  with  the  epiblast  is  termed 
Somatopleure,  the  united  visceral  layer  and  hypoblast,  Splanchnopleure. 


Fig.  414.— Transverse  section  through  dorsal  region  of  embryo  chick  (45  hours).  One  half  of  the 
section  is  represented:  if  completed  it  would  extend  as  far  to  the  left  as  to  the  right  of  the  line  of  the 
medullary  canal  {Mc).  ^,  epiblast;  C,  hypoblast,  consisting  of  a  single  layer  of  flattened  cells;  Mc, 
medullary  canal;  Pv,  protovertebrae;  PTd,  Wolffian  duct;  So,  somatopleure;  Sp,  splanchnoplem-e; 
pp,  pleiu-o-peritoneal  cavity;  c/i,  notochord;  ao,  dorsal  aorta,  containing  blood-cells;  v,  blood-vessels 
of  the  yolk-sac.   (Foster  and  Balfour.) 

The  space  between  them  is  the  pleuro-peritoneal  cavity,  which  becomes 
subdivided  by  subsequent  partitions  into  pericardium,  pleura,  and  peri- 
toneum. 

Head  and  Tail  Folds.  Body  Cavity. — Every  vertebrate  animal 
consist  essentially  of  a  longitudinal  axis  (vertebral  column)  with  a  neural 
canal  above  it,  and  a  body-cavity  (containing  the  alimentary  canal)  beneath. 

We  have  seen  how  the  earliest  rudiments  of  the  central  axis  and  the 
neural  canal  are  formed;  we  must  now  consider  how  the  general  body- 
cavity  is  developed.  In  the  earliest  stages  the  embryo  lies  flat  on  the  sur- 
face of  the  yelk,  and  is  not  clearly  marked  off  from  the  rest  of  the  blas- 
toderm: but  gradually  a  crescentic  depression,  (with  its  concavity  backward) 
is  formed  in  the  blastoderm,  limiting  the  head  of  the  embryo;  the 
blastoderm  is,  as  it  were,  tucked  in  under  the  head,  which  thus  comes  to 
project  above  the  general  surface  of  the  membrane:  a  similar  tucking  in 
of  blastoderm  takes  place  at  the  caudal  extremity,  and  thus  the  head  and 
tail  folds  are  formed  (Fig.  415). 

Similar  depressions  mark  off  the  embryo  laterally,  until  it  is  completely 
surrounded  by  a  sort  of  moat  which  it  overhangs  on  all  sides,  and  which 
clearly  defines  it  from  the  yelk. 

This  moat  runs  in  further  and  further  all  round  beneath  the  over- 
hanging embryo,  till  the  latter  comes  to  resemble  a  canoe  turned  upside- 
down,  the  ends  and  middle  being,  as  it  were,  decked  in  by  the  folding  or 
tucking  in  of  the  blastoderm,  while  on  the  ventral  surface  there  is  still  a 
large  communication  with  the  yelk,  corresponding  to  the  "welF'  or  un- 
decked portion  of  the  canoe. 


260 


HAND-BOOK  OF  PHYSIOLOGY. 


This  communication  between  the  embryo  and  the  yelk  is  gradually 
contracted  by  the  further  tucking  in  of  the  blastoderm  from  all  sides. 


Fig.  415.— Diagrammatic  longitudinal  section  through  the  axis  of  an  embryo.  The  head-fold  has 
commenced,  but  the  tail-fold  has  not  yet  appeared.  FSo,  fold  of  the  somatopleure;  FSp,  fold  of  the 
splanchnopleure;  the  line  of  reference,  FSo,  lies  outside  the  embryo  in  the  "moat,''  which  marks  off 
the  overhanging  head  from  the  amnion;  D,  inside  the  embryo,  is  that  part  which  is  to  become  the 
fore-gut;  FSo  and  FSp,  are  both  parts  of  the  head-fold,  and  travel  to  the  left  of  the  figure  as  develop- 
ment proceeds;  pp,  space  between  somatopleure  and  splanchnopleiu-e,  pleuro-peritoneal  cavity;  Am. 
commencing  head-fold  of  amnion;  iVC,  neiu-al  canal;  C/i,  notochord;  Ht,  heart;  A,  B,  C\  epiblast, 
mesoblast,  hypoblast.   (Foster  and  Balfom-.) 

till  it  become  narrowed  down,  as  by  an  invisible  constricting  band,  to  a 
mere  pedicle  which  passes  out  of  the  body  of  the  embryo  at  the  point  of 
the  future  umbilicus. 


Fig.  416.— Diagrammatic  section  showing  the  relation  in  a  manunal  between  the  primitive  alimen 
tary  canal  and  the  membranes  of  the  oviun.  The  stage  represented  in  tliis  diagrani  corresponds  t<y 
that  of  the  fifteentli  or  seventt^enth  day  in  the  human  enibrj^o,  previous  to  the  expansion  or  the  al- 
lantois;  c,  the  villous  chorion;  a,  the  anuiion;  a',  the  place  of  convergence  of  tlu>  amnion  and  reflex- 
ion of  the  false  amnit)n  a"  a'\  or  outer  or  corneus  layer;  <?,  the  head  and  trunk  of  the  embryo,  com- 
prising the  primitive  vertebra*  and  c(>rebro-spinal  axis;  /,  /,  the  sinipU>  alimentary  canal  in  its  upper 
and  lower  portions.  Ininiediately  beneath  th«'  right  hand  /,  is  seen  the  f(i>tal  heart,  lying  in  the  an- 
terior part  of  the  i)leuro-p('rit<)n('al  cavity;  v,  t\\r  yolk-sac,  or  umbilical  vesicle;  v  /,  the  vitello-intes- 
tinal  oi)ening;  «,  the  allantois  connected  by  a  pedicle  with  the  anal  portion  of  the  alimentary  canal. 
(From  Quain's  "Anatomy.'") 


Visceral  Plates. — The  downwardly  folded  portions  of  blastoderm 
are  termed  the  visceral  platei>. 


GENERATION  AND  DEVELOPMENT. 


261 


Thus  we  see  that  the  body-cavity  is  formed  by  the  downward  folding 
of  the  visceral  plates,  just  as  the  neural  cavity  is  produced  by  the  upward 
growth  of  the  dorsal  laminae,  the  difference  being  that,  in  the  visceral  or 
ventral  laminae,  all  three  layers  of  the  blastoderm  are  concerned. 

The  folding  in  of  the  splanchnopleure,  lined  by  hypoblast,  pinches 
off,  as  it  were,  a  portion  of  the  yelk-sac,  enclosing  it  in  the  body-cavity. 
This  forms  the  rudiment  of  the  alimentary  canal,  which  at  this  period 
ends  blindly  toward  the  head  and  tail,  while  in  the  centre  it  communicates 
freely  with  the  cavity  of  the  yelk-sac  through  the  canal  termed  vitelline 
or  omplialo-mesenteric  duct. 

The  yelk-sac  thus  becomes  divided  into  two  portions  which  communi- 
cate through  the  vitelline  duct,  that  portion  within  the  body  giving  rise, 
as  above  stated,  to  the  digestive  canal,  and  that  outside  the  body  remain- 
ing for  some  time  as  th.^  umbilical  vesicle  (Fig.  417,  ys).  The  hypoblast 
forming  the  epithelium  of  the  intestine  is  of  course  continuous  with  the 
lining  membrane  of  the  umbilical  vesicle,  while  the  visceral  plate  of  the 
mesoblast  is  continuous  with  the  outer  layer  of  the  umbilical  vesicle. 

All  the  above  details  will  be  clear  on  reference  to  the  accompanying 
diagrams. 

FCETAL  MeMBEAE^ES. 

Umbilical  Vesicle  or  Yelk-sac. — The  splanchnopleure,  lined  by 
hypoblast,  forms  the  yelk-sac  in  Eeptiles,  Birds,  and  Mammals;  but  in 
Amphibia  and  Fishes,  since  there  is  neither  am?iion  nor  allantois,  the 
wall  of  the  yelk-sac  consists  of  all  three  layers  of  the  blastoderm,  enclosed, 
of  course,  by  the  original  vitelline  membrane. 


Fig.  417. — Diagrams,  showing  three  successive  stages  of  development.  Transverse  vertical  sec- 
tions. The  yelk-sac,  ys,  is  seen  progressively  diminishing  in  size.  In  the  embryo  itself  the  medul- 
lary canal  and  notochord  are  seen  in  section,  a',  in  middle  figure,  the  alimentary  canal,  becoming 
pinched  off,  as  it  were,  from  the  yelk-sac;  a',  in  right  hand  figure,  alimentary  canal  completely 
closed;  a,  in  last  two  figures,  amnion;  ac,  cavity  of  amnion  filled  with  amniotic  fluid;  pp,  space  be- 
tween amnion  and  chorion,  continuous  with  the  pleuro-peritoneal  cavity  inside  the  body ;  vt,  vitel- 
line membrane;  ys^  yelk-sac,  or  umbiUcal  vesicle.   (Foster  and  Balfour.) 

The  body  of  the  embryo  becomes  in  great  measure  detached  from  the 
yelk-sac  or  umbilical  vesicle,  which  contains,  however,  the  greater  part 
of  the  substance  of  the  yelk,  and  furnishes  a  source  whence  nutriment  is 
derived  for  the  embryo.    This  nutriment  is  absorbed  by  the  numerous 


262 


HAND-BOOK  OF  PHYSIOLOGY. 


vessels  (omphalo-mesenteric)  which  ramify  in  the  walls  of  the  yelk-sac, 
forming  what  in  birds  is  termed  the  m^ea  vascnlosa.  In  Birds,  the  con- 
tents of  the  yelk-sac  afford  nourishment  until  the  end  of  incubation,  and 
the  omphalo-mesenteric  vessels  are  developed  to  a  corresponding  degree; 
but  in  Mammalia  the  office  of  the  umbilical  vesicle  ceases  at  a  very  early 
period,  the  quantity  of  the  yelk  is  small,  and  the  embryo  soon  becomes 
independent  of  it  by  the  connections  it  forms  with  the  parent.  Moreover, 
in  Birds,  as  the  sac  is  emptied,  it  is  gradually  drawn  into  the  abdomen 
through  the  umbilical  opening,  which  then  closes  over  it:  but  in  Mam- 


FiG.  418.— Diagram  showing  vascular  area  in  the  chick,  a,  area  pellucida;  6,  area  vasculosa;  c, 
area  viteUina. 

Fig.  419.— Human  embryo  of  fifth  week  with  umbilical  vesicle;  about  natural  size  (Dalton).  The 
human  umbilical  vesicle  never  exceeds  the  size  of  a  small  pea. 


malia  it  always  remains  on  the  outside;  and  as  it  is  emptied  it  contracts 
(Fig.  419),  shrivels  up,  and  together  with  the  part  of  its  duct  external  to 
the  abdomen,  is  detached  and  disappears  either  before  or  at  the  termination 
of  intra-uterine  life,  the  period  of  its  disappearance  varying  in  different 
orders  of  Mammalia. 

When  blood-vessels  begin  to  be  developed,  they  ramify  largely  over  the 
walls  of  the  umbilical  vesicle,  and  are  actively  concerned  in  absorbing  its 
contents  and  conveying  them  away  for  the  nutrition  of  the  embryo. 

The  Amnion  and  AUantois. — At  an  early  stage  of  development  of 
the  foetus,  and  some  time  before  the  completion  of  the  changes  which 
have  been  just  described,  two  important  structures,  called  respectively 
the  amnion  and  the  allantois,  begin  to  be  formed. 

Amnion. — The  amnion  is  produced  as  follows: — Beyond  the  head  and 
tail-folds  before  described  (p.  259,  Vol.  II.),  the  somatopleure  coated  by 
epiblast,  is  raised  into  folds,  which  grow  up,  arching  over  the  embryo, 
not  only  anteriorly  and  posteriorly  but  also  laterally,  and  all  converg- 
ing toward  one  ])()int  over  its  dorsal  surface  (Fig.  417).  The  growing 
up  of  these  folds  from  all  sides  and  their  convergence  toward  one  point 
very  closely  resembles  the  folding  inward  of  the  visceral  plates  already 
described,  and  hence,  by  some,  the  ])oint  at  which  the  amniotic  folds 
meet  over  the  back  has  been  termed  the  "amniotic  umbilicus. 


Fig.  418. 


Fig.  419. 


GENERATION  AND  DEVELOPMENT. 


263 


The  folds  not  only  come  into  contact  but  coalesce.  The  inner  of  the 
two  layers  forms  the  true  amnion,  while  the  outer  or  reflected  layer,  some- 
times termed  the  false  a7nnion,  coalesces  with  the  inner  surface  of  the 
original  vitelline  membrane  to  form  the  chorion.  This  growth  of  the 
amniotic  folds  must  of  course  be  clearly  distinguished  from  the  very 
similar  process,  already  described,  by  which  the  walls  of  the  neural  canal 
are  formed  at  a  much  earlier  stage. 

Amniotic  Cavity. — The  cavity  between  the  true  amnion  and  the  ex- 
ternal surface  of  the  embryo  becomes  a  closed  space,  termed  the  a^nniotic 
cavity  (ac,  Fig.  417). 

At  first,  the  amnion  closely  invests  the  embryo,  but  it  becomes  grad- 
ually distended  with  fluid  (liquor  amnii),  which,  as  pregnancy  advances, 
reaches  a  considerable  quantity. 

This  fluid  consists  of  water  containing  small  quantities  of  albumen 
and  urea.  Its  chief  function  during  gestation  appears  to  be  the  mechani- 
cal one  of  affording  equal  support  to  the  embryo  on  all  sides,  and  of  pro- 
tecting it  as  far  as  possible  from  the  effects  of  blows  and  other  injuries  to 
the  abdomen  of  the  mother. 

The  embryo  up  to  the  end  of  pregnancy  is  thus  immersed  in  fluid, 
which  during  parturition  serves  the  important  purpose  of  gradually  and 
evenly  dilating  the  neck  of  the  uterus  to  allow  of  the  passage  of  the 
foetus:  when  this  is  accomplished  the  amniotic  sac  bursts  and  the 
^'waters"  escape. 

On  referring  to  the  diagrams  (Fig.  417),  it  will  be  obvious  that  the 
cavity  outside  the  amnion  (between  it  and  the  false  amnion)  is  continu- 
ous with  the  pleuro-peritoneal  cavity  at  the  umbilicus.  This  cavity  is 
•not  entirely  obliterated  even  at  birth,  and  contains  a  small  quantity  of 
fluid  ("false  waters"),  which  is  discharged  during  parturition  either  be- 
fore, or  at  the  same  time,  as  the  amniotic  fluid. 

AUa7itois. — Into  the  pleuro-peritoneal  space  the  allantois  sprouts  out, 
its  formation  commencing  during  the  development  of  the  amnion. 

Growing  out  from  or  near  the  hinder  portion  of  the  intestinal  canal 
{c,  Fig.  420),  with  which  it  communicates,  the  allantois  is  at  flrst  a  solid 
pear-shaped  mass  of  splanchnopleure;  but  becoming  vesicular  by  the  pro- 
jection into  it  of  a  hollow  outgrowth  of  hypoblast,  and  very  soon  simply 
membranous  and  vascular,  it  insinuates  itself  between  the  amniotic  folds, 
just  described,  and  comes  into  close  contact  and  union  with  the  outer  of 
the  two  folds,  which  has  itself,  as  before  said,  become  one  with  the  ex- 
ternal investing  membrane  of  the  egg.  As  it  grows,  the  allantois  devel- 
opes  muscular  tissue  in  its  external  wall  and  becomes  exceedingly  vascu- 
lar; in  birds  (Fig.  421)  it  envelopes  the  whole  embryo — taking  up  vessels, 
so  to  speak,  to  the  outer  investing  membrane  of  the  egg,  and  lining  the 
inner  surface  of  the  shell  with  a  vascular  membrane,  by  these  means 
affording  an  extensive  surface  in  which  the  blood  may  be  aerated.    In  the 


264 


HAND-BOOK  OF  PHYSIOLOGY. 


human  subject  and  in  other  Mammalia,  the  vessels  carried  out  by  the 
allantois  are  distributed  only  to  a  special  part  of  the  outer  membrane  or 
cliorion,  where,  by  interlacement  with  the  vascular  system  oi  the  mother, 
a  structure  called  the  placenta  is  developed. 

In  Mammalia,  as  the  visceral  laminae  close  in  the  abdominal  cavity, 
the  allantois  is  thereby  divided  at  the  umbilicus  into  two  portions;  the 
outer  part,  extending  from  the  umbilicus  to  the  chorion,  soon  shriveling; 
while  the  inner  part,  remaining  in  the  abdomen,  is  in  part  converted 
into  the  urinary  bladder;  the  portion  of  the  inner  part  not  so  converted, 
extending  from  the  bladder  to  the  umbilicus,  under  the  name  of  the 


Fig.  420.  Fig.  421. 

Fig.  420.— Diagram  of  fecundated  egg.  a,  mnbilical  vesicle;  6,  ammotic  cavity;  c,  allantois. 
(Dalton.) 

Fig.  421.— Fecundated  egg  with  allantois  nearly  complete,  a,  inner  layer  of  amniotic  fold;  6, 
outer  layer  of  ditto;  c,  point  where  the  amniotic  folds  come  in  contact.  The  allantois  is  seen  pene- 
trating between  the  outer  and  inner  layers  of  the  amniotic  folds.  This  figure,  which  represents  only 
the  amniotic  folds  and  the  parts  within  them,  should  be  compared  with  Figs.  417, 423,  in  which  will  be 
found  the  structures  external  to  these  folds.  (Dalton.) 

urachus.  After  birth  the  umbilical  cord,  and  with  it  the  external  and 
shriveled  portion  of  the  allantois,  are  cast  off  at  the  umbilicus,  while  the 
urachus  remains  as  an  impervious  cord  stretched  from  the  top  of  the* 
urinary  bladder  to  the  umbilicus,  in  the  middle  line  of  the  ^ody,  imme- 
diately beneath  the  parietal  layer  of  the  peritoneum.  It  is  sometimes 
enumerated  among  the  ligaments  of  tjie  bladder. 

It  must  not  be  supposed  that  the  phenomena  which  have  been  succes- 
sively described,  occur  in  any  regular  order  one  after  another.  On  the 
contrary,  the  development  of  one  part  is  going  on  side  by  side  with  that 
of  another. 

The  Chorion. — It  has  been  already  remarked  that  the  allantois  is  a 
structure  which  extends  from  the  body  of  the  fostus  to  the  outer  invest- 
ing membrane  of  the  ovum,  that  it  insinuates  itself  between  the  two  layers 
of  the  amniotic  fold,  and  becomes  fused  with  the  outer  layer,  Avhich  has 
itself  become  previously  fused  with  the  vitelline  membrane.  By  these 
means  the  external  investing  membrane  of  the  ovum,  or  the  chorion,  as  it 
is  now  called,  i-ei)resents  three  layers,  namely,  the  original  vitelline  mem- 
brane, the  outer  layer  of  the  amniotic  fold,  and  the  allantois. 

Very  soon  after  the  entrance  of  the  ovum  into  the  uterus,  in  the 
human  subject,  the  outer  surface  of  the  chorion  is  found  beset  with  fine 


GENERATION  AND  DEVELOPMENT. 


265 


processes,  the  so-called  villi  of  the  chorion  (Figs.  422,  423),  which  give 
it  a  rough  and  shaggy  appearance.  At  first  only  cellular  in  structure, 
these  little  outgrowths  subsequently  become  vascular  by  the  development 
in  them  of  loops  of  capillaries  (Fig.  423);  and  the  latter  at  length  form 
the  minute  extremities  of  the  blood-vessels  which  are,  so  to  speak,  con- 


FiGS,  422  and  423  (after  Todd  and  Bowman),  a,  chorion  with  villi.  The  villi  are  shown  to  be  best 
developed  in  the  part  of  the  chorion  to  which  the  allantois  is  extending;  this  portion  ultimately  be- 
comes the  placenta;  6,  space  between  the  two  layers  of  the  amnion;  c,  amniotic  cavity;  cZ,  situation 
of  the  intestine,  showing  its  connection  with  the  umbiUcal  vesicle;  e,  umbilical  vesicle;  /,  situation 
of  the  heart  and  vessels;  gr,  allantois. 

ducted  from  the  foetus  to  the  chorion  by  the  allantois.  The  function  of 
the  villi  of  the  chorion  is  evidently  the  absorption  of  nutrient  matter  for 
the  foetus;  and  this  is  probably  supplied  to  them  at  first  from  the  fluid 
matter,  secreted  by  the  follicular  glands  of  the  uterus,  in  which  they  are 
soaked.  Soon,  however,  the  foetal  vessels  of  the  villi  come  into  more 
intimate  relation  with  the  vessels  of  the  uterus.  The  part  at  which  this 
relation  between  the  vessels  of  the  foetus  and  those  of  the  parent  ensues, 


Fig.  424. 


is  not,  however,  over  the  whole  surface  of  the  chorion :  for,  although  all 
the  villi  become  vascular,  yet  they  become  indistinct  or  disappear  except 
at  one  part,  where  they  are  greatly  developed,  and  by  their  branching  give 
rise,  with  the  vessels  of  the  uterus,  to  the  formation  of  the  placenta. 


266 


HAND-BOOK  OF  PHYSIOLOGY. 


To  understand  the  manner  in  which  the  fcetal  and  maternal  blood- 
vessels come  into  relation  with  each  other  in  the  placenta,  it  is  necessary 
briefly  to  notice  the  changes  which  the  uterus  undergoes  after  impregna- 
tion. These  changes  consist  especially  of  alterations  in  structure  of  the 
superficial  part  of  the  mucous  membrane  which  lines  the  interior  of  the 
uterus,  and  which  forms,  after  a  kind  of  development  to  be  immediately 
described,  the  memlrana  decidua,  so  called  on  account  of  its  being  dis- 
charged from  the  uterus  at  birth. 

FORMATIOIT  OF  THE  PlACEKTA. 

The  mucous  membrane  of  the  human  uterus,  which  consists  of  a 
matrix  of  connective  tissue  containing  numerous  corpuscles  (adenoid 
tissue),  and  is  lined  internally  by  columnar  ciliated  epithelium,  is  abun- 


Fi&,  425.— Section  of  the  lining  membrane  of  a  human  uterus  at  the  period  of  commencing  preg- 
nancy, showing  the  arrangement  and  other  peculiarities  of  the  glands,  d,  d,  d,  with  their  orifices, 
a,  a,  a,  on  the  internal  surface  of  the  organ.   Twice  the  natural  size. 

dantly  beset  with  tubular  glands,  arranged  perpendicularly  to  the  surface 
(Fig.  425).  These  follicles  are  very  small  in  the  unimpregnated  uterus; 
but  when  examined  shortlv  after  imnregnation,  they  are  found  elongated. 


B 


Fig.  426. — Two  thin  segments  of  human  decidua  after  recent  Impregnation,  viewed  on  a  dark 
ground;  they  show  the  openings  on  the  surface  of  the  membrane,  a  is  magnified  six  diameters,  and 
B  twelve  diameters.  At  1,  the  lining  of  epithelium  is  seen  within  the  orifices,  at  2  it  has  escaped. 
(Sharpey.) 

enlarged,  and  mucli  waved  and  contorted  toward  their  deep  and  closed 
extremity,  which  is  implanted  at  some  dcptli  in  the  tissue  of  tlie  uterus, 
and  may  dilate  into  two  or  three  closed  sacculi  (Fig.  425). 


GENERATION  AND  DEVELOPMENT. 


267 


The  glands  are  lined  by  columnar  ciliated  epithelium,  and  they  open 
on  the  inner  surface  of  the  mucous  membrane  by  small  round  orifices  set 
closely  together  [a,  a,  Fig.  426). 

On  the  internal  surface  of  the  mucous  membrane  may  be  seen  the  cir- 
cular orifices  of  the  glands,  many  of  which  are,  in  the  early  period  of 
pregnancy,  surrounded  by  a  whitish  ring,  formed  of  the  epithelium  which 
lines  the  follicles  (Fig.  426). 

Membrana  decidua. — Coincidently  with  the  occurrence  of  preg- 
nancy, important  changes  occur  in  the  structure  of  the  mucous  membrane 


Fig.  427.— Diagrammatic  view  of  a  vertical  transverse  section  of  the  uterus  at  the  seventh  or 
eighth  week  of  pregnancy,  c,  c,  c',  cavity  of  uterus,  which  becomes  the  cavity  of  the  decidua,  open- 
ing at  c,  c,  the  cornua,  into  the  Fallopian  tubes,  and  at  c'  into  the  cavity  of  the  cervix,  which  is 
closed  by  a  plug  of  mucus;  d  v,  decidua  vera;  d  r,  decidua  reflexa,  with  the  sparser  vilh  imbedded  in 
its  substance ;  d  s,  decidua  serotina,  involving  the  more  developed  chorionic  viUi  of  the  commencing 
placenta.  The  foetus  is  seen  lying  in  the  amniotic  sac;  passing  up  from  the  ujnbilicus  is  seen  the 
umbilical  cord  and  its  vessels,  passing  to  their  distribution  in  the  viUi  of  the  chorion ;  also  the  pedicle 
of  the  yelk-sac,  which  lies  in  the  cavity  between  the  amnion  and  chorion.   (Allen  Thomson.) 

of  the  uterus.  The  epithelium  and  sub-epithelial  connective  tissue,  to- 
gether with  the  tubular  glands,  increase  rapidly,  and  there  is  a  greatly 
increased  vascularity  of  the  whole  mucous  membrane,  the  vessels  of  the 
mucous  membrane  becoming  larger  and  more  numerous;  while  a  sub- 
stance composed  chiefly  of  nucleated  cells  fills  up  the  interfollicular  spaces 
in  which  the  blood-vessels  are  contained.  The  effect  of  these  changes  is 
an  increased  thickness,  softness,  and  vascularity  of  the  mucous  mem- 
brane, the  superficial  part  of  which  itself  forms  the  memhrana  decidua. 


268 


HAND-BOOK  OF  PHYSIOLOGY. 


The  object  of  this  increased  development  seems  to  be  the  production 
of  nutritive  materials  for  the  ovum;  for  the  cavity  of  the  uterus  shortly 
becomes  filled  with  secreted  fluids  consisting  almost  entirely  of  nucleated 
cells  in  which  the  villi  of  the  chorion  are  imbedded. 

When  the  ovum  first  enters  the  uterus  it  becomes  imbedded  in  the 
structure  of  the  decidua,  which  is  yet  quite  soft,  and  in  which  soon  after- 
ward three  portions  are  distinguishable.  These  have  been  named  the 
decidua  vera,  the  decidua  reflexa,  and  the  decidua  serotina.  The  first  of 
these,  the  decidua  vera,  lines  the  cavity  of  the  uterus;  the  second,  or 
decidua  reflexa,  is  a  part  of  the  decidua  vera  which  grows  up  around  the 
ovum,  and,  wrapping  it  closely,  forms  its  immediate  investment. 

The  third,  or  decidua  serotina,  is  the  part  of  the  decidua  vera  which 
becomes  especially  developed  in  connection  with  those  villi  of  the  chorion 
which,  instead  of  disappearing,  remain  to  form  the  foetal  part  of  the 
jplacenta. 

In  connection  with  these  villous  processes  of  the  chorion,  there  are 
developed  depressio?is  or  crypts  in  the  decidual  mucous  membrane,  which 
correspond  in  shape  with  the  villi  they  are  to  lodge;  and  thus  the  chori- 
onic villi  become  more  or  less  imbedded  in  the  maternal  structures.  These 
uterine  crypts,  it  is  important  to  note,  are  not,  as  was  once  supposed, 
merely  the  open  mouths  of  the  uterine  follicles  (Turner). 

As  the  ovum  increases  in  size,  the  decidua  vera  and  the  decidua  reflexa 
gradually  come  into  contact,  and  in  the  third  month  of  pregnancy  the 
cavity  between  them  has  quite  disappeared.  Henceforth  it  is  very  diffi- 
cult, or  even  impossible,  to  distinguish  the  two  layers. 

The  Placenta. — During  these  changes  the  deeper  part  of  the  mucous 
membrane  of  the  uterus,  at  and  near  the  region  where  the  placenta  is 
placed,  becomes  hollowed  out  by  sinuses,  or  cavernous  spaces,  which  com- 
municate on  the  one  hand  with  arteries  and  on  the  other  with  veins  of 
the  uterus.  Into  these  sinuses  the  villi  of  the  chorion  protrude,  pushing 
the  thin  wall  of  the  sinus  before  them,  and  so  come  into  intimate  relation 
with  the  blood  contained  in  them.  There  is  no  direct  communication 
between  the  blood-vessels  of  the  mother  and  those  of  the  foetus;  but  the 
layer  or  layers  of  membrane  intervening  between  the  blood  of  the  one  and 
of  the  other  offer  no  obstacle  to  a  free  interchange  of  matters  between 
them.  Thus  the  villi  of  the  chorion  containing  foetal  blood,  are  bathed 
or  soaked  in  maternal  blood  contained  in  the  uterine  sinuses.  The 
arrangement  may  be  roughly  compared  to  filling  a  glove  with  fa^tal 
blood,  and  dipping  its  fingers  into  a  vessel  containing  maternal  blood. 
But  in  the  f(x^tal  villi  there  is  a  constant  stream  of  blood  into  and  out  of 
tlie  loop  of  capillary  blood-vessels  contained  in  it,  as  there  is  also  into  and 
out  of  the  maternal  sinuses. 

It  would  seem  from  tlie  observations  of  Goodsir,  that,  at  the  villi 
of  tlie  placental  tufts,  where  the  fa^tal  and  maternal  portions  of  the 


GENERATION  AND  BEVELOPxMENT. 


269 


placenta  are  brought  into  close  relation  with  each  other,  the  blood  in  the 
vessels  of  the  mother  is  separated  from  that  in  the  vessels  of  the  foetus 
by  the  intervention  of  two  distinct  sets  of  nucleated  cells  (Fig.  428). 
One  of  these  (b)  belongs  to  the  maternal  portion  of  the  placenta,  is  placed 
between  the  membrane  of  the  villus  and  that  of  the  vascular  system  of 
the  mother,  and  is  probably  designed  to  separate 
from  the  blood  of  the  parent  the  materials  des- 
tined for  the  blood  of  the  foetus;  the  other  (/)  be- 
longs to  the  foetal  portion  of  the  placenta,  is  sit- 
uated between  the  membrane  of  the  villus  and  the 
loop  of  vessels  contained  within,  and  probably 
serves  for  the  absorption  of  the  material  secreted 
by  the  other  sets  of  cells,  and  for  its  conveyance 
into  the  blood-vessels  of  the  foetus.  Between  the 
two  sets  of  cells  with  their  investing  membrane 
there  exists  a  space  (d),  into  which  it  is  probable 
that  the  materials  secreted  by  the  one  set  of  cells 
of  the  villus  are  poured  in  order  that  they  may  be 
absorbed  by  the  other  set,  and  thus  conveyed  into 
the  foetal  vessels. 

Not  only,  however,  is  there  a  passage  of  materials  from  the  blood  of 
the  mother  into  that  of  the  foetus,  but  there  is  a  mutual  interchange  of 
materials  between  the  blood  both  of  foetus  and  of  parent;  the  latter  sup- 
plying the  former  with  nutriment,  and  in  turn  abstracting  from  it 
materials  which  require  to  be  removed. 

Alexander  Harvey's  experiments  were  very  decisive  on  this  point. 
The  view  has  also  received  abundant  support  from  Hutchinson's  impor- 
tant observations  on  the  communication  of  syphilis  from  the  father  to 
the  mother,  through  the  instrumentality  of  the  foetus;  and  still  more 
from  Savory's  experimental  researches,  which  prove  quite  clearly  that  the 
female  parent  may  be  directly  inoculated  through  the  foetus.  Having 
opened  the  abdomen  and  uterus  of  a  pregnant  bitch,  Savory  injected  a 
solution  of  strychnia  into  the  abdominal  cavity  of  one  foetus,  and  into  the 
thoracic  cavity  of  another,  and  then  replaced  all  the  parts,  every  precau- 
tion being  taken  to  prevent  escape  of  the  poison.  In  less  than  half  an 
hour  the  bitch  died  from  tetanic  spasms:  the  foetuses  operated  on  were 
also  found  dead,  while  the  others  were  alive  and  active.  The  experi- 
ments, repeated  on  other  animals  with  like  results,  leave  no  doubt  of  the 
rapid  and  direct  transmission  of  matter  from  the  foetus  to  the  mother, 
through  the  blood  of  the  placenta. 

The  placenta,  therefore,  of  the  human  subject  is  composed  of  a  fcetal 
part  and  a  maternal  part, — the  term  placenta  properly  including  all  that 
entanglement  of  foetal  villi  and  maternal  sinuses,  by  means  of  which  the 
blood  of  the  foetus  is  enriched  and  purified  after  the  fashion  necessary 
for  the  proper  growth  and  development  of  those  parts  which  it  is  designed 
to  nourish. 


Fig.  428.— Extremity  of  a 
placental  villus  a,  lining 
membrane  of  the  vascular 
system  of  the  mother;  b,  cells 
immediately  lining  a;  d, space 
between  the  maternal  and 
foetal  portions  of  the  villus ;  e, 
internal  membrane  of  the 
villus,  or  external  membrane 
of  the  chorion;  /,  internal 
cells  of  the  villus,  or  cells  of 
the  chorion;  g,  loop  of  um- 
bilica  vessels.  (Goodsir.) 


270 


HAND-BOOK  OF  PHYSIOLOGY. 


The  importance  of  the  placenta  is  at  once  apparent  if  we  remember 
that,  during  the  greater  portion  of  intra-uterine  life,  the  maternal  blood 
circulating  in  its  vessels  supplies  the  foetus  with  both  food  and  oxygen. 
It  thus  performs  the  functions  which  in  later  life  are  discharged  by  the 
alimentary  canal  and  lungs. 

The  whole  of  this  structure  is  not,  as  might  be  imagined,  thrown  off 
immediately  after  birth.  The  greater  part,  indeed,  comes  away  at  that 
time,  as  the  after-hirtli;  and  the  separation  of  this  portion  takes  place  by 
a  rending  or  crushing  through  of  that  part  at  which  its  cohesion  is  least 
strong,  namely,  where  it  is  most  burrowed  and  undermined  by  the  cav- 
ernous spaces  before  referred  to.  In  this  way  it  is  cast  off  with  the  foetal 
membrane  and  the  decidua  vera  and  rejiexa,  together  with  a  part  of  the 
decidua  serotina.  The  remaining  portion  withers,  and  disappears  by 
being  gradually  either  absorbed,  or  thrown  off  in  the  uterine  discharges 
or  the  lochia,  which  occur  at  this  period. 

A  new  mucous  membrane  is  of  course  gradually  developed,  as  the  old 
one,  by  its  peculiar  transformation  into  what  is  called  the  decidua,  ceases 
to  perform  its  original  functions. 

The  umMUcal  cord,  which  in  the  latter  part  of  foetal  life  is  almost 
solely  composed  of  the  two  arteries  and  the  single  vein  which  respectively 
convey  foetal  blood  to  and  from  the  placenta,  contains  the  remnants  of 
other  structures  which  in  the  early  stages  of  the  development  of  the 
embryo  were,  as  already  related,  of  great  comparative  importance.  Thus, 
in  early  foetal  life,  it  is  composed  of  the  following  parts: — (1.)  Exter- 
nally, a  layer  of  the  amnion,  reflected  over  it  from  the  umbilicus.  (2.) 
The  umbilical  vesicle  with  its  duct  and  appertaining  omphalo-niesenteric 
blood-vessels.  (3.)  The  remains  of  the  allantois,  and  continuous  with 
it  the  urachus.  (4.)  The  umbilical  vessels,  which,  as  just  remarked, 
ultimately  form  the  greater  part  of  the  cord. 

DEVELOPMEifT  OF  ORGANS. 

It  remains  now  to  consider  in  succession  the  development  of  the  several 
organs  and  systems  of  organs  in  the  further  progress  of  the  embryo. 
The  accompanying  figure  (Fig.  429)  shows  the  chief  organs  of  the  body 
in  a  moderately  early  stage  of  development. 

Development  of  the  Vertebral  Column  and  Cranium. 

The  primitive  part  of  the  vertebral  column  in  all  the  Vertebrata 
is  the  chorda  dorsalis  (notochord),  which  consists  entirely  of  soft 
cellular  cartilage.  This  cord  tapers  to  a  point  at  the  cranial  and 
caudal  extremities  of  the  animal.  In  the  progress  of  its  develop- 
ment, it  is  found  to  become  enclosed  in  a  membranous  sheath,  which 


GENERATION  AND  DEVELOPMENT. 


271 


at  length  acquires  a  fibrous  structure,  composed  of  transverse  an- 
nular fibres.  The  chorda  dorsalis  is  to  be  regarded  as  the  azygos  axis 
of  the  spinal  column,  and,  in  particular,  of  the  future  bodies  of  the  ver- 
tebrae, although  it  never  itself  passes  into  the  state  of  hyaline  cartilage  or 
bone,  but  remains  enclosed  as  in  a  case  within  the  persistent  parts  of  the 
vertebral  column  which  are  developed  around  it.  It  is  permanent,  how- 
ever, only  in  a  few  animals:  in  the  majority  only  traces  of  it  persist  in 
the  adult  animal. 

In  many  Fish  no  true  vertebrae  are  developed,  and  tliere  is  every  gra- 
dation from  the  amphioxus,  in  which  the  notochord  persists  through  life 


Fig.  429.— Embryo  chick  (4th  day),  viewed  as  a  transparent  object,  lying  on  its  left  side  (magni- 
fied). C  H,  cerebral  hemispheres ;  F  B,  fore-brain  oi-  vesicle  of  third  ventricle,  with  P  n,  pineal  gland 
projecting  from  its  summit;  ilfP,  mid-brain;  C  6,  cerebellum ;  /F  F,  fourth  ventricle;  i,  lens;  chs, 
choroidal  slit;  Cen  F,  auditory  vesicle;  s  m,  superior  maxillary  process;  IF,  2F,  etc.,  first,  second, 
third,  and  fourth  visceral  folds;  F,  fifth  nerve,  sending  one  branch  (ophthalmic)  to  the  eye,  and 
another  to  the  first  visceral  arch;  F7J,  seventh  nerve,  passing  to  the  second  visceral  arch;  G  Ph, 
glosso-pharyngeal  nerve,  passing  to  the  third  visceral  arch;  P gr,  pneumogastric  nerve,  passing  to- 
ward the  fourth  visceral  arch;  iv,  investing  mass;  c  h,  notochord;  its  front  end  cannot  be  seen  in 
the  living  embryo,  and  it  does  not  end  as  shown  in  the  figure,  but  takes  a  sudden  bend  downward, 
and  then  terminates  in  a  point;  Ht,  heart  seen  through  the  waUs  of  the  chest;  MP,  muscle-plates; 
TF,  wing,  showing  commencing  differentiation  of  segments,  corresponding  to  arm,  forearm,  and 
hand;  H L,  hind-hmb,  as  yet  a  shapeless  bud,  showing  no  differentiation.  Beneath  it  is  seen  the 
curved  tail.   (Foster  and  Balfour.) 

and  there  are  no  vertebral  segments,  through  the  lampreys  in  which  there 
are  a  few  scattered  cartilaginous  segments,  and  the  sharks,  in  which  many 
of  the  vertebrae  are  partly  ossified,  to  the  bony  fishes,  such  as  the  cod  and 
herring,  in  which  the  vertebral  column  consists  of  a  number  of  distinct 
ossified  vertebrae,  with  remnants  of  the  notochord  between  them.  In 
Amphibia,  Eeptiles,  Birds,  and  Mammals,  there  are  distinct  vertebrae, 
which  are  formed  as  follows: — 

Protovertebrae. — The  protovertelrce,  which  have  been  already  men- 
tioned (p.  258, Vol.  II. 'i,  send  processes  downward  and  inward  to  surround 
the  notochord,  and  also  upward  between  the  medullary  canal  and  the 
epiblast  covering  it.    In  the  former  situation,  the  cartilaginous  bodies  of 


272 


HAND-BOOK  OF  PHYSIOLOGY. 


the  vertebrae  make  their  appearance,  in  the  latter  their  arches,  which 
enclose  the  neural  canal. 

The  vertebrae  do  not  exactly  correspond  in  their  position  with  the  pro- 
tovertebrae:  but  each  permanent  vertebra  is  developed  from  the  contigu- 
ous halves  of  two  protovertebr^.  The  original  segmentation  of  the  pro- 
tovertebrae  disappears  and  a  fresh  subdivision  occurs  in  such  a  way  that  a 
permanent  invertebral  disc  is  developed  opposite  the  centre  of  each  pro- 
tovertebra.  Meanwhile  the  protovertebr^e  split  into  a  dorsal  and  ventral 
portion.  The  former  is  termed  the  musculo-cutaneous  plate,  and  from  it 
are  developed  all  the  muscles  of  the  back  together  with  the  cutis  of  the 
dorsal  region  (the  epidermis  being  derived  from  the  epiblast).  The  ven- 
tral portions  of  the  protovertebrse,  as  we  have  already  seen,  give  rise  to 
the  vertebrae  and  heads  of  the  ribs,  but  the  outer  j)art  of  each  also  gives 
rise  to  a  spinal  ganglion  and  nerve-root. 

The  chorda  is  now  enclosed  in  a  case,  formed  by  the  bodies  of  the 
vertebrae,  but  it  gradually  wastes  and  disappears.  Before  the  disappear- 
ance of  the  chorda,  the  ossification  of  the  bodies  and  arches  of  the  verte- 
brae begins  at  distinct  points. 

The  ossification  of  the  body  of  a  vertebra  is  first  observed  at  the  point 
where  the  two  primitive  elements  of  the  vertebrae  have  united  inferiorly. 
Those  vertebrae  which  do  not  bear  ribs,  such  as  the  cervical  vertebrae, 
have  generally  an  additional  centre  of  ossification  in  the  transverse  pro- 
cess,  which  is  to  be  regarded  as  an  abortive  rudiment  of  a  rib.  In  the 
foetal  bird,  these  additional  ossified  portions  exist  in  all  the  cervical  ver- 
tebrae, and  gradually  become  so  much  developed  in  the  lower  part  of  the 
cervical  region  as  to  form  the  upper  false  ribs  of  this  class  of  animals. 
The  same  parts  exist  in  mammalia  and  man;  those  of  the  last  cervical 
vertebrae  are  the  most  developed,  and  in  children  may,  for  a  considerable 
period,  be  distinguished  as  a  separate  part  on  each  side,  like  the  root  or 
head  of  a  rib. 

The  true  cranium  is  a  prolongation  of  the  vertebral  column,  and  is 
developed  at  a  much  earlier  period  than  the  facial  bones.  Originally,  it 
is  formed  of  but  one  mass,  a  cerebral  capsule,  the  chorda  dorsalis  being 
continued  into  its  base,  and  ending  there  with  a  tapering  point.  At  an 
early  period  the  head  is  bent  downward  and  forward  round  the  end  of 
the  chorda  dorsalis  in  such  a  Avay  that  the  middle  cerebral  vesicle,  and 
not  the  anterior,  comes  to  occupy  the  highest  position  in  the  head. 

Pituitary  Body. — In  connection  with  this  must  be  mentioned  the 
development  of  the  pituitary  body.  It  is  formed  by  the  meeting  of  two 
outgrowths,  one  from  the  foetal  brain,  which  grows  downward,  and  the 
other  from  the  epiblast  of  the  buccal  cavity,  which  grows  up  toward  it. 
The  surrounding  mesoblast  also  takes  part  in  its  formation.  The  con- 
nection of  the  first  process  with  the  brain  becomes  narrowed,  and  persists 
us  the  infuiidibulum,  while  that  of  the  other  process  witli  the  buccal 


GENERATION  AND  DEVELOPMENT.  273 

cavity  disappears  completely  at  a  spot  corresponding  with  the  future  posi- 
tion of  the  body  of  the  sphenoid. 

The  first  appearance  of  a  solid  support  at  the  base  of  the  cranium  ob- 
served by  Miiller  in  fish,  consists  of  two  elongated  bands  of  cartilage 
(trabeculae  cranii),  one  on  the  right  and  the  other  on  the  left  side,  which 
are  connected  with  the  cartilaginous  capsule  of  the  auditory  apparatus, 
and  which  diverge  to  enclose  the  pituitary  body,  uniting  in  front  to  form 
the  septum  nasi  beneath  the  anterior  end  of  the  cerebral  capsule.  Hence, 
in  the  cranium,  as  in  the  spinal  column,  there  are  at  first  developed  at 
the  sides  of  the  chorda  dorsalis  two  symmetrical  elements,  which  subse- 
quently coalesce,  and  may  wholly  enclose  the  chorda. 

The  brain-case  consists  of  three  segments:  occipital,  parietal,  and 
frontal,  corresponding  in  their  relative  position  to  the  three  primitive  cer- 
ebral vesicles;  it  may  also  be  noted  that  in  front  of  each  segment  is  devel- 
oped a  sense-organ  (auditory,  ocular,  and  olfactory,  from  behind  forward). 
The  basis  cranii  consists  at  an  early  period  of  an  unsegmented  cartilagi- 
nous rod,  developed  round  the  notochord,  and  continued  forward  beyond 
its  termination  into  the  traieculce  cranii,  which  bound  the  pituitary  fossa 
on  either  side. 

In  this  cartilaginous  rod  three  centres  of  ossification  appear:  basi- 
occipital,  basi-sphenoid,  and  pre-sphenoid,  one  corresponding  to  each 
segment. 

The  bones  forming  the  vault  of  the  skull  (frontal,  parietal,  squamous 
portion  of  temporal),  with  the  exception  of  the  squamo-occipital,  which 
is  pre-formed  in  cartilage,  are  ossified  in  membrane. 

Development  of  the  Face  and  Visceral  Arches. 

It  has  been  said  before  that  at  an  early  period  of  development  of  the 
embryo,  there  grow  up  on  the  sides  of  the  primitive  groove  the  so-called 
dorsal  lamincB,  which  at  length  coalesce,  and  complete  by  their  union  the 
spinal  canal.  The  same  process  essentially  takes  place  in  the  head,  so 
as  to  enclose  the  cranial  cavity. 

Visceral  Laminae. — The  so-called  visceral  lamince  have  been  alsa 
described  as  passing  forward,  and  gradually  coalescing  in  front,  as  the 
dorsal  laminae  do  behind,  and  thus  enclosing  the  thoracic  and  abdominal 
cavity.  An  analogous  process  occurs  in  the  facial  and  cervical  regions,  ^ 
but  the  enclosing  laminae,  instead  of  being  simple,  as  in  the  former 
instances,  are  cleft. 

In  this  way  the  so-called  visceral  arches  and  clefts  are  formed,  four  on 
each  side  (Fig.  430,  a). 

From  or  in  connection  with  these  arches  the  following  parts  are  de- 
veloped:— 

Vol.  II.— 18. 


274 


HAKD-BOOK  OF  PHYSIOLOGY. 


The  first  arch  (mandibular)  contains  a  cartilaginous  rod  (Meckel's 
cartilage),  around  the  distal  end  of  which  the  lower  jaw  is  develo23ed, 
while  the  malleus  is  ossified  from  the  proximal  end. 

From  near  the  root  of  this  arch  the  maxillary  process  grows  forward 
and  inward  toward  the  middle  line;  from  it  are  formed  the  superior  max- 
illary and  malar  bones.  A  pair  of  cartilaginous  rods  (pterygo-palatine), 
parallel  to  the  trabeculse  cranii,  give  origin  to  the  external  pterygoid  plate 
of  the  sphenoid  and  the  palate  bones. 

The  cleft  between  the  maxillary  process  and  the  mandibular  (or  first 
visceral  arch)  forms  the  mouth. 

When  the  maxillary  processes  on  the  two  sides  fail  partially  or  com- 
pletely to  unite  in  the  middle  line,  the  well-known  condition  termed  cleft 
palate  results.    When  the  integument  of  the  face  presents  a  similar  defi- 


B 


430.— A.  Magnified  view  from  before  of  the  liead  and  neck  of  a  human  embryo  of  about  three 
weeks  (from  Ecker).  1,  anterior  cerebral  vesicle  or  cerebrum;  2,  middle  ditto;  3,  middle  or  fronto- 
nasal process;  4,  superior  maxillary  process;  5,  eye;  6,  inferior  maxillary  process,  or  fu'st  visceral 
arch,  and  below  it  the  first  cleft;  7, 8, 9,  second,  third,  and  fourth  arches  and  clefts,  b.  Anterior  view 
of  the  head  of  a  hmnan  foetus  of  about  the  fifth  week  (from  Ecker,  as  before.  Fig.  IV.).  1, 2,  3,  5,  the 
same  parts  as  in  a;  4,  the  external  nasal  or  lateral  frontal  process;  6,  the  superior  maxillary  pro- 
cess; 7,  the  lower  jaw;  X,the  tongue;  8,  first  branchial  cleft  becoming  the  meatus  auditorius  ex- 
ternus. 

ciency,  we  have  the  deformity  known  as  liare-lip.  Though  these  two 
deformities  frequently  co-exist,  they  are  by  no  means  always  necessarily 
associated. 

The  upper  part  of  the  face  in  the  middle  line  is  developed  from  the 
so-called  frontal-nasal  process  (a,  3,  Fig.  430).  From  the  second  arch 
are  developed  the  incus,  stapes,  and  stapedius  muscle,  the  st^doid  process 
of  the  temporal  bone,  the  stylo-hyoid  ligament,  and  the  smaller  cornu  of 
the  liyoid  bone.  From  the  tliird  visceral  arch,  the  greater  cornu  and 
lody  of  the  hyoid  bone.  In  man  and  other  mammalia  fourth  visceral 
arcii  is  indistinct.  It  occupies  the  position  where  the  neck  is  afterward 
developed. 

A  distinct  connection  is  traceable  between  these  visceral  arches  and 
certain  cranial  nerves:  the  trigeminal,  the  facial,  the  glosso -pharyngeal, 
and  the  pneumogastric.  The  ophthalmic  division  of  the  trigeminal  sup- 
plies the  trabecular  arch;  the  superior  and  inferior  maxillary  divisions 
supply  the  maxillary  and  mandibular  arches  respectively. 

The  facial  nerve  distributes  one  branch  (chorda  tympani)  to  the  first 
visceral  arch,  and  others  to  the  second  visceral  arch.  Thus  it  divides, 
euclosiiig  the  first  visceral  cleft. 


GENERATION  AND  DEVELOPMENT. 


275 


Similarly,  the  glosso-pliaryngeal  divides  to  enclose  the  second  visceral 
cleft,  its  lingual  branch  being  distributed  to  the  second,  and  its  pharyn- 
geal branch  to  the  third  arch. 


Fig.  431.— For  description  see  Fig.  429. 

The  vagus,  too,  sends  a  branch  (pharyngeal)  along  the  third  arch,  and 
in  fishes  it  gives  off  paired  branches,  which  divide  to  enclose  several  suc- 
cessive branchial  clefts. 

Development  of  the  Exteemities. 

The  extremities  are  developed  in  a  uniform  manner  in  all  vertebrate 
animals.    They  appear  in  the  form  of  leaf -like  elevations  from  the  pari- 


FiG.  432.— A  human  embryo  of  the  fourth  week;  SJ^  lines  in  length.  1,  the  chorion;  3,  part  of  the 
amnion;  4,  umbilical  vesicle  with  its  long  pedicle  passing  into  the  abdomen;  7,  the  heart;  8,  thehver; 
9,  the  visceral  arch  destined  to  form  the  lower  jaw,  beneath  which  are  two  other  visceral  arches 
separated  by  the  branchial  clefts;  10,  rudiment  of  the  upper  extremity;  11,  that  of  the  lower  extremi- 
ty; 12,  the  umbilical  cord;  15,  the  eye;  16,  the  ear;  17,  cerebral  hemispheres;  18,  optic  lobes,  corpora 
quadrigemina.  (Miiller.) 

etes  of  the  trunk  (see  Fig.  432'),  at  points  where  more  or  less  of  an  a^rch 
will  be  produced  for  them  within.    The  primitive  form  of  the  extremity 


276 


HAND-BOOK  OF  PHYSIOLOGY. 


is  nearly  the  same  in  all  Vertebrata,  whether  it  be  destined  for  swim- 
ming, crawling,  walking,  or  flying.  In  the  human  foetus  the  fingers  are 
at  first  united,  as  if  webbed  for  swimming;  but  this  is  to  be  regarded  not 
so  much  as  an  approximation  to  the  form  of  aquatic  animals,  as  the  prim- 
itive form  of  the  hand,  the  individual  parts  of  which  subsequently  become 
more  completely  isolated. 

The  fore-limb  always  appears  before  the  hind-limb  and  for  some  time 
continues  in  a  more  advanced  state  of  development.  In  both  limbs  alike, 
the  distal  segment  (hand  or  foot)  is  separated  by  a  slight  notch  from  the 
proximal  part  of  the  limb,  and  this  part  is  subsequently  divided  again  by 
a  second  notch  (knee  or  elbow-joint). 

Development  of  the  Vascular  System. 

At  an  early  stage  in  the  development  of  the  embryo-chick,  the  so- 
called  ''area  vasculosa"  begins  to  make  its  appearance.  A  number  of 
branched  cells  in  the  mesoblast  send  out  processes  which  unite  so  as  to 
form  a  network  of  protoplasm  with  nuclei  at  the  nodal  points.  A  large 
number  of  the  nuclei  acquire  a  red  color;  these  form  the  red  blood-cells. 
The  protoplasmic  processes  become  hollowed  out  in  the  centre  so  as  to 
form  a  closed  system  of  branching  canals,  in  the  walls  of  which  the  rest 
of  the  nuclei  remain  imbedded.  In  the  blood-vessels  thus  formed,  the 
circulation  of  the  embryonic  blood  commences. 

According  to  Klein's  researches,  the  first  blood-vessels  in  the  chick 
are  developed  from  embryonic  cells  of  the  mesoblast,  which  swell  up  and 
become  vacuolated,  Avhile  their  nuclei  undergo  segmentation.  These 
cells  send  out  protoplasmic  processes,  which  unite  with  corresponding 
ones  from  other  cells,  and  become  hollowed,  give  rise  to  the  capillary  wall 
composed  of  endothelial  cells;  the  blood-corpuscles  being  budded  off  from 
the  endothelial  wall  by  a  process  of  gemmation. 

Heart. — About  the  same  time  the  heart  makes  its  appearance  as  a 
solid  mass  of  cells  of  the  splanchnopleure. 

At  this  period  the  anterior  part  of  the  alimentary  tube  ends  blindly 
beneath  the  notochord.  It  is  beneath  the  posterior  end  of  this  "fore-out'* 
(as  it  may  be  termed)  that  the  heart  begins  to  be  developed.  A  cavity  is 
hollowed  out  longitudinally  in  the  mass  of  cells;  the  central  cells  float 
freely  in  the  fluid,  which  soon  begins  to  circulate  by  means  of  the  rhyth- 
mic pulsations  of  the  embryonic  heart. 

These  pulsations  take  place  even  before  the  appearance  of  a  cavity, 
and  immediately  after  the  first  "laying  down"  of  the  cells  from  which  the 
heart  is  formed,  and  long  before  muscular  fibres  or  ganglia  liave  been 
formed  in  the  cardiac  walls.  At  first  they  seldom  exceed  from  fifteen  to 
eighteen  in  tlie  minute.  The  fluid  witliin  the  cavity  of  the  heart  shortly 
assumes  tlie  characters  of  blood.    At  the  same  time  the  cavity  itself 


GENERATION  AND  DEVELOPMENT. 


277 


forms  a  communication  with  the  great  vessels  in  contact  with  it,  and  the 
cells  of  which  its  walls  are  composed  are  transformed  into  fibrous  and 
muscular  tissues,  and  into  epithelium.  In  the  developing  chick  it  can  be 
observed  with  the  naked  eye  as  a  minute  red  pulsating  point  before  the 
end  of  the  second  day  of  incubation. 

Blood-vessels. — Blood-vessels  appear  to  be  developed  in  two  ways, 
according  to  the  size  of  the  vessels.  In  the  formation  of  large  blood- 
vessels, masses  of  embryonic  cells  similar  to  those  from  which  the  heart 


still  containing  granules  of  fat.    x  350  times.  (Kolliker.) 

and  other  structures  of  the  embryo  are  developed,  arrange  themselves  in 
the  position,  form,  and  thickness  of  the  developing  vessel.  Shortly  after- 
ward the  cells  in  the  interior  of  a  column  of  this  kind  seem  to  be  devel- 
oped into  blood-corpuscles,  while  the  external  layer  of  cells  is  converted 
into  the  walls  of  the  vessel. 

Capillaries. — In  the  development  of  capillaries  another  plan  is  pur- 
sued. This  has  been  well  illustrated  by  Kolliker,  as  observed  in  the  tails 
of  tadpoles.    The  first  lateral  vessels  of  the  tail  have  the  form  of  simple 


278 


HAND-BOOK  OF  PHYSIOLOGY. 


arches,  passing  between  the  main  artery  and  vein,  and  are  produced  by 
the  junction  of  prolongations,  sent  from  both  the  artery  and  vein,  with 
certain  elongated  or  star-shaped  cells,  in  the  substance  of  the  tail.  When 
these  arches  are  formed  and  are  permeable  to  blood,  new  prolongations 
pass  from  them,  join  other  radiated  cells,  and  thus  form  secondary  arches 


Fig.  434.  Fig.  435. 

Fig.  434.— Development  of  capillaries  in  the  regenerating  tail  of  a  tadpole,  a,  6,  c,  d,  sprouts  and 
cords  of  protoplasm.  (Arnold.) 

Fig.  435. — The  same  region  after  the  lapse  of  24  hours.  The  "sprouts  and  cords  of  protoplasm"" 
have  become  channeled  out  into  capillaries.  (Arnold.) 


(Fig.  434).  In  this  manner,  the  capillary  network  extends  in  proportion 
as  the  tail  increases  in  length  and  breadth,  and  it,  at  the  same  time,  be- 
comes more  dense  by  the  formation,  according  to  the  same  plan,  of  fresh 
vessels  within  its  meshes.  The  prolongations  by  which  the  vessels  com- 
municate with  the  star-shaped  cells,  consist  at  first  of  narrow  pointed 


projections  from  the  side  of  the  vessels,  which  gradually  elongate  until 
they  come  in  contact  with  the  radiated  processes  of  the  cells.  The  thick- 
ness of  such  a  prolongation  often  does  not  exceed  that  of  a  fibril  of  fibrous 


GENERATION  AND  DEVELOPMENT. 


279 


tissue,  and  at  first  it  is  perfectly  solid;  but,  by  degrees,  especially  after 
its  junction  with  a  cell,  or  with  another  prolongation,  or  with  a  vessel 
already  permeable  to  blood,  it  enlarges,  and  a  cavity  then  forms  in  its 
interior  (see  Figs.  434,  435).  This  tissue  is  well  calculated  to  illustrate 
the  various  steps  in  the  development  of  blood-vessels  from  elongating  and 
branching  cells. 

In  many  cases  a  whole  network  of  capillaries  is  developed  from  a  net- 
work of  branched,  embryonic  connective-tissue  corpuscles  bv  the  joining 
of  their  processes,  the  multiplication  of  their  nuclei,  and  the  vacuolation 


Fig.  437. — FcBtal  heart  in  successive  stages  of  development.  1,  venous  extremity;  3,  arterial  ex- 
tremity; 3,  3,  pulmonary  branches;  4,  ductus  arteriosus.  (Dalton.) 

of  the  cell-substance.  The  vacuoles  gradually  coalesce  till  all  the  parti- 
tions are  broken  down  and  the  originally  solid  protoplasmic  cell-substance 
is,  so  to  speak,  tunneled  out  into  a  number  of  tubes. 

Capillaries  may  also  be  developed  from  cells  which  are  originally 
spheroidal,  vacuoles  form  in  the  interior  of  the  cells,  gradually  becoming 
united  by  fine  protoplasmic  processes:  by  the  extension  of  the  vacuoles 
into  them,  capillary  tubes  are  gradually  formed. 

Morphology.  Heart. — When  it  first  appears,  the  heart  is  approximate- 
ly tubular  in  form.  It  receives  at  its  two  posterior  angles  the  two  omphalo- 
mesenteric veins,  and  gives  off  anteriorly  the  primitive  aorta  (Fig.  437). 

It  soon,  however,  becomes  curved  somewhat  in  the  shape  of  a  horse- 
shoe, with  the  convexity  toward  the  right,  the  venous  end  being  at  the 
same  time  drawn  up  toward  the  head,  so  that  it  finally  lies  behind  and 
somewhat  to  the  right  of  the  arterial.  It  also  becomes  partly  divided  by 
constrictions  into  three  cavities. 

Of  these 'three  cavities  which  are  developed  in  all  Vertebrata,  that  at 
the  venous  end  is  the  simple  auricle,  that  at  the  arterial  end  the  bulbus 
arteriosus,  and  the  middle  one  is  the  simple  ventricle. 

These  three  parts  of  the  heart  contract  in  succession.  The  auricle  and 
the  bulbus  arteriosus  at  this  period  lie  at  the  extremities  of  the  horseshoe. 


280 


HAND-BOOK  OF  PHYSIOLOGY. 


Tlie  bulging  out  of  the  middle  portion  inferiorly  gives  the  first  indication 
of  the  future  form  of  the  ventricle  (Fig.  438).  The  great  curvature  of 
the  horseshoe  by  the  same  means  becomes  much  more  developed  than  the 
smaller  curvature  between  the  auricle  and  bulbus;  and  the  two  extremi- 
ties, the  auricle  and  bulb,  approach  each  other  superiorly,  so  as  to  produce 
a  greater  resemblance  to  the  later  form  of  the  heart,  whilst  the  ventricle 
becomes  more  and  more  developed  inferiorly.  The  heart  of  Fishes  retains 
these  three  cavities,  no  further  division  by  internal  septa  into  right  and 
left  chambers  taking  place.  In  Amphibia,  also,  the  heart  throughout  life 
consists  of  the  three  muscular  divisions  which  are  so  early  formed  in  the 
embryo;  but  the  auricle  is  divided  internally  by  a  septum  into  a  pulmo- 
nary and  systemic  auricle.  In  Eeptiles,  not  merely  the  auricle  is  thus 
divided  into  two  cavities,  but  a  similar  septum  is  more  or  less  developed 


Fig.  438.— Heart  of  the  chick  at  the  45th,  65th,  and  85th  hours  of  incubation.  1,  the  venous  trunks; 
2,  the  auricle;  3,  the  ventricle;  4,  the  bulbus  arteriosus.   (Allen  Thomson.) 

in  the  ventricle.  In  Birds  and  Mammals,  both  auricle  and  ventricle 
undergo  complete  division  by  septa;  whilst  in  these  animals  as  well  as  in 
reptiles,  the  bulbus  aortse  is  not  permanent,  but  becomes  lost  in  the  ven- 
tricles. The  septum  dividing  the  ventricle  commences  at  the  apex  and 
extends  upward.  The  subdivision  of  the  auricles  is  very  early  fore- 
shadowed by  the  outgrowth  of  the  two  auricular  appendages,  which  occurs 
before  any  septum  is  formed  externally.  The  septum  of  the  auricles  is 
developed  from  a  semilunar  fold,  which  extends  from  above  downward. 
In  man,  the  septum  between  the  ventricles,  according  to  Meckel,  begins 
to  be  formed  about  the  fourth  week,  and  at  the  end  of  eight  weeks  is 
complete.  The  septum  of  the  auricles,  in  man  and  all  animals  which 
possess  it,  remains  imperfect  throughout  foetal  life.  When  the  partition 
of  the  auricles  is  first  commencing,  the  two  venae  cav«  have  different 
relations  to  the  two  cavities.  The  superior  cava  enters,  as  in  the  adult, 
into  the  right  auricle;  but  the  inferior  cava  is  so  placed  that  it  appears 
to  enter  the  left  auricle,  and  the  posterior  part  of  the  septum  of  the  auri- 
cles is  formed  by  the  Eustachian  valve,  which  extends  from  the  point  of 
entrance  of  the  inferior  cava.  Subsequently,  however,  the  septum,  grow- 
ing from  the  anterior  wall  close  to  the  upper  end  of  the  ventricular  sep- 
tum, becomes  directed  more  and  more  to  the  left  of  the  vena  cava  inferior. 
During  the  entire  period  of  footal  life,  there  remains  an  opening  in  the 
sei)tum,  which  the  valve  of  the  foramen  ovale,  developed  in  the  third 
moiitli,  imperfectly  closes. 


GENERATION  AND  DEVELOPMENT. 


281 


Bulbus  Arteriosus. — The  luTbus  arteriosus  which  is  originally  a 
single  tube,  becomes  gradually  divided  into  two  by  the  growth  of  an  in- 
ternal septum,  which  springs  from  the  posterior  wall,  and  extends  forward 
toward  the  front  wall  and  downward  toward  the  ventricles.  This  parti- 
tion takes  a  somewhat'  spiral  direction,  so  that  the  two  tubes  (aorta  and 
pulmonary  artery)  which  result  from  its  completion,  do  not  run  side  by 
side,  but  are  twisted  round  each  other. 

As  the  septum  grows  down  toward  the  ventricles,  it  meets  and  coalesces 
with  the  upwardly  growing  ventricular  septum,  and  thus  from  the  right 
and  left  ventricles,  which  are  now  completely  separate,  arise  respectively 
the  pulmonary  artery  and  aorta,  which  are  also  quite  distinct.  The  au- 
riculo-ventricular  and  semilunar  valves  are  formed  by  the  growth  of  folds 
of  the  endocardium. 

At  its  first  appearance  the  heart  is  placed  just  beneath  the  head  of 
the  foetus,  and  is  very  large  relatively  to  the  whole  body:  but  with  the 
growth  of  the  neck  it  becomes  further  and  further  removed  from  the  head, 
and  lodged  in  the  cavity  of  the  thorax. 

Up  to  a  certain  period  the  auricular  is  larger  than  the  ventricular 
division  of  the  heart;  but  this  relation  is  gradually  reversed  as  develop- 
ment proceeds.  Moreover,  all  through  foetal  life,  the  walls  of  the  right 
ventricle  are  of  very  much  the  same  thickness  as  those  of  the  left,  which 
may  probably  be  explained  by  the  fact  that  in  the  foetus  the  right  ventri- 
cle has  to  propel  the  blood  from  the  pulmonary  artery  into  the  aorta,  and 
thence  into  the  placenta,  while  in  the  adult  it  only  drives  the  blood 
through  the  lungs. 

Arteries. — The  primitive  aorta  arises  from  the  bulbus  arteriosus 
and  divides  into  two  branches  which  arch  backward,  one  on  each  side  of 
the  foregut,  and  unite  again  behind  it,  and  in  front  of  the  notochord,  into 
a  single  vessel. 

This  gives  off  the  two  omphalo-mesenteric  arteries,  which  distribute 
branches  all  over  the  yolk-sac;  this  area  vasculosa  in  the  chick  attaining 
a  large  development,  and  being  limited  all  round  by  a  vessel  known  as 
the  sinus  terminalis. 

The  blood  is  collected  by  the  venous  channels,  and  returned  through 
the  omphalo-mesenteric  veins  to  the  heart. 

Behind  this  pair  of  primitive  aortic  arches,  four  more  pairs  make  their 
appearance  successively,  so  that  there  are  five  pairs  in  all,  each  one  run- 
ning along  one  of  the  visceral  arches. 

These  five  are  never  all  to  be  seen  at  once  in  the  embryo  of  higher 
animals,  for  the  two  anterior  pairs  gradually  disappear,  while  the  pos- 
terior ones  are  making  their  appearance,  so  that  at  length  only  three 
remain. 

In  Fishes,  however,  they  all  persist  throughout  life  as  the  branchial 


282 


HAND-BOOK  OF  PHYSIOLOaY. 


arteries  supplying  the  gills,  while  in  Amphibia  three  pairs  persist  through- 


In  Keptiles,  Birds,  and  Mammals,  further  transformations  occur. 

In  Reptiles  the  fourth  pair  remains  throughout  life  as  the  permanent 
right  and  left  aorta;  in  Birds  the  right  one  remains  as  the  permanent 
aorta,  curving  over  the  ri^ht  bronchus  instead  of  the  left  as  in  Mammals. 

In  Mammals  the  left  fourth  aortic  arch  develops  into  the  perma- 
nent aorta,  the  right  one  remaining  as  the  subclavian  artery  of  that  side. 
Thus  the  subclavian  artery  on  the  right  side  corresponds  to  the  aortic  arch 


Fig.  439.— Diagram  of  the  aortic  arches  in  a  mammal,  showing  transformations  which  give  rise 
to  the  permanent  arterial  vessels.  A,  primitive  arterial  stem  or  aortic  bulb,  now  divided  into  A,  the 
ascending  part  of  the  aortic  arch,  and  p,  the  pulmonary;  a  a',  right  and  left  aortic  roots:  A\  de- 
scending aorta;  1,  2,  3,  4,  5,  the  five  primitive  aortic  or  branchial  arches;  /.  77,  777,  IV,  the  four 
branchial  clefts  which,  for  the  sake  of  clearness,  have  been  omitted  on  the  right  side.  The  perma- 
nent systemic  vessels  are  deeply,  the  pulmonary  arteries,  Ughtly  shaded;  the  parts  of  the  primitive 
arches  which  are  transitory  are  simply  outlined;  c,  placed  between  the  permanent  common  carotid 
arteries;  c  e,  external  carotid  arteries;  c  t,  internal  carotid  arteries;  s,  right  subclavian,  rising  from 
the  right  aortic  root  beyond  the  fifth  arch;  f,  right  vertebral  from  the  same,  opposite  the  fourth 
arch;  v'  s\  left  vertebral  and  subclavian  arteries  rising  together  from  the  left,  or  permanent  aortic 
root,  opposite  the  fourth  arch;  p,  pulmonary  arteries  rising  together  from  the  left  fifth  arch ;  d, 
outer  or  back  part  of  left  fifth  arch,  forming  ductus  arteriosus;  j>  n,  p  u,  right  and  left  pneumogas- 
tric  nerves,  descending  in  front  of  aortic  arches,  with  their  recurrent  brancnes  represented  diagram- 
matically  as  passing  .behind,  to  illustrate  the  relations  of  these  nerves  respectively  to  the  right  sub- 
clavian artery  (4),  and  the  arch  of  the  aorta  and  ductus  arteriosus  (d).  (Allen  Thomson,  after 
Rathke.) 


on  the  left,  and  this  homology  is  further  confirmed  by  the  fact  that  the 
recurrent  laryngeal  nerve  hooks  under  the  subclavian  on  the  right  side, 
and  the  aortic  arch  on  the  left. 

The  third  aortic  arch  remains  as  the  external  carotid  artery,  while  the 
fifth  disappears  on  the  riglit  side,  but  on  the  loft  forms  the  pulmonary  ar- 
tery. The  distal  end  of  this  arch  originally  o})ens  into  the  descending  aorta, 
and  this  communication  (which  is  permanent  tliroughout  life  in  many  rep- 
tiles on  both  sides  of  the  body)  remains  throughout  fcrtal  life  under  tlie 
name  of  ductus  arterio.sm:  the  branches  of  the  pulmonary  artery  to  tlie 


out  life. 


GENERATION  AND  DEVELOPMENT. 


283 


right  and  left  lung  are  very  small,  and  most  of  the  blood  which  is  forced 
into  the  pulmonary  artery  passes  through  the  wide  ductus  arteriosus  into 
the  descending  aorta.  All  these  points  will  become  clear  on  reference  to 
the  preceding  diagram  (Fig.  439). 

As  the  umbilical  vesicle  dwindles  in  size,  the  portion  of  the  omphalo- 
mesenteric arteries  outside  the  body  gradually  disappears,  the  part  inside 
the  body  remaining  as  the  mesenteric  arteries  (Figs.  440,  441). 

Meanwhile  with  the  growth  of  the  allantois  two  new  arteries  (umbilical) 
appear,  and  rapidly  increase  in  size  till  they  are  the  largest  branches  of 


Fig.  440. — Diagram  of  young  embryo  and  its  vessels,  showing  course  of  circulation  in  the  umbili- 
cal vesicle;  and  also  that  of  the  allantois  (near  the  caudal  extremity),  which  is  just  commencing. 
(Dalton.) 

Fia.  441. — Diagram  of  embryo  and  its  vessels  at  a  later  stage,  showing  the  second  circulation. 
The  pharynx,  oesophagus,  and  intestinal  canal  have  become  further  developed,  and  the  mesenteric 
arteries  have  enlarged,  while  the  umbilical  vesicle  and  its  vascular  branches  are  very  much  reduced 
in  size.   The  large  umbilical  arteries  are  seen  passing  out  in  the  placenta.  (Dalton.) 


the  aorta:  they  are  given  off  from  the  internal  iliac  arteries,  and  for  a  long 
time  are  considerably  larger  than  the  external  iliacs  which  supply  the  com- 
paratively small  hind-limbs. 

Veins. — The  chief  veins  in  the  early  embryo  may  be  divided  into  two 
groups,  visceral  and  parietal:  the  former  includes  the  omphalo-mesenteric 
and  umbilical,  the  latter  the  jugular  and  cardinal  veins.  The  former  may 
be  first  considered. 

The  earliest  veins  to  appear  in  the  foetus  are  the  omphalo-mesenteric, 
which  return  the  blood  from  the  yolk-sac  to  the  developing  auricle.  As 
soon  as  the  placenta  with  its  umbilical  veins  is  developed,  these  unite  with 
the  omphalo-mesenteric,  and  thus  the  blood  which  reaches  the  auricle 
comes  partly  from  the  yolk-sac  and  partly  from  the  placenta.  The  right 
omphalo-mesenteric  and  the  right  umbilical  vein  soon  disappear,  and  the 
united  left  omphalo-mesenteric  and  umbilical  veins  pass  through  the 
developing  liver  on  the  way  to  the  auricle.  Two  sets  of  vessels  make 
their  appearance  in  connection  with  the  liver  (venas  hepatic^e  advehentes. 


284 


HAND-BOOK  OF  PHYSIOLOGY. 


and  revehentes),  both  opening  into  the  united  omphalo-mesenteric  and 
umbilical  veins,  in  such  a  way  that  a  portion  of  the  venous  blood  travers- 
ing the  latter  is  diverted  into  the  developing  liver,  and,  having  passed 
through  its  capillaries,  returns  to  the  umbilical  vein  through  the  venae 
hepaticae  revehentes  at  a  point  nearer  the  heart  (see  Fig.  442).  The  por- 
tion of  vein  between  the  afferent  and  efferent  veins  of  the  liver  becomes 
the  ductus  venosus.  The  venae  hepaticae  advehentes  become  the  right  and 
left  branches  of  the  portal  vein,  the  venae  hepaticae  revehentes  become 
the  hepatic  veins,  which  open  just  at  the  junction  of  the  ductus  venosus 
with  another  large  vein  (vena  cava  inferior),  which  is  now  being  developed. 
The  mesenteric  portion  of  the  omphalo-mesenteric  vein  returning  blood 
from  the  developing  intestines  remains  as  the  mesenteric  vein,  which,  by 
its  union  with  the  splenic  vein,  forms  the  portal. 


Fig.  442.— Diagrams  illustrating  the  development  of  veins  about  the  liver.  B,  d  c,  ducts  \S. 
Cuvier,  right  and  left;  c  a,  right  and  left  cardinal  veins;  o,  left  omphalo-mesenteric  vein;  o',  ri^t 
omphalo-mesenteric  vein,  almost  shriveled  up  ;  ^^,  u\  umbilical  veins,  of  which  u',  the  right  one,  has 
almost  disappeared.  Between  the  venae  cardinales  is  seen  the  outline  of  the  rudimentary  hver,  with 
its  venae  hepaticae  advehentes,  and  revehentes;  Z),  ductus  venosus;  Z',  hepatic  veins;  c  vena  cava 
inferior;  P,  portal  vein;  P'  P',  venae  advehentes;      mesenteric  veins.  (Kolliker.) 


Thus  the  foetal  liver  is  supplied  with  venous  blood  from  two  sources, 
through  the  umbilical  and  portal  vein  respectively.  At  birth  the  cir- 
culation through  the  umbilical  vein  of  course  completely  ceases  and  the 
vessel  begins  at  once  to  dwindle,  so  that  now  the  only  venous  supply  of 
the  liver  is  through  the  portal  vein.  The  earliest  appearance  of  the 
parietal  system  of  veins  is  the  formation  of  two  short  transverse  veins 
(ducts  of  Cuvier)  opening  into  the  auricle  on  either  side,  which  result 
from  the  union  of  a  jugular  vein,  collecting  blood  from  the  head  and 
neck,  and  a  cardinal  vein  which  returns  the  blood  from  the  AVolffian 
bodies,  the  vertebral  column,  and  the  parietes  of  the  trunk.  This 
arrangement  persists  throughout  life  in  Fishes,  but  in  ]\Iammals  the  fol- 
lowing transformations  occur. 

As  the  kidneys  are  devolo])ing  a  new  vein  appears  (vena  cava  inferior), 
formed  by  the  junction  of  their  efferent  veins.  It  receives  branches  from 
the  legs  (iliac)  and  increases  rapidly  in  size  as  they  grow:  further  up  it 
receives  the  hepatic  veins.    Tlie  heart  gradually  descends  into  tlie  thorax. 


GENERATION  AND  DEVELOPMENT. 


285 


causing  the  ducts  of  Cuvier  to  become  oblique  instead  of  transverse.  As 
the  fore-limbs  develop,  the  subclavian  veins  are  formed. 

A  transverse  communicating  trunk  now  unites  the  two  ducts  of  Cuvier, 
and  gradually  increases,  while  the  left  duct  of  Cuvier  becomes  almost 
entirely  obliterated  (all  its  blood  passing  by  the  communicating  trunk  to 
the  right  side)  (Fig.  443,  c,  d).  The  right  duct  of  Cuvier  remains  as 
the  right  innominate  vein,  while  the  communicating  branch  forms  the 
left  innominate.    The  remnant  of  the  left  duct  of  Cuvier  generally  re- 


A  B  C  D 


Fig.  443.— Diagrams  illustrating  the  development  of  the  great  veins,  d  c,  ducts  of  Cuvier;  j\ 
jugular  veins;  h,  hepatic  veins;  c,  cardinal  veins;  s,  subclavian  vein;  j  i,  internal  jugular  vein;  J  e, 
external  jugtilar  vein;  a  z,  azygos  vein;  ci,  inferior  vena  cava;  r,  renal  veins;  *  I,  niac  veins;  h  ij, 
hypogastric  veins.  (Gegenbaur.) 

mains  as  a  fibrous  band,  running  obliquely  down  to  the  coronary  vein, 
which  is  really  the  proximal  part  of  the  left  duct  of  Cuvier.  In  front  of 
the  root  of  the  left  lung,  another  relic  may  be  found  in  the  form  of  the 
so-called  vestigial  fold  of  Marshall,  which  is  a  fold  of  pericardium  running 
in  the  same  direction. 

In  many  of  the  lower  mammals,  such  as  the  rat,  the  left  ductus 
Cuvieri  remains  as  a  left  superior  cava. 

Meanwhile,  a  transverse  branch  carries  across  most  of  the  blood  of  the 
left  cardinal  vein  into  the  right;  and  by  this  union  the  great  azygos  vein 
is  formed. 

The  upper  portions  of  the  left  cardinal  vein  remain  as  the  left  superior 
intercostal  and  vena  azygos  minor  (Fig.  443,  d). 


286 


HAND-BOOK  OF  PHYSIOLOGY. 


CiRCULATIOlT  OF  BlOOD  IN"  THE  FcETUS. 

The  circulation  of  blood  in  the  foetus  differs  considerably  from  that 
of  the  adult.  It  will  be  well,  perhaps,  to  begin  its  description  by  tracing 
the  course  of  the  blood,  which,  after  being  carried  out  to  the  placenta  by 
the  two  umbilical  arteries,  has  returned,  cleansed  and  replenished,  to  the 
foetus  by  the  umbilical  vein. 

It  is  at  first  conveyed  to  the  under  surface  of  the  liver,  and  there  the 
stream  is  divided, — a  part  of  the  blood  passing  straight  on  to  the  inferior 
vena  cava,  through  a  venous  canal  called  the  ductus  venosus,  while  the 
remainder  passes  into  the  portal  vein,  and  reaches  the  inferior  vena  cava 
only  after  circulating  through  the  liver.  Whether,  however,  by  the  direct 
route  through  the  ductus  venosus  or  by  the  roundabout  way  through  the 
liver, — all  the  blood  which  is  returned  from  the  placenta  by  the  umbilical 
vein  reaches  the  inferior  vena  cava  at  last,  and  is  carried  by  it  to  the  right 
auricle  of  the  heart,  into  which  cavity  is  also  pouring  the  blood  that  has 
circulated  in  the  head  and  neck  and  arms,  and  has  been  brought  to  the 
auricle  by  the  superior  vena  cava.  It  might  be  naturally  expected  that 
the  two  streams  of  blood  would  be  mingled  in  the  right  auricle,  but  such  is 
not  the  case,  or  only  to  a  slight  extent.  The  blood  from  the  superior 
vena  cava — the  less  pure  fluid  of  the  two — passes  almost  exclusively  into 
the  right  ventricle,  through  the  auriculo-ventricular  opening,  just  as  it 
does  in  the  adult;  while  the  blood  of  the  inferior  vena  cava  is  directed  by 
a  fold  of  the  lining  membrane  of  the  heart,  called  the  Eustachian  valve, 
through  the  foramen  ovale  into  the  left  auricle,  whence  it  passes  into  the 
left  ventricle,  and  out  of  this  into  the  aorta,  and  thence  to  all  the  body. 
The  blood  of  the  superior  vena  cava, .  which,  as  before  said,  passes  into 
the  right  ventricle,  is  sent  out  thence  in  small  amount  through  the  pul- 
monary artery  to  the  lungs,  and  thence  to  the  left  auricle,  as  in  the  adult. 
The  greater  part,  however,  by  far,  does  not  go  to  the  lungs,  but  instead, 
passes  through  a  canal,  the  ductus  arteriosus,  leading  from  the  pulmo- 
nary artery  into  the  aorta  just  below  the  origin  of  the  three  great  vessels 
which  supply  the  upper  parts  of  the  body;  and  there  meeting  that  part 
of  the  blood  of  the  inferior  vena  cava  which  has  not  gone  into  these  large 
vessels,  it  is  distributed  with  it  to  the  trunk  and  lower  parts, — a  portion 
passing  out  by  way  of  the  two  umbilical  arteries  to  the  placenta.  From 
the  placenta  it  is  returned  by  the  umbilical  vein  to  the  under  surface  of 
the  liver,  from  which  the  description  started. 

Changes  after  Birth. — After  birth  the  foramen  ovale  closes,  and  so 
do  the  ductus  arteriosus  and  ductus  venosus,  as  well  as  the  umbilical 
vessels;  so  that  the  two  streams  of  blood  which  arrive  at  the  right 
auricle  by  the  superior  and  inferior  vena  cava  res})ectively,  thenceforth 


GENERATION  AND  DEVELOPMENT. 


287 


mingle  in  tliis  cavity  of  the  heart,  and  passing  into  tlie  right  ventricle, 
go  by  way  of  the  pulmonary  artery  to  the  lungs,  and  through  these,  after 
purification,  to  the  left  auricle  and  ventricle,  to  be  distributed  over  the 
body.    (See  Chapter  on  Circulation.) 


Fig.  444. — Diagram,  of  the  Foetal  Circulation. 


Deyelopmejtt  of  the  Nervous  System. 

Nerves. — All  the  spinal  nerves  are  derived  from  the  mesoblast;  also 
all  the  cranial  nerves,  except  the  optic  and  olfactory,  which  are  out- 
growths of  the  anterior  cerebral  vesicles.  From  the  same  middle  layer  of 
the  embryo  are  also  derived  the  ganglia  connected  with  these  nerves,  and 
the  whole  sympathetic  system  of  nerves  and  ganglia. 

Spinal  Cord. — Both  the  brain  and  spinal  cord  have  a  different  origin 


288 


HAND-BOOK  OF  PHYSIOLOGY. 


from  that  of  the  nerves  which  arise  from  them.  These  nerve-centres  are 
developed  entirely  from  the  epiblast  (possibly,  however,  a  portion  of  the 
spinal  cord  originates  in  the  mesoblast);  while  the  nerves,  as  we  have 
seen,  are  formed  from  mesoblast.  The  spinal  cord  is  developed  out  of 
the  primitive  medullary  tube  which  results  from  the  folding  in  of  the 
dorsal  laminae  (m,  Fig.  411). 

Soon  after  it  has  closed  in,  this  tube  is  found  to  be  somewhat  oval  in 
section,  with  a  central  canal,  which,  in  sections,  presents  the  appearance 
of  an  elongated  slit,  slightly  expanded  at  each  end.  The  two  opposite 
sides  unite  (Fig.  445)  in  the  centre  of  the  slit,  dividing  it  into  an  anterior 
portion  (the  permanent  central  canal  of  the  cord)  and  a  posterior,  which 
makes  its  way  to  the  free  surface,  and  persists  as  the  posterior  fissure  of 
the  cord,  lodging  a  very  fine  process  of  pia  mater. 

At  this  period  the  cord  consists  almost  entirely  of  grey  matter,  but  the 
white  matter,  which  is  derived  probably  from  the  surrounding  mesoblast, 
becomes  deposited  around  it  on  all  sides,  growing  up  especially  on  the 


Fig.  445.— Diagram  of  development  of  spinal  cord;  cc,  central  canal;  a/,  anterior  fissure;  p/,  pos- 
terior fissure;  y,  grey  matter;  w,  white  matter.  For  further  explanation  see  text. 

anterior  surface  of  the  cord  into  the  two  anterior  columns.  These  are 
separated  by  a  fissure  (anterior  fissure  of  cord),  which  of  course  deepens 
as  the  columns  bounding  it  become  more  prominent  (Fig.  445). 

By  the  development  of  various  commissures,  the  cord  is  completed. 

When  it  first  appears,  the  spinal  cord  occupies  the  whole  length  of  the 
medullary  canal,  but  as  development  proceeds,  the  spinal  column  grows 
more  rapidly  than  the  contained  cord,  so  that  the  latter  appears  as  if 
drawn  up  till,  at  birth,  it  is  opposite  the  third  lumbar  vertebra,  and  in 
the  adult  opposite  the  first  lumbar.  In  the  same  way  the  increasing 
obliquity  of  the  spinal  nerves  in  the  neural  canal,  as  we  approach  the 
lumbar  region,  and  the  ^'cauda  equina"  at  the  lower  end  of  the  cord,  are 
accounted  for. 

Brain. — We  have  seen  (p.  257,  Vol.  II.)  that  the  front  portion  of  the 
medullary  canal  is  almost  from  the  first  widened  out  and  divided  into 
three  vesicles.  From  the  anterior  vesicle  (thalamencephalon)  the  two 
primary  optic  vesicles  are  budded  off  laterally:  their  further  history  will 
bo  traced  in  the  next  section.  Somewhat  later,  from  the  same  vesicle 
the  rudiments  of  the  hemisplieres  appear  in  the  form  of  two  outgrowths 
at  a  higher  level,  which  grow  upward  and  backward.  These  form  the 
2)rosencep7ialo?i, 


GENERATION  AND  DEVELOPMENT. 


28^ 


In  the  walls  of  the  posterior  (third)  cerebral  vesicle,  a  thickening 
appears  (rudimentary  cerebellum)  which  becomes  separated  from  the  rest 
of  the  vesicle  by  a  deep  inflection. 

At  this  time  there  are  two  chief  curvatures  of  the  brain  (Fig.  446,  3). 
(1.)  A  sharp  bend  of  the  whole  cerebral  mass  downward  round  the  end 
of  the  notochord,  by  which  the  anterior  vesicle,  which  was  the  highest  of 


Fig.  446,— Early  stages  in  development  of  human  brain  (magnified).  1,  2,  3,  are  from  an  embryo 
about  seven  weeks  old;  4,  about  three  months  old.  m,  middle  cerebral  vesicle  (mesencephalon);  c, 
cerebellum;  mo.  medulla  oblongata;  i,  thalamencephalon;  ^,  hemispheres;  i',  infundibulum.  Fig. 
3  shows  the  several  curves  which  occur  in  the  course  of  development.  Fig.  4  is  a  lateral  view,  show- 
ing the  great  enlargement  of  the  cerebral  hemispheres  which  have  covered  in  the  thalami,  leaving  the 
optic  lobes,  m,  imcovered.  (Kolliker.) 

N.B. — In  Fig.  2  the  line  i  terminates  in  the  right  hemisphere;  it  ought  to  be  continued  into  the 
thalamencephalon. 


the  three,  is  bent  downward,  and  the  middle  one  comes  to  occupy  the 
highest  position.  (2.)  A  sharp  bend,  with  the  convexity  forward,  which 
runs  in  from  behind  beneath  the  rudimentary  cerebellum  separating  it. 
from  the  medulla. 

Thus,  five  fundamental  parts  of  the  foetal  brain  may  be  distinguished, 
which,  together  with  the  parts  developed  from  them  may  be  presented  in. 
the  following  tabular  view. 

Table  of  Parts  Developed  from  Fundamental  Parts  of  Brain, 

'Cerebral   hemispheres,  corpora. 


1.  Anterior  f  ^'  Prosencephalon. 


Primary  ■{ 


striata,  corpus  callosum,  for- 
nix, lateral  ventricles,  olfac- 
tory bulb  (Rhinencephalon). 


[2.  Thalamencephalon 


(Diencephalon. ) 


Vol.  II.— 19. 


290 


HAND-BOOK  OF  PHYSIOLOGY. 


II.  Middle 


Corpora  quadrigemina,  crura 
cerebri,  aqueduct  of  Sylvius, 
optic  nerve  (secondarily). 


Primary 
Vesicle. 


3.  Mesencephalon. 


III.  Posterior 
Primary 
Vesicle. 


4.  Epencephalon. 

5.  Metencephalon. 


Cerebellum,  pons  Varolii,  ante- 
rior part  of  fourth  ventricle. 


Medulla  oblongata,  fourth  ven- 
tricle, auditory  nerve. 


(Quain's  Anatomy.) 


The  cerebral  hemispheres  grow  rapidly  upward  and  backward,  while 
from  their  inferior  surface  the  olfactory  bulbs  are  budded  off,  and  the 
thalamencephalon,  from  which  they  spring,  remains  to  form  the  third  ven- 
tricle and  optic  thalami.  The  middle  cerebral  vesicle  (mesencephalon) 
for  some  time  is  the  most  prominent  part  of  the  foetal  brain,  and  in 


Fig.  447.— Side  view  of  foetal  brain  at  six  montlis,  showing  commencement  of  formation  of  the 
principal  fissures  and  convolutions.  F,  frontal  lobe;  P,  parietal;  O,  occipital;  T,  temporal;  a  a  a,  com- 
mencing frontal  convolutions;  s,  Sylvian  fissure;  s\  its  anterior  division;  c,  within  it  the  central  lobe 
or  island  of  Reil;    fissure  of  Rolando;  p,  perpendicular  fissure.   (R.  Wagner.) 


Fishes,  Amphibia,  and  Eeptiles,  it  remains  uncovered  through  life  as  the 
optic  lobes.  But  in  Birds  the  growth  of  the  cerebral  hemispheres  thrusts 
the  optic  lobes  down  laterally,  and  in  Mammalia  completely  overlaps 
them. 

In  the  lower  Mammalia  the  backward  growth  of  the  hemispheres 
ceases  as  it  were,  but  in  the  higher  groups,  such  as  the  monkeys  and 
man,  they  grow  still  further  back,  until  they  completely  cover  in  the 
cerebellum,  so  that  on  looking  down  on  the  brain  from  above,  the  cere- 
bellum is  quite  concealed  from  view.  The  surface  of  the  hemispheres  is 
at  first  quite  smooth,  but  as  early  as  the  third  month  the  great  Sylvian 
fissure  begins  to  be  formed  (Fig.  446,  4). 

The  next  to  appear  is  the  parieto-occipital  or  perpendicular  fissure; 
these  two  great  fissures,  unlike  the  rest  of  the  sulci,  are  formed  by  a 
curving  round  of  the  whole  cerebral  mass. 

In  the  sixth  month  the  fissure  of  Eolando  appears:  from  this  time  till 
the  end  of  foetal  life  the  brain  grows  rapidly  in  size,  and  the  convolutions 
appear  in  quick  succession;  first  the  great  primary  ones  are  sketched  out, 
then  tlie  secondary,  and  lastly  the  tertiary  ones  in  the  sides  of  the  fissures. 
The  commissures  of  the  brain  (anterior,  middle,  and  posterior),  and  the 


GENERATIOlSr  AND  DEVELOPMENT.  291 

corpus  callosum,  are  developed  by  the  growth  of  fibres  across  the  middle 
line. 

The  Hippocampus  major  is  formed  by  the  folding  in  of  the  grey  mat- 
ter from  the  exterior  into  the  latter  ventricles.    The  essential  points  in 


Tig.  448.— Diagrammatic  horizontal  section  of  a  Vertebrate  brain.  The  figures  serve  both  for 
this  and  the  next  diagram.  Mb,  mid-brain:  what  lies  in  front  of  this  is  the  fore,  and  what  hes  be- 
hind, the  hind  brain;  i*,  lamina  terminaiis;  Oi/,  olfactory  lobes ;  JTmp,  hemispheres;  TH.E,thalam- 
encephalon;  Pn,,  pineal  gland;  Py,  pituitary  body;  FM,  foramen  of  Mvmro;  cs,  corpus  striatima; 
Th,  optic  thalamus;  CC,  cnu-a  cerebri:  the  mass  lying  above  the  canal  represents  the  corpora  quad- 
rigemina;  C6,  cerebellum;  I— IX,  the  nine  pairs  of  cranial  nerves;  1,  olfactory  ventricle;  2,  lateral 
ventricle;  3,  third  ventricle;  4,  fourth  ventricle;  + ,  iter  a  tertio  ad  quartum  ventriculum.  (Huxley.) 

the  structure  and  arrangement  of  the  various  parts  of  the  brain,  are  dia- 
grammatically  shown  in  the  two  accompanying  figures  (Figs.  448,  449). 

Development  of  the  Okgans  of  Sense. 

Eye. — Soon  after  the  first  three  cerebral  vesicles  have  become  distinct 
from  each  other,  the  anterior  one  sends  out  a  lateral  vesicle  from  each 
side  (primary  optic  vesicle),  which  grows  out  toward  the  free  surface,  its 
cavity  of  course  communicating  with  that  of  the  cerebral  vesicle  through 
the  canal  in  its  pedicle.  It  is  soon  met  and  invaginated  by  an  in-grow- 
ing process  from  the  epiblast  (Fig.  450),  very  much  as  the  growing 
tooth  is  met  by  the  process  of  epithelium  which  produces  the  enamel 
organ.  This  process  of  the  epiblast  is  at  first  a  depression  which  ulti- 
mately bcomes  closed  in  at  the  edges  so  as  to  produce  a  hollow  ball,  which 
is  thus  completely  severed  from  the  epithelium  with  which  it  was  origi- 
nally continuous.    From  this  hollow  ball  the  crystalline  lens  is  developed. 


292 


HAND-BOOK  OF  PHYSIOLOGY. 


By  the  ingrowth  of  the  lens  the  anterior  wall  of  the  primary  optic  vesicle 
is  forced  back  nearly  into  contact  with  the  posterior,  and  thus  the  primary 
optic  vesicle  is  almost  obliterated.    The  cells  in  the  anterior  wall  are 


Fig.  449.— Longitudinal  and  vertical  diagrammatic  section  of  a  Vertebrate  brain.  Letters  as  be- 
fore.  Lamina  terminalis  is  represented  by  the  strong  black  line  joining  Pn  and  By.  (Huxley.) 

much  longer  than  those  of  the  posterior  wall;  from  the  former  the  retina 
proper  is  developed,  from  the  latter  the  retinal  pigment. 

The  cup-shaped  hollow  in  which  the  lens  is  now  lodged  is  termed  the 
secondary  optic  vesicle:  its  walls  grow  up  all  round,  leaving,  however,  a 
slit  at  the  lower  part. 

Fig.  450.— Longitudinal  section  of  the  primary  optic  vesicle  in  the  chick  magnified  (from  Remak). 
— A,  from  an  embiyo  of  sixty-five  hours;  B,  a  few  hours  later;  C,  of  the  fourth  day;  c,  the  corneous 
layer  or  epidermis,  presenting  in  A,  the  open  depression  for  the  lens,  which  is  closed  in  B  and  C;  I, 
the  lens  follicle  and  lens;  pr,  the  primary  optic  vesicle;  in  A  and  B,  the  pedicle  is  shown;  in  C,  the 
section  being  to  the  side  of  the  pedicle,  the  latter  is  not  shown;  v,  the  secondary  ocular  vesicle  and 
vitreous  hmnor. 

Choroidal  Fissure. — Through  this  slit  (Fig.  452),  often  termed  the 
choroidal  fissure,  a  process  of  mesoblast  containing  numerous  blood-vessels 
projects,  and  occupies  the  cavity  of  the  secondary  optic  vesicle  behind 
the  lens,  filling  it  with  vitreous  humor  and  furnishing  the  lens  capsule 
and  the  capsulo-pupillary  membrane.  This  process  in  Mammals  projects, 
not  only  into  the  secondary  optic  vesicle,  but  also  into  the  pedicle  of  the 
primary  optic  vesicle  invaginating  it  for  some  distance  from  beneatli, 
and  thus  carrying  up  the  arteria  centralis  retincB  into  its  permanent  posi- 
tion in  the  centre  of  the  optic  nerve. 

This  invagination  of  the  optic  nerve  docs  not  occur  in  birds,  and  con- 
sequently no  arteria  centralis  retinae  exists  in  them.  But  they  possess 
an  important  permanent  relic  of  the  original  protrusion  of  the  mesoblast 
through  the  choroidal  fissure,  forming  tlie  pecten,  wliile  a  remnant  of  the 


GENERATION  AND  DEVELOPMENT. 


293 


same  fissure  sometimes  occurs  in  man  under  the  name  coloboma  iridis. 
The  cavity  of  the  primary  optic  vesicle  becomes  completely  obliterated, 
and  the  rods  and  cones  come  into  apposition  with  the  pigment  layer  of 
the  retina.  The  cavity  of  its  pedicle  disappears  and  the  solid  optic  nerve 
is  formed.  Meanwhile  the  cavity  which  existed  in  the  centre  of  the 
primitive  lens  becomes  filled,  up  by  the  growth  of  fibres  from  its  posterior 
wall.    The  epithelium  of  the  cornea  is  developed  from  the  epiblast,  while 


Fig.  451.  Fig.  452. 

Fig.  451.— Diagrammatic  sketch  of  a  vertical  longitudinal  section  through  the  eyeball  of  a  human 
foetus  of  four  weeks.  The  section  is  a  little  to  the  side,  so  as  to  avoid  passing  through  the  ocular 
cleft;  c,  the  cuticle  where  it  becomes  later  the  corneal  epithelium;  Z,  the  lens;  op,  optic  nerve  formed 
by  the  pedicle  of  the  primary  optic  vesicle;  vp^  primary  medullary  cavity  or  optic  vesicle;  p,  the 
pigment  layer  of  the  retina;  r,  the  inner  wall  forming  the  retina  proper;  vs,  secondary  optic  vesicle 
containing  the  rudiment  of  the  vitreous  humor,    x  100.  (Kolliker.) 

Fig.  452.— Transverse  vertical  section  of  the  eyeball  of  a  human  embryo  of  four  weeks.  The  an- 
terior half  of  the  section  is  represented;  pr^  the  remains  of  the  cavity  of  the  primary  optic  vesicle; 
33,  the  inner  part  of  the  outer  layer  forming  the  retinal  pigment;  r,  the  thickened  inner  part  giving 
rise  to  the  columnar  and  other  structures  of  the  retina;  v,  the  commencing  vitreous  humor  within 
the  secondary  optic  vesicle;  v\  the  ocular  cleft  through  which  the  loop  of  the  central  blood-vessel, 
0,  projects  from  below;  I,  the  lens  with  a  central  cavity,    x  100.  (Kolliker.) 


the  corneal  tissue  proper  is  derived  from  the  mesoblast  which  intervenes 
between  the  epiblast  and  the  primitive  lens  which  was  originally  continu- 
ous with  it.  The  sclerotic  coat  is  developed  round  the  eyeball  from  the 
general  mesoblast  in  which  it  is  imbedded. 

The  iris  is  formed  rather  late,  as  a  circular  septum  projecting  inward, 
from  the  fore  part  of  the  choroid,  between  the  lens  and  the  cornea.  In 
the  eye  of  the  foetus  of  Mammalia,  the  pupil  is  closed  by  a  delicate  mem- 
brane, the  memhrana  jmpillaris,  which  forms  the  front  portion  of  a 
highly  vascular  membrane  that,  in  the  foetus,  surrounds  the  lens,  and  is 
named  the  memlrana  capsulo-pupillaris  (Fig.  453).  It  is  supplied  with 
blood  by  a  branch  of  the  arteria  centralis  retinm,  which,  passing  forward 
to  the  back  of  the  lens,  there  subdivides.  The  membrana  capsulo-pupil- 
laris  withers  and  disappears  in  the  human  subject  a  short  time  before 
birth. 

The  eyelids  of  the  human  subject  and  mammiferous  animals,  like  those 
of  birds,  are  first  developed  in  the  form  of  a  ring.  They  then  extend 
over  the  globe  of  the  eye  until  they  meet  and  become  firmly  agglutinated 


294 


IIAA^D-BOOK  OF  PHYSIOLOGY. 


to  each  other.  But  before  birth,  or  in  the  Carnivora  after  birth,  they 
again  separate. 

Ear. — Very  early  in  the  development  of  the  embryo  a  depression 
or  ingrowth  of  the  epiblast  occurs  on  each  side  of  the  head  which  deepens 
and  soon  becomes  a  closed  follicle.  This  pmnary  otic  vesicle,  which  closely 
corresponds  in  its  formation  to  the  lens  follicle  in  the  eye,  sinks  down 
to  some  distance  from  the  free  surface;  from  it  are  developed  the  epithe- 
lial lining  of  the  memhranous  labyrinth  of  the  internal  ear,  consisting  of 
the  vestibule  and  its  semicircular  canals  and  the  scala  media  of  the 
cochlea.  The  surrounding  mesoblast  gives  rise  to  the  various  fibrous 
bony  and  cartilaginous  parts  which  complete  and  enclose  this  membran- 
ous labyrinth,  the  bony  semicircular  canals,  the  w^alls  of  the  cochlea  with 


Fig.  453.— Blood-vessels  of  the  eapsulo-pupillary  membrane  of  a  new-bom  kitten,  magnified.  The 
drawing  is  taken  from  a  preparation  injected  by  Tierseh,  and  shows  in  the  central  part  the  converg- 
ence of  the  network  of  vessels  in  the  pupillary  membrane.  (Kolliker.) 

its  scala  vestibuli  and  scala  tympani.  In  the  mesoblast,  between  the 
primary  otic  vesicle  and  the  brain,  the  auditory  nerve  is  gradually  differ- 
entiated and  forms  its  central  and  peripheral  attachments  to  the  brain 
and  internal  ear  respectively.  According  to  some  authorities,  however, 
it  is  said  to  take  its  origin  from  and  grow  out  of  the  hind  brain. 

The  Eustachian  tube,  the  cavity  of  the  tympanum,  and  the  external 
auditory  passage,  are  remains  of  the  first  branchial  cleft.  The  membrana 
tympani  divides  the  cavity  of  this  cleft  into  an  internal  space,  the  tym- 
panum and  the  external  meatus.  The  mucous  membrane  of  the  mouth, 
which  is  prolonged  in  the  form  of  a  diverticulum  through  the  Eustachian 
tube  into  the  tympanum,  and  the  external  cutaneous  system,  come  into 
relation  witli  each  otlier  at  this  point;  the  two  membranes  being  sepa- 
rated only  by  the  proper  membrane  of  the  tympanum. 

The  pinna  or  external  ear  is  developed  from  a  process  of  integument 
in  the  neighborhood  of  the  first  and  second  visceral  arclies,  and  probably 
corresponds  to  the  gill-cover  (operculum)  in  fishes. 


GENERATIOK  AND  DEVELOPMENT. 


295 


Nose. — The  nose  originates  like  the  eye  and  ear  in  a  depression  of 
the  superficial  epiblast  at  each  side  of  the  fronto-nasal  process  (primary 
olfactory  groove),  which  is  at  first  completely  separated  from  the  cavity 
of  the  mouth,  and  gradually  extends  backward  and  downward  till  it 
opens  into  the  mouth. 

The  outer  angles  of  the  fronto-nasal  process,  uniting  with  the  maxil- 
lary process  on  each  side,  convert  what  was  at  first  a  groove  into  a  closed 
canal. 

Developmei^t  of  the  Alimentaky  Canal. 

The  alimentary  canal  in  the  earliest  stages  of  its  development  consists 
of  three  distinct  parts — the  fore  and  hind  gut  ending  blindly  at  each  end 
of  the  body,  and  a  middle  segment  which  communicates  freely  on  its 


A  B  0 


Fig.  454.— Outlines  of  the  form  and  position  of  the  aUmentary  canal  in  successive  stages  of  its 
developnaent.  A,  alimentary  canal,  etc.,  in  an  embryo  of  four  weeks;  B,  at  six  weeks;  C,  at  eight 
weeks;  D,  at  ten  weeks;  I,  the  primitive  lungs  connected  with  the  pharynx;  s,  the  stomach;  d,  the 
duodenum;  i,  the  small  intestine;  i',  the  large;  c,  the  caecum  and  vermiform  appendage;  r,  the  rec- 
tum; cl,  in  A,  the  cloaca;  a,  in  B,  the  anus  distinct  from  s  i,  the  sinus  uro-genitalis;  v,  the  yelk-sac; 
vi,  the  vitello-intestinal  duct;  u,  the  urinary  bladder  and  urachus  leading  to  the  allantois;  (/,  genital 
ducts.   (Allen  Thomson.) 

ventral  surface  with  the  cavity  of  the  yelk- sac  through  the  vitelline  or 
omphalo-mesenteric  duct  (p.  261,  Vol.  II.). 

From  the  fore-gut  are  formed  the  pharynx,  oesophagus,  and  stomach; 
from  the  hind-gut,  the  lower  end  of  the  colon  and  the  rectum.  The 
mouth  is  developed  by  an  involution  of  the  epiblast  between  the  maxillary 
and  mandibular  processes,  which  becomes  deeper  and  deeper  till  it  reaches 
the  blind  end  of  the  fore-gut,  and.  at  length  communicates  freely  with 
the  pharynx  by  the  absorption  of  the  partition  between  the  two. 

At  the  other  end  of  the  alimentary  canal  the  anus  is  formed  in  a 


296 


H^ND-BOOK  OF  PHYSIOLOGY. 


precisely  similar  way  by  an  involution  from  the  free  surface,  which  at 
length  opens  into  the  hind-gut.  When  the  depression  from  the  free  sur- 
face does  not  reach  the  intestine,  the  condition  known  as  imperforate 
anus  results.  A  similar  condition  may  exist  at  the  other  end  of  the 
alimentary  canal  from  the  failure  of  the  involution  which  forms  the 


Fig.  455.— First  appearance  of  the  parotid  gland  in  the  embryo  of  a  sheep. 

mouth,  to  meet  the  fore-gut.  The  middle  portion  of  the  digestive  canal 
becomes  more  and  more  closed  in  till  its  originally  wide  communication 
with  the  yelk-sac  becomes  narrowed  down  to  a  small  duct  (vitelline). 
This  duct  usually  completely  disappears  in  the  adult,  but  occasionally  the 


Fig.  456.— Lobules  of  the  parotid,  with  the  saUvary  ducts,  in  the  embryo  of  the  sheep  at  a  more 
advanced  sta^e. 

proximal  portion  remains  as  a  diverticulum  from  the  intestine.  Some- 
times a  fibrous  cord  attaching  some  part  of  the  intestine  to  the  umbilicus, 
remains  to  represent  the  vitelline  duct.  Such  a  cord  has  been  known 
to  cause  in  after-life  strangulation  of  the  bowel  and  death. 


GENERATION  AND  DEVELOPMENT. 


297 


The  alimentary  canal  lies  in  the  form  of  a  straight  tube  close  beneath 
the  vertebral  column,  but  it  gradually  becomes  divided  into  its  special 
parts,  stomach,  small  intestine,  and  large  intestine  (Fig.  454),  and  at  the 
same  time  comes  to  be  suspended  in  the  abdominal  cavity  by  means  of  a 
lengthening  mesentery  formed  from  the  splanchnopleure  which  attaches 
it  to  the  vertebral  column.  The  stomach  originally  has  the  same  direction 
as  the  rest  of  the  canal;  its  cardiac  extremity  being  superior,  its  pylorus 
inferior.  The  changes  of  position  which  the  alimentary  canal  undergoes 
may  be  readily  gathered  from  the  accompanying  figures  (Fig.  454'). 

Pancreas  and  Salivary  Glands. — The  principal  glands  in  connec- 
tion with  the  intestinal  canal  are  the  salivary,  pancreas,  and  the  liver. 
In  Mammalia,  each  salivary  gland  first  appears  as  a  simple  canal  with 
bud-like  processes  (Fig.  455)^  lying  in  a  gelatinous  nidus  or  blastema, 


Fig.  457.— Diagram  of  part  of  digestive  tract  of  a  chick  (fourth  day).  The  black  line  represents 
hypoblast,  the  outer  shading  mesoblast:  I  g,  lung  diverticulum,  with  expanded  end  forming  primary 
lung- vesicle;  S  f,  stomach;  I,  two  hepatic  diverticida,  with  their  terminations  united  by  solid  rows  of 
hypoblast  cells;  p,  diverticulum  of  the  pancreas  with  the  vesicular  diverticida  coming  from  it. 
(Gotte.) 

Fig.  458. — Rudiments  of  the  liver  on  the  intestine  of  a  chick  at  the  fifth  day  of  incubation.  1, 
heart;  2,  intestine;  3,  diverticulum  of  the  intestine  in  which  the  liver  (4)  is  developed;  5,  part  of  the 
mucous  layer  of  the  germinal  membrane.  (Miiller.) 


and  communicating  with  the  cavity  of  the  mouth.  As  the  development 
of  the  gland  advances,  the  canal  becomes  more  and  more  ramified,  in- 
creasing at  the  expense  of  the  blastema  in  which  it  is  still  enclosed.  The 
branches  or  salivary  ducts  constitute  an  independent  system  of  closed 
tubes  (Fig.  456).  The  pancreas  is  developed  exactly  as  the  salivary 
glands,  but  is  developed  from  the  hypoblast  lining  the  intestine,  while 
the  salivary  glands  are  formed  from  the  epiblast  lining  the  mouth. 

Liver. — The  liver  is  developed  by  the  protrusion,  as  it  were,  of  a  part 
of  the  walls  of  the  intestinal  canal,  in  the  form  of  two  conical  hollow 
branches  which  embrace  the  common  venous  stem  (Figs.  457,  458).  The 
outer  part  of  these  cones  involves  the  omphalo-mesenteric  vein,  which 
breaks  up  in  its  interior  into  a  plexus  of  capillaries,  ending  in  venous 


Fig.  457. 


Fig.  458. 


298 


HAND-BOOK  OF  PHYSIOLOGY. 


trunks  for  the  conveyance  of  the  blood  to  the  heart.  The  inner  portion 
of  the  cones  consists  of  a  number  of  solid  cylindrical  masses  of  cells, 
derived  probably  from  the  hypoblast,  which  become  gradually  hollowed 
by  the  formation  of  the  hepatic  ducts,  and  among  which  blood-vessels 
are  rapidly  developed.  The  gland-cells  of  the  organs  are  derived  from 
the  hypoblast,  the  connective  tissue  and  vessels  without  doubt  from  the 
mesoblast.  The  gall-bladder  is  developed  as  a  diverticulum  from  the 
hepatic  duct.  The  spleen,  lymphatic,  and  thymus  glands  are  developed 
from  tho  mesoblast:  the  thyroid  partly  also  from  the  hypoblast  which 
grows  into  it  as  a  divei-ticulum  from  the  fore-gut. 

Development  of  the  Eespiratory  Apparatus. 

The  lungs,  at  their  first  development,  appear  as  small  tubercles  or 
diverticular  from  the  abdominal  surface  of  the  oesophagus. 

The  two  diverticular  at  first  open  directly  into  the  oesophagus,  but 
as  they  grow,  a  separate  tube  (the  future  trachea)  is  formed  at  their  point 
of  fusion,  opening  into  the  oesophagus  on  its  anterior  surface.  These 

Fig.  459  illustrates  the  development  of  the  respiratory  organs,  a,  is  the  oesophagus  of  a  chick 
on  the  fourth  day  of  incubation,  with  the  rudiments  of  the  trachea  on  the  lung  of  the  left  side,  viewed 
laterally;  1,  the  inferior  wall  of  the  oesophagus;  2,  the  upper  wall  of  the  same  tube;  3,  the  rudiment- 
ary lung;  4,  the  stomach,  b,  is  the  same  object  seen  from  below,  so  that  both  lungs  are  visible,  c, 
shows  the  tongue  and  respiratory  organs  of  the  embryo  of  a  horse:  1,  the  tongue;  2,  the  larynx;  3, 
the  trachea;  4,  the  lungs,  viewed  from  the  upper  side.   (After  Rathke.) 

primary  diverticula  of  the  hypoblast  of  the  alimentary  canal  send  off 
secondary  branches  into  the  surrounding  mesoblast,  and  these  again  give 
off  tertiary  branches,  forming  the  air-cells.  Thus  we  have  the  lungs 
formed:  the  epithelium  lining  their  air-cells,  bronchi,  and  trachea  being 
derived  from  the  hypoblast,  and  all  the  rest  of  the  lung-tissue,  nerves, 
lymphatics,  and  blood-vessels,  cartilaginous  rings,  and  muscular  fibres  of 
the  bronchi  from  the  mesoblast.    The  diaphragm  is  early  developed. 

The  Wolffian  Bodies,  Urinary  Apparatus,  and  Sexual  Organs. 

The  Wolffian  bodies  are  organs  peculiar  to  the  embryonic  state,  and 
may  be  regarded  as  temporary,  rather  than  rndinicntal,  kidneys;  for 
although  they  seem  to  discharge  the  functions  of  these  latter  organs,  they 
are  not  developed  into  them. 


GENERATION  AND  DEVELOPMENT. 


299 


Appearance  of  First  Rudiments. — The  Wolffian  duct  makes  its  ap- 
pearance at  an  early  stage  in  the  history  of  the  embryo,  as  a  cord  running 
longitudinally  on  each  side  in  the  mass  of  mesoblast,  which  lies  just  ex- 
ternal to  the  protovertebras  (ung,  Fig.  460).  This  cord,  at  first  solid, 
becomes  gradually  hollowed  out  to  form  a  tube  (Wolffian  duct)  which 
sinks  down  till  it  projects  beneath  the  lining  membrane  into  the  pleuro- 
peritoneal  cavity. 

The  primitive  tube  thus  formed  sends  off  secondary  diverticula  at  fre- 
quent intervals  which  grow  into  the  surrounding  mesoblast:  tufts  of  ves- 
sels grow  into  the  blind  ends  of  these  tubes,  invaginating  them  and  pro- 
ducing ^'Malpighian  bodies'^  very  similar  in  appearance  to  those  of  the 
permanent  kidney,  which  constitute  the  substance  of  the  Wolffian  body. 


Fig.  460.— Transverse  of  embryo  chick  (third  day),  m  r,  rudimentary  spinal  cord;  the  primitive 
central  canal  has  become  constricted  in  the  middle;  c/i,  notochord;  uwh,  primordial  vertebral  mass; 
m,  muscle-plate;  dr,  d/,  hypoblast  and  visceral!  ay  er  of  mesoblast  lining  groove,  which  is  not  yet 
closed  in  to  form  the  intestines;  ao,  one  cf  the  primitive  aortse;  un,  Wolffian  body;  ung^  Wolffian 
duct;  vc,  vena  cardinalis;  h,  epiblast;  h  p,  somatopleure  and  its  reflection  to  form  a/,  amniotic 
fold;  p,  pleuro-peritoneal  cavity.  (Kolliker.) 

Meanwhile  another  portion  of  mesoblast  between  the  Wolffian  body  and 
the  mesentery  projects  in  the  form  of  a  ridge,  covered  on  its  free  surface 
with  epithelium  termed  **germ  epithelium.^'  From  this  projection  is 
developed  the  reproductive  gland  (ovary  or  testis  as  the  case  may  be). 

Simultaneously,  on  the  outer  wall  of  the  Wolffian  body,  between  it 
and  the  body- wall  on  each  side,  an  involution  is  formed  from  the  pleuro- 
peritoneal  cavity  in  the  form  of  a  longitudinal  furrow,  whose  edges  soon 
close  over  to  form  a  duct  (Miiller's  duct). 

All  the  above  points  are  shown  in  the  accompanying  figures,  460,  461,  • 
462,  463. 

The  Wolffian  bodies,  or  temporary  kidneys,  as  they  may  be  termed, 
give  place  at  an  early  period  in  the  human  foetus  to  their  successors,  the 
permanent  kidneys,  which  are  developed  behind  them.  They  diminish 
rapidly  in  size,  and  by  the  end  of  the  third  month  have  almost  entirely 
disappeared.    In  connection,  however,  with  their  upper  part,  in  the  male. 


300 


HAJSTD-BOOK  OF  PHYSIOLOGY. 


there  are  developed  from  a  new  mass  of  blastema,  the  vasa  efferentia, 
coni  vasculosis  and  globus  major  of  the  epididj'mis;  and  thus  is  brought 
about  a  direct  connection  between  the  secreting  part  of  the  testicle  and 
its  duct  (Cleland,  Banks).  The  "Wolffian  ducts  persist  in  the  male,  and 
are  developed  to  form  the  body  and  globus  minor  of  the  epididymis,  the 
vas  deferens,  and  ejaculatory  duct  on  each  side,  the  vesiculai  seminales 
forming  diverticula  from  their  lower  part.  In  the  female  a  small  relic 
of  the  "Wolffian  body  persists  as  the  ''parovarium^^;  in  the  male  a  similar 
relic  is  termed  the  "organ  of  Giraldes.'^  The  lower  end  of  the  Wolffian 
duct  remains  in  the  female  as  the  "duct  of  G-aertner/^  which  descends 
toward,  and  is  lost  upon,  the  anterior  wall  of  the  vagina. 


Fig.  461.— Section  of  intermediate  ceU-mass  on  the  fourth  day.  7??.  mesentery:  L,  somatopleure; 
a',  germinal  epithelium,  from  which  z.  the  duct  of  Miiller.  becomes  involuted:  a.  thickened  part  of 

f:erminal  epithelium  in  which  the  primitive  ova  C  and  o.  are  lying;  E.  modified  mesoblast.  wlueh  will 
orm  the  stroma  of  the  ovarj-;  WK,  Wollitian  hody;  y,  WolMan  duct:  x  lt50.  (,Walde3-er.) 

From  the  lower  end  of  the  Wolffian  duct  a  diverticulum  grows  back 
along  the  body  of  the  embryo  toward  its  anterior  extremity,  and  ulti- 
mately forms  the  ureter.  Secondary  diverticula  are  given  oif  from  it  and 
grow  into  the  surrounding  blastema  of  blood-vessels  and  cells. 

Malpighian  bodies  are  formed  just  as  in  the  Wolffian  body,  by  the 
invagination  of  the  blind  knobbed  end  of  these  diverticula  by  a  tuft  of 
vessels  (Fig.  4G3).  Tliis  2)rocess  is  precisely  similar  to  the  invagination 
of  the  primary  optic  vesicle  by  the  rudimentary  lens.  Thus  tlie  kidney 
is  devel()])cd,  consisting  at  first  of  a  number  of  separate  lohides:  this  con- 
dition remaining  throughout  life  in  many  of  the  lower  animals,  e.g., 


GENERATION  AND  DEVELOPMENT. 


seals  and  whales,  and  traces  of  this  lobulation  being  visible  in  the  human 
foetus  at  birth.  In  the  adult  all  the  lobules  are  fused  into  a  compact 
solid  organ. 


Fig.  462.— Diagrams  showing  the  relations  of  the  female  (the  left-hand  figure  o)  and  of  the  male 

(the  right-hand  figure  o )  reproductive  organs  to  the  general  plan  (the  middle  figure)  of  these  organs 
in  the  higher  vertebrata  (including  man).    CZ,  cloaca;  i?,  rectvun;  5  Z,  urinary  bladder;  U,  lu-eter; 

kidney;  Uh,  urethra;  genital  gland,  ovary  or  testis;  W,  Wolffian  body;  W Wolffian  duct; 
M,  Miillerian  duct;  Pst,  prostate  gland;  Cp,  Cowper's  gland;  Csp,  corpus  spongiosiun;  C  c,  cor- 
pus cavernosimi. 

In  the  female.— V,  vagina;  Ut,  uterus;  Fp,  Fallopian  tube;  G  t,  Gaertner's  duct;  Pv,  parova- 
rium; A,  anus;  C  c,  Csp,  cUtoris. 

In  the  male.— C  s p,  C  c,  Items;  Ut,  uterus  masculinus;  Fs,  vesicula  seminalis;  Vd,\as  defer- 
ens. (Huxley.) 


a 


Fig.  463.— Transverse  section  of  a  developing  Malpighian  capsule  and  tuft  (human).  From  a 
foetus  at  about  the  fourth  month;  a,  flattened  cells  growing  to  form  the  capsule;  6,  more  rounded 
cells,  continuous  with  the  above,  reflected  round  c,  and  finally  enveloping  it;  c,  mass  of  embryonic 
cells  which  will  later  become  developed  into  blood-vessels.    X  300.   (W.  Pye.) 


The  supra-renal  capsules  originate  in  a  mass  of  mesoblast  just  above 
the  kidneys;  soon  after  their  first  appearance  they  are  very  much  larger 


HAND-BOOK  OF  PHYSIOLOGY. 


than  the  kidneys  (see  Fig.  464),  but  by  the  more  rapid  growth  of  the 
latter  this  relation  is  soon  reversed. 


Latee  Development. 

The  first  appearance  of  the  generative  gland  has  -been  already  de- 
scribed: for  some  time  it  is  impossible  to  determine  whether  an  ovary  or 
testis  will  be  developed  from  it;  gradually  however  the  special  characters 
belonging  to  one  of  them  appear,  and  in  either  case  the  organ  soon  be- 
gins to  assume  a  relatively  lower  position  in  the  body;  the  ovaries  being 
ultimately  placed  in  the  pelvis;  while  toward  the  end  of  foetal  existence 
the  testicles  descend  into  the  scrotum,  the  testicle  entering  the  internal 
inguinal  ring  in  the  seventh  month  of  foetal  life,  and  completing  its 
descent  through  the  inguinal  canal  and  external  ring  into  the  scrotum  by 
the  end  of  the  eighth  month.  A  pouch  of  peritoneum,  the  processus 
vaginalis,  precedes  it  in  its  descent,  and  ultimately  forms  the  tunica 
vaginalis  or  serous  covering  of  the  organ;  the  communication  between  the 
tunica  vaginalis  and  the  cavity  of  the  peritoneum  being  closed  only  a 
short  time  before  birth.  In  its  descent,  the  testicle  or  ovary  of  course 
retains  the  blood-vessels,  nerves,  and  lymphatics,  which  were  supplied  to 
it  while  in  the  lumbar  region,  and  which  are  compelled  to  follow  it,  so  to 
speak,  as  it  assumes  a  lower  position  in  the  body.  Hence  the  explanation 
of  the  otherwise  strange  fact  of  the  origin  of  these  parts  at  so  consider- 
able a  distance  from  the  organ  to  which  they  are  distributed. 

Descent  of  the  Testicles  into  Scrotum. — The  means  by  which 
the  descent  of  the  testicles  into  the  scrotum  is  effected  are  not  fully  and 
exactly  known.  It  was  formerly  believed  that  a  membranous  and  partly 
muscular  cord,  called  the  guhernaculum  testis,  which  extends  while  the 
testicle  is  yet  high  in  the  abdomen,  from  its  lower  part,  through  the  ab- 
dominal wall  (in  the  situation  of  the  inguinal  canal)  to  the  front  of  the 
pubes  and  lower  part  of  the  scrotum,  was  the  agent  by  the  contraction  of 
which  the  descent  was  effected.  It  is  now  generally  believed,  however, 
that  such  is  not  the  case;  and  that  the  descent  of  the  testicle  and  ovary 
is  rather  the  result  of  a  general  process  of  development  in  these  and 
neighboring  parts,  the  tendency  of  which  is  to  produce  this  change  in  the 
relative  position  of  these  organs.  In  other  words,  the  descent  is  not  the 
result  of  a  mere  mechanical  action,  by  wliich  the  organ  is  dragged  down 
to  a  lower  position,  but  rather  one  change  out  of  many  which  attend  the 
gradual  development  and  re-arrangement  of  these  organs.  It  may  be 
repeated,  however,  that  the  details  of  the  process  by  which  the  descent 
of  the  testicle  into  tlie  scrotum  is  effected  arc  not  accurately  known. 

The  homologue,  in  tlie  female,  of  tlie  gubernaculum  testis,  is  a  struc- 
ture called  the  round  lifiauvnit  of  llie  uterus,  which  extends  through  the 


GENERATION  AND  DEVELOPMENT. 


308 


inguinal  canal,  from  the  outer  and  upper  part  of  the  uterus  to  the  subcu- 
taneous tissue  in  front  of  the  symphysis  pubis. 

At  a  very  early  stage  of  foetal  life,  the  Wolffian  ducts,  ureters,  and 
Miillerian  ducts,  open  into  a  receptacle  formed  by  the  lower  end  of  the 
allantois,  or  rudimentary  bladder;  and  as  this  communicates  with  the 
lower  extremity  of  the  intestine,  there  is  for  the  time  a  common  recep- 
tacle or  cloaca  for  all  these  parts,  which  opens  to  the  exterior  of  the  body 
through  a  part  corresponding  with  the  future  anus,  an  arrangement 
which  is  permanent  in  Reptiles,  Birds,  and  some  of  the  lower  Mammalia. 


Fig.  464'.— Diagram  of  the  Wolffian  bodies,  Mullerian  ducts  and  adjacent  parts  previous  to  sexual 
distinction,  as  seen  from  before,  s  r,  the  supra-renal  bodies;  r,  the  kidneys;  o  t,  conamon  blastema 
of  ovaries  or  testicles;  W,  Wolffian  bodies;  w.  Wolffian  ducts;  m,  m,  Miillerian  ducts;  g  c,  genital 
cord;  u  g,  sinus  m-ogenitaUs;  i,  intestine;  c  I,  cloaca.   (Allen  Thomson.) 


In  the  human  foetus,  however,  the  intestinal  portion  of  the  cloaca  is  cut 
off  from  that  which  belongs  to  the  urinary  and  generative  organs;  a  sepa- 
rate passage  or  canal  to  the  exterior  of  the  body,  belonging  to  these  parts, 
being  called  the  sinus  urogenitalis.  Subsequently,  this  canal  is  divided, 
by  a  process  of  division  extending  from  before  backward  or  from  above 
downward,  into  a  **pars  urinaria"  and  a  ''pars  genitalis."  The  former, 
continuous  with  the  uraclms,  is  converted  into  the  urinary  bladder. 

The  Fallopian  tubes,  the  uterus,  and  the  vagina  are  developed  from 
the  Mullerian  ducts  (Fig.  464,  m,  and  Fig.  465)  whose  first  appearance 
has  been  already  described.  The  two  Mullerian  ducts  are  united  below 
into  a  single  cord,  called  the  genital  cord,  and  from  this  are  developed 


304 


HAND-BOOK  OF  PHYSIOLOGY. 


the  Yagina,  as  well  as  tlie  cervix  and  the  lower  portion  of  the  body  of  the 
uterus;  while  the  ununited  portion  of  the  duct  on  each  side  forms  the 
upper  part  of  the  uterus,  and  the  Fallopian  tube.  In  certain  cases  of 
arrested  or  abnormal  development,  these  portions  of  the  Miillerian  ducts 
may  not  become  fused  together  at  their  lower  extremities,  and  there  is 
left  a  cleft  or  horned  condition  of  the  upper  part  of  the  uterus  resembling 
a  condition  which  is  permanent  in  certain  of  the  lower  animals. 

In  the  male,  the  Miillerian  ducts  have  no  special  function,  and  are 
but  slightly  developed.  The  hydatid  of  Morgagni  is  the  remnant  of  the 
upper  part  of  the  Miillerian  duct.    The  small  prostatic  pouch,  uterus 


6 


Urinary  and  generative  organs  of  a  human  female  embryo,  measuring  m  inches  in  length. 

Fig.  465.— a.  Greneral  view  of  these  parts:  1,  supra-renal  capsules;  2,  kidneys;  3,  ovary;  4,  Fal- 
lopian tube;  5,  uterus;  6,  intestine;  7,  the  bladder. 

B.— Bladder  and  Generative  organs  of  the  same  embryo  viewed  from  the  side:  a,  the  urinary 
bladder  (at  the  upper  part  is  a  portion  of  the  urachus);  2,  m-ethra;  3,  uterus  (with  two  cornua);  4, 
vagina;  5,  part  as  yet  common  to  the  vagina  and  urethra;  6,  common  orifice  of  the  urinary  and  gen- 
erative organs ;  7,  the  clitoris. 

C— Internal  generative  organs  of  the  same  embryo:  1,  the  uterus;  2,  the  round  ligaments;  3, 
the  Fallopian  tubes  (formed  by  the  Miillerian  ducts);  4,  the  ovaries;  5,  the  remains  of  the  Wolffian 
bodies. 

D.— External  generative  organs  of  the  same  embryo:  1,  the  labia  majora;  2,  the  njTnphae;  3, 
clitoris;  4,  anus.  (Miiller.) 

mascuUnus,  or  sinus  pocularis,  forms  the  atrophied  remnant  of  the  dis- 
tal end  of  the  genital  cord,  and  is,  of  course,  therefore,  the  homologue, 
in  the  male,  of  the  vagina  and  uterus  in  the  female. 

The  external  parts  of  generation  are  at  first  the  same  in  both  sexes. 
The  opening  of  the  genito-urinary  apparatus  is,  in  both  sexes,  bounded 
by  two  folds  of  skin,  whilst  in  front  of  it  there  is  formed  a  penis-like  body 


GENERATION  AND  DEVELO:PMENT. 


305 


surmounted  by  a  glans,  and  cleft  or  furrowed  along  its  under  surface. 
Tlie  borders  of  the  furrows  diverge  posteriorly,  running  at  the  sides  of 
the  genito- urinary  orifice  internally  to  the  cutaneous  folds  just  mentioned 
(see  Figs.  465,  466,  467).  In  the  female,  this  body  becoming  retracted, 
forms  the  clitoris,  and  the  margins  of  the  furrow  on  its  under  surface  are 
converted  into  the  nymphse,  or  labia  minora,  the  labia  majora  pudendae 
being  constituted  by  the  great  cutaneous  folds.  In  the  male  foetus,  the 
margins  of  the  furrow  at  the  under  surface  of  the  penis  unite  at  about  the 
fourteenth  week,  and  form  that  part  of  the  urethra  which  is  included  in 
the  penis.  The  large  cutaneous  folds  form  the  scrotum,  and  later  (in  the 
eighth  month  of  development),  receive  the  testicles,  which  descend  into 
them  from  the  abdominal  cavity.  Sometimes  the  urethra  is  not  closed, 
and  the  deformity  called  hypospadias  then  results.  The  appearance  of 
hermaphroditism  may,  in  these  cases,  be  increased  by  the  retention  of  the 
testes  within  the  abdomen. 


Vol.  11.-20. 


CHAPTER  XXI. 


ON  THE  RELATION  OF  LIFE  TO  OTHER  FORCES. 

An"  enumeration  of  theories  concerning  the  nature  of  life  would  b& 
beside  the  purpose  of  the  present  chapter.  They  are  interesting  as  marks 
of  the  way  in  which  various  minds  have  been  influenced  by  the  mystery 
wnich  has  always  hung  about  vitality;  their  destruction  is  but  another 
warning  that  any  theory  we  can  frame  must  be  considered  only  a  tie  for 
connecting  present  facts,  and  one  that  must  yield  or  break  on  any  addi- 
tion to  the  number  which  it  is  to  bind  together. 

Before  attention  had  been  drawn  to  the  mutual  convertibility  of  the 
various  so-called  physical  forces — heat,  light,  electricity,  and  others — and 
until  it  had  been  shown  that  these,  like  the  matter  through  which  they 
act,  are  limited  in  amount,  and  strictly  measurable;  that  a  given  quantity 
of  one  force  can  produce  a  certain  quantity  of  another  and  no  more;  that 
a  given  quantity  of  combustible  material  can  produce  only  a  given  quan- 
tity of  steam,  and  this  again  only  so  much  motive-power;  it  was  natural 
that  men's  minds  should  be  satisfied  with  the  thought  that  vital  force 
was  some  peculiar  innate  power,  unlimited  by  matter,  and  altogether  in- 
dependent of  structure  and  organization.  The  comparison  of  life  to  a 
flame  is  probably  as  early  as  any  thought  about  life  at  all.  And  so  long- 
as  light  and  heat  were  thought  to  be  inherent  qualities  of  certain  material 
which  perished  utterly  in  their  production,  it  is  not  strange  that  life 
also  should  have  been  reckoned  some  strange  spirit,  pent  up  in  the 
germ,  expending  itself  in  growth  and  development,  and  finally  declining 
and  perishing  with  the  body  which  it  had  inhabited. 

With  the  recognition,  however,  of  a  distinct  correlation  between  the 
physical  forces,  came  as  a  natural  consequence  a  revolution  of  the  com- 
monly accepted  theories  concerning  life  also.  The  dictum,  so  long  ac- 
cepted, that  life  was  essentially  independent  of  physical  force  beffan  to 
be  questioned. 

As  it  is  well-nigh  impossible  to  give  a  definition  of  life  that  shall  be 
sliort,  comprehensive,  and  intelligible,  it  will  be  best,  perhaps,  to  take  its 
chief  manifcstjitions,  and  see  how  far  these  seem  to  be  dependent  on 
other  forces  in  nature,  and  how  connected  with  them. 


'  This  chapter  is  a  reprint,  with  some  verbal  alterations,  of  an  essay  contributed  to 
Si.  Bartholonu'w'ff  Hospital  lleports,  18G7,  by  AV.  Morrant  Baker 


THE  RELATION  OF  LIFE  TO  OTHER  FORCES. 


307 


Life  manifests  itself  by  Birth,  Growth,  Development,  Decline  and 
Death;  and  an  idea  of  life  will  most  naturally  arise  by  taking  these  events 
in  succession,  and  studying  them  individually,  and  in  relation  to  each 
other. 

When  the  embryo  in  a  seed  awakes  from  that  state,  neither  life  nor 
death,  which  is  called  dormant  vitality,  and,  bursting  its  envelopes, 
begins  to  grow  up  and  develop,  it  may  be  said  that  there  is  a  birth. 
And  so,  when  the  chick  escapes  from  the  egg,  and  when  any  living  form 
is,  as  the  phrase  goes,  brought  into  the  world.  In  each  case,  however, 
birth  is  not  the  beginning  of  life,  but  only  the  continuation  of  it  under 
different  conditions.  To  understand  the  beginning  of  life  in  any  indi- 
vidual, whether  plant  or  animal,  existence  must  be  traced  somewhat 
further  back,  and  in  this  way  an  idea  gained  concerning  the  nature  of  the 
germ,  the  development  of  which  is  to  issue  in  birth. 

The  germ  may  be  defined  as  that  portion  of  the  parent  which  is  set 
apart  with  power  to  grow  up  into  the  likeness  of  the  being  from  which  it 
has  been  derived. 

The  manner  in  which  the  germ  is  separated  from  the  parent  does  not 
here  concern  us.  It  belongs  to  the  special  subject  of  generation.  Neither 
need  we  consider  apart  from  others  those  modes  of  propagation,  as  fission 
and  gemmation,  which  differ  more  apparently  than  really  from  the  or- 
dinary process  typified  in  the  formation  of  the  seed  or  ovum.  In  every 
case  alike,  a  new  individual  plant  or  animal  is  a  portion  of  its  parent:  it 
may  be  a  mere  outgrowth  or  bud,  which,  if  separated,  can  maintain  an 
independent  existence;  it  may  be  not  an  outgrowth  but  simply  a  portion 
of  the  parent's  structure,  which  has  been  naturally  or  artificially  cut  off, 
as  in  the  spontaneous  or  artificial  cleaving  of  a  polype;  it  may  be  the 
embryo  of  a  seed  or  ovum,  as  in  those  cases  in  which  the  process  of  mul- 
tiplication of  different  organs  has  reached  the  point  of  separation  of  the 
individual  more  or  less  completely  into  two  sexes,  the  mutual  conjugation 
of  a  portion  of  each  of  which,  the  sperm-cell  and  the  germ-cell,  is  necessary 
for  the  production  of  a  new  being.  We  are  so  accustomed  to  regard  the 
conjugation  of  the  two  sexes  as  necessary  for  what  is  called  generation, 
that  we  are  apt  to  forget  that  it  is  only  gradually  in  the  upward  progress 
of  development  of  the  vegetable  and  animal  kingdoms,  that  those  portions 
of  organized  matter  which  are  to  produce  new  beings  are  allotted  to  two 
separate  individuals.  In  the  least  developed  forms  of  life,  almost  any 
part  of  the  body  is  capable  of  assuming  the  characters  of  a  separate  indi- 
vidual; and  propagation,  therefore,  occurs  by  fission  or  gemmation  in 
some  form  or  other.  Then,  in  beings  a  little  higher  in  rank,  only  a 
special  part  of  the  body  can  become  a  separate  being,  and  only  by  conju- 
gation with  another  special  part.  Still,  there  is  but  one  parent;  and  this 
hermaphrodite-form  of  generation  is  the  rule  in  the  vegetable  and  least 
developed  portion  of  the  animal  kingdom.    At  last,  in  all  animals  but 


308 


HAND-BOOK  OF  PHYSIOLOGY. 


the  lowest,  and  in  some  plants,  the  portions  of  organized  structure  special- 
ized for  development  after  their  mutual  union  into  a  new  individual,  are 
found  on  two  distinct  beings,  which  we  call  respectively  male  and  female. 

The  old  idea  concerning  the  power  of  growth  resident  in  the  germ  of 
the  new  being,  thus  formed  in  various  ways,  was  expressed  by  saying  that 
a  store  of  dormant  vitality  was  laid  up  in  it,  and  that  so  long  as  no  de- 
composition ensued,  this  was  capable  of  manifesting  itself  and  becoming 
active  under  the  influence  of  certain  external  conditions.  Thus,  the 
dormant  force  supposed  to  be  present  in  the  seed  or  the  egg  was  assumed 
to  be  the  primary  agent  in  effecting  development  and  growth,  and  to  con- 
tinue in  action  daring  the  whole  term  of  life  of  the  living  being,  animal 
or  vegetable,  in  which  it  was  said  to  reside.  The  influence  of  external 
forces — heat,  light,  and  others — was  noticed  and  appreciated;  but  these 
were  thought  to  have  no  other  connection  with  vital  force  than  that  in 
some  way  or  other  they  called  it  into  action,  and  that  to  some  extent  it 
was  dependent  on  them  for  its  continuance.  They  were  not  supposed  to 
be  correlated  with  it  in  any  other  sense  than  this. 

Now,  however,  we  are  obliged  to  modify  considerably  our  notions  and 
with  them  our  terms  of  expression,  when  describing  the  origin  and  birth 
of  a  new  being. 

To  take,  as  before,  the  simplest  case — a  seed  or  egg.  We  must  sup- 
pose that  the  heat,  which  in  conjunction  with  moisture  is  necessary  for 
the  development  of  those  changes  which  issue  in  the  growth  of  a  new 
plant  or  animal,  is  not  simply  an  agent  which  so  stimulates  the  dormant 
vitality  in  the  seed  or  egg  as  to  make  it  cause  growth,  but  it  is  a  force, 
which  is  itself  transformed  into  chemical  and  vital  power.  The  embryo 
in  the  seed  or  egg  is  a  part  which  can  transform  heat  into  vital  force,  this 
term  being  a  convenient  one  wherewith  to  express  the  power  which  par- 
ticular structures  possess  of  growing,  developing,  and  performing  other 
actions  which  we  call  vital.  ^  Of  course  the  embryo  can  grow  only  by 
taking  up  fresh  matej*ial  and  incorporating  it  with  its  own  structure, 
and  therefore,  it  is  surrounded  in  the  seed  or  ovum  with  matter  sufficient 
for  nutrition  until  it  can  obtain  fresh  supplies  from  without.  The  ab- 
sorption of  this  nutrient  matter  involves  an  expenditure  of  force  of  some 
kind  or  other,  inasmuch  as  it  implies  the  raising  of  simple  to  more  com- 
plicated forms.  Hence  the  necessity  for  heat  or  some  other  power  before 
the  embryo  can  exhibit  any  sign  of  life.  It  would  be  quite  as  impossible 
for  the  germ  to  begin  life  without  external  force  as  witliout  a  supply  of 
nutrient  matter.  Without  the  force  wherewith  to  take  it,  the  matter 
would  be  useless.    The  heat,  therefore,  which  in  conjunction  with  mois- 


'  The  term  "  vitul  force  "  is  litn*e  employed  for  the  sake  of  brevit}^  Whether  it  is 
strictly  admissible  will  be  discussed  hereafter. 

The  general  term  force  is  used  as  syuonymous  With  what  is  now.  often  termed 
energy. 


THE  RELATION  OF  LIEE  TO  OTHER  FORCES. 


309 


ture  is  necessary  for  the  beginning  of  life,  is  partly  expended  as  chemical 
power,  which  causes  certain  modifications  in  the  nutrient  material  sur- 
rounding the  embryo,  e.g.,  the  transformation  of  starch  into  sugar  in  the 
act  of  germination;  partly,  it  is  transformed  by  the  germ  itself  into 
yital  force,  whereby  the  germ  is  enabled  to  take  up  the  nutrient  material 
presented  to  it,  and  arrange  it  in  forms  characteristic  of  life.  Thus  the 
force  is  expended,  and  thus  life  begins — when  a  particle  of  organized 
matter,  which  has  itself  been  produced  by  the  agency  of  life,  begins  to 
transform  external  force  into  vital  force,  or,  in  other  words,  into  a 
power  by  which  it  is  enabled  to  grow  and  develop.  This  is  the  true 
beginning  of  life.  The  time  of  .  birth  is  but  a  particular  period  in  the 
process  of  development,  at  which  the  germ,  having  arrived  at  a  fit  state 
for  a  more  independent  existence,  steps  forth  into  the  outer  world. 

The  term  ''dormant  vitality,"^  must  be  taken  to  mean  simply  the  exist- 
ence of  organized  matter  with  the  caparAty  of  transforming  heat  or  other 
force  into  vital  or  growing  power,  when  this  force  is  applied  to  it  under 
proper  conditions. 

The  state  of  dormant  vitality  is  like  that  of  an  empty  voltaic  battery, 
or  a  steam-engine  in  which  the  fuel  is  not  yet  lighted.  In  the  former 
case  no  electric  current  passes,  because  no  chemical  action  is  going  on. 
There  is  no  transformation  into  electric  force,  because  there  is  no  chem- 
ical force  to  be  transformed.  Yet,  we  do  not  say,  in  this  instance,  that 
there  is  a  store  of  electricity  laid  up  in  a  dormant  state  in  the  battery; 
neither  do  we  say  that  a  store  of  motion  is  laid  up  in  the  steam-engine. 
And  there  is  as  little  reason  for  saying  there  is  a  store  of  vitality  in  a 
dormant  seed  or  ovum. 

Next  to  the  beginning  of  life,  we  have  to  consider  how  far  its  continu- 
ance by  growth  and  development  is  dependent  on  external  force,  and  to 
what  extent  correlated  with  it. 

Mere  growth  is  not  a  special  peculiarity  of  living  beings.  A  crystal,  if 
placed  in  a  proper  solution,  will  increase  in  size  and  preserve  its  own  charac- 
teristic outline;  and  even  if  it  be  injured,  the  flaw  can  be  in  part  or  wholly 
repaired.  The  manner  of  its  growth,  however,  is  very  different  from  that 
of  a  living  being,  and  the  process  as  it  occurs  in  the  latter  will  be  made 
more  evident  by  a  comparison  of  the  two  cases.  The  increase  of  a  crystal 
takes  place  simply  by  the  laying  of  material  on  the  surface  only,  and  is 
unaccompanied  by  any  interstitial  change.  This  is,  however,  but  an 
accidental  difference.  A  much  greater  one  is  to  be  found  in  the  fact 
that  with  the  growth  of  a  crystal  there  is  no  decay  at  the  same  time,  and 
proceeding  with  it  side  by  side.  Since  there  is  no  life  there  is  no  need 
of  death — the  one  being  a  condition  consequent  on  the  other.  During 
the  whole  life  of  a  living  being,  on  the  other  hand,  there  is  unceasing 
change.  At  different  periods  of  existence  the  relation  between  waste  and 
repair  is  of  course  different.    In  early  life  the  addition  is  greater  than 


310 


HAND-BOOK  OF  PHYSIOLOGY. 


the  loss,  and  so  there  is  growth;  the  reconstructed  part  is  better  than  it 
was  before,  and  so  there  is  development.  In  the  decline  of  life,  on  the 
contrary,  the  renewal  is  less  than  the  destruction,  and  instead  of  devel- 
opment there  is  degeneration.  But  at  no  time  is  there  perfect  rest  or 
stability. 

It  must  not  be  supposed,  therefore,  that  life  consists  in  the  capability 
of  resisting  decay.  Formerly,  when  but  little  or  nothing  was  known 
about  the  laws  which  regulate  the  existence  of  living  beings,  it  was  rea- 
sonable enough  to  entertain  such  an  idea;  and,  indeed,  life  was  thought 
to  be,  essentially,  a  mysterious  power  counteracting  that  tendency  to 
decay  which  is  so  evident  when  life  has  departed.  Now,  we  know  that 
so  far  from  life  preventing  decomposition,  it  is  absolutely  dependent  upon 
it  for  all  its  manifestations. 

The  reason  of  this  is  very  evident.  Apart  from  the  doctrine  of  corre- 
lation of  force,  it  is  of  course  plain  that  tissues  which  do  work  must  sooner 
or  later  wear  out  if  not  constantly  supplied  with  nourishment;  and  the 
need  of  a  continual  supply  of  food,  on  the  one  hand,  and,  on  the  other, 
the  constant  excretion  of  matter  which,  having  evidently  discharged 
what  was  required  of  it,  was  fit  only  to  be  cast  out,  taught  this  fact  very 
plainly.  But  although,  to  a  certain  extent,  the  dependence  of  vital 
power  on  supplies  of  matter  from  without  was  recognized  and  appreciated, 
the  true  relation  between  the  demand  and  supply  was  not  until  recently 
thoroughly  grasped.  The  doctrine  of  the  correlation  of  vital  with  other 
forces  was  not  understood. 

To  make  this  more  plain,  it  will  be  well  to  take  an  instance  of  trans- 
formation of  force  more  commonly  known  and  appreciated.  In  the 
steam-engine  a  certain  amount  of  force  is  exhibited  as  motion,  and  the 
immediate  agent  in  the  production  of  this  is  steam,  which  again  is  the 
result  of  a  certain  expenditure  of  heat.  Thus,  heat  is  in  this  instance 
said  to  be  transformed  "into  motion,  or,  in  other  language,  one — molecular 
— mode  of  motion,  heat,  is  made  to  express  itself  by  another — mechanical 
— mode,  ordinary  movement.  But  the  heat  which  produced  the  vapor  is 
itself  the  product  of  the  combustion  of  fuel,  or,  in  other  words,  it  is  the 
correlated  expression  of  another  force — chemical,  namely,  that  affinity  of 
carbon  and  hydrogen  for  oxygen  which  is  satisfied  in  the  act  of  combus- 
tion. Again,  the  production  of  light  and  heat  by  the  burning  of  coal  and 
wood  is  only  the  giving  out  again  of  that  heat  and  light  of  the  sun  which 
were  used  in  their  production.  For,  as  it  need  scarcely  be  said,  it  is  only 
by  means  of  these  solar  forces  that  the  leaves  of  plants  can  decomi)ose 
carbonic  acid,  etc.,  and  thereby  provide  material  for  the  construction  of 
woody  tissue.  Thus,  coal  and  wood  being  i)i-oducts  of  the  expenditure 
of  force,  must  be  taken  to  represent  a  certain  amount  of  power;  and, 
according  to  the  law  of  tlie  correlation  of  forces,  must  be  capable  of  yield- 
ing, in  some  shape  or  other,  just  so  mucli  as  was  exercised  in  their  forma- 


THE  RELATION  OF  LIFE  TO  OTHER  FORCES. 


311 


tion.  The  amount  of  force  requisite  for  rending  asunder  the  elements  of 
carbonic  acid  is  exactly  that  amount  which  will  again  be  manifested 
when  they  clash  together  again. 

The  sun,  then,  really,  is  the  prime  agent  in  the  movement  of  the 
steam-engine,  as  it  is  indeed  in  the  production  of  nearly  all  the  power 
manifested  on  this  globe.  In  this  particular  instance,  speaking  roughly, 
its  light  and  heat  are  manifested  successively  as  vital  and  chemical  force 
in  the  growth  of  plants,  as  heat  and  light  again  in  the  burning  fuel,  and 
lastly  by  the  piston  and  wheels  of  the  engine  as  motive  power.  We  may 
use  the  term  transformation  of  force  if  we  will,  or  say  that  throughout 
the  cycle  of  changes  there  is  but  one  force  variously  manifesting  itself. 
It  matters  not,  so  that  we  keep  clearly  in  view  the  notion  that  all  force,  so 
far  at  least  as  our  present  knowledge  extends,  is  but  a  representative,  it 
may  be  in  the  same  form  or  another,  of  some  previous  force,  and  incapa- 
ble, like  matter,  of  being  created  afresh,  except  by  the  Creator.  Much 
of  our  knowledge  on  this  subject  is  of  course  confined  to  ideas,  and  gov- 
erned by  the  words  with  which  we  are  compelled  to  express  them,  rather 
than  to  actual  things  or  facts;  and  probably  the  term  force  will  soon  lose 
the  signification  which  we  now  attach  to  it.  What  is  now  known,  how- 
ever, about  the  relation  of  one  force  to  another,  is  not  sufificient  for  the 
complete  destruction  of  old  ideas;  and,  therefore,  in  applying  the  ex- 
amples of  transformation  of  physical  force  to  the  explanation  of  vital 
phenomena,  we  are  compelled  still  to  use  a  vocabulary  which  was  framed 
for  expressing  many  notions  now  obsolete.  • 

The  dependence  of  the  lowest  kind  of  vital  existence  on  external  force, 
and  the  manner  in  which  this  is  used  as  a  means  whereby  life  is  mani- 
fested, have  been  incidentally  referred  to  more  than  once  when  describing 
the  origin  of  vegetable  tissues.  The  main  functions  of  the  vegetable 
kingdom  are  construction,  and  the  perpetuation  of  the  race;  and  the  use 
which  is  made  of  external  physical  force  is  more  simple  than  in  animals. 
The  transformation  indeed  which  is  effected,  while  much  less  mysterious 
than  in  the  latter  instance,  forms  an  interesting  link  between  animal  and 
crystalline  growth. 

The  decomposition  of  carbonic  acid  or  ammonia  by  the  leaves  of  plants 
may  be  compared  to  that  of  water  by  a  galvanic  current.  In  both  cases  a 
force  is  applied  through  a  special  material  medium,  and  the  result  is  a 
separation  of  the  elements  of  which  each  compound  is  formed.  On  the 
return  of  the  elements  to  their  original  state  of  union,  there  will  be  the 
return  also  in  some  form  or  other  of  the  force  which  was  used  to  separate 
them.  Vegetable  growth,  moreover,  with  which  we  are  now  specially 
concerned,  resembles  somewhat  the  increase  of  unorganized  matter.  The 
accidental  difference  of  its  being  in  one  case  superficial,  and  in  the  other 
interstitial,  is  but  little  marked  in  the  process  as  it  occurs  in  the  more 
permanent  parts  of  vegetable  tissues.    The  layers  of  lignine  are  in  their 


312 


HAND-BOOK  OF  PHYSIOLOGY. 


arrangement  nearly  as  simple  as  those  of  a  crystal,  and  almost  or  quite  as 
lifeless.  After  their  deposition,  moreover,  they  undergo  no  further 
change  than  that  caused  by  the  addition  of  fresh  matter,  and  hence  they 
are  not  instances  of  that  ceaseless  waste  and  repair  which  have  been 
referred  to  as  so  characteristic  of  the  higher  forms  of  living  tissue.  There 
is,  however,  no  contradiction  here  of  the  axiom,  that  where  there  is  life 
there  is  constant  change.  Those  parts  of  a  vegetable  organism  in  which 
active  life  is  going  on  are  subject,  like  the  tissues  of  animals,  to  con- 
stant destruction  and  renewal.  But,  in  the  more  permanent  parts, 
life  ceases  with  deposition  and  construction.  Addition  of  fresh  matter 
may  occur,  and  so  may  decay  also  of  that  which  is  already  laid  down,  but 
the  two  processes  are  not  related  to  each  other,  and  not,  as  in  living  parts, 
inter-dependent.    Hence  the  change  is  not  a  vital  one. 

The  acquirement  in  growth,  moreover,  of  a  definite  shape  in  the  case 
of  a  tree,  is  no  more  admirable  or  mysterious  than  the  production  of  a 
crystal.  That  chloride  of  sodium  should  naturally  assume  the  form  of 
a  cube  is  as  inexplicable  as  that  an  acorn  should  grow  into  an  oak,  or  an 
ovum  into  a  man.  When  we  learn  the  cause  in  the  one  case  we  shall 
probably  in  the  other  also. 

There  is  nothing,  therefore,  in  the  products  of  life's  more  simple 
forms  that  need  make  us  start  at  the  notion  of  their  being  the  products 
of  only  a  special  transformation  of  ordinary  physical  force,  and  we  cannot 
doubt  that  the  growth  and  development  of  animals  obey  the  same  general 
laws  that  govern  the  formation  of  plants.  The  connecting  links  between 
them  are  too  numerous  for  the  acceptance  of  any  other  supposition. 
Both  kingdoms  alike  are  expressions  of  vital  force,  which  is  itself  but  a 
term  for  a  special  transformation  of  ordinary  physical  force.  The  mode 
of  the  transformation  is,  indeed,  mysterious,  but  so  is  that  of  heat  into 
light,  or  of  either  into  mechanical  motion  or  chemical  affiiiity.  All 
forms  of  life  are  as  absolutely  dependent  on  external  physical  force  as  a 
fire  is  dependent  for  its  continuance  on  a  supply  of  fuel;  and  there  is 
as  much  reason  to  be  certain  that  vital  force  is  an  expression  or  represen- 
tation of  the  physical  forces,  especially  heat  and  light,  as  that  these  are 
the  correlates  of  some  force  or  other  which  has  acted  or  is  acting  on  the 
substances  which,  as  we  say,  produce  them. 

In  the  tissues  of  plants,  as  just  said,  there  is  but  little  change,  except 
such  as  is  produced  by  additions  of  fresh  matter.  That  which  is  once 
deposited  alters  but  little;  or,  if  the  part  be  transient  and  easily  perishable, 
the  alteration  is  only  or  chiefly  one  produced  by  the  ordinary  process  of 
decay.  Little  or  no  force  is  manifested;  or,  if  it  be,  it  is  only  the  heat 
of  the  slow  oxidation  wlieroby  tlie  structure  again  returns  to  inorganic 
shape.  There  is  no  special  transformation  of  force  to  which  the  term 
vital  can  be  ap})lied.  With  construction  tlie  chief  end  of  vogetablo  exist- 
ence has  been  attained,  and  the  tissue  formed  represents  a  store  of  force 


THE  EELATION  OF  LIFE  TO  OTHER  FORCES. 


313 


to  be  used,  but  not  by  the  being  which  laid  it  up.  The  labors  of  the 
yegetable  world  are  not  for  itself,  but  for  animals.  The  power  laid  up 
by  the  one  is  spent  by  the  other.  Hence  the  reason  that  the  constant 
change,  which  is  so  great  a  character  of  life,  is  comparatively  but  little 
marked  in  plants.  It  is  present,  but  only  in  living  portions  of  the 
organism,  and  in  these  it  is  but  limited.  In  a  tree  the  greater  part  of 
the  tissues  may  be  considered  dead;  the  only  change  they  suffer  is  that 
fresh  matter  is  piled  on  to  them.  They  are  not  the  seat  of  any  transfor- 
mation of  force,  and  therefore,  although  their  existence  is  the  result  of 
living  action,  they  do  not  themselves  live.  Force  is,  so  to  speak,  laid  up 
in  them,  but  they  do  not  themselves  spend  it.  Those  portions  of  a 
vegetable  organism  which  are  doing  active  vital  work — which  are  using 
the  sun^s  light  and  heat  as  a  means  whereby  to  prepare  building  material, 
are,  however,  the  seat  of  unceasing  change.  Their  existence  as  living 
tissue  depends  upon  this  fact — upon  their  capability  of  perishing  and 
being  renewed. 

And  this  leads  to  the  answer  to  the  question,  What  is  the  cause  of 
the  constant  change  which  occurs  in  the  living  parts  of  animals  and 
vegetables,  which  is  so  invariable  an  accompaniment  of  life,  that  we 
refuse  the  title  of  "living"  to  parts  not  attended  by  it?  It  is  because  all 
manifestations  of  life  are  exhibitions  of  power;  and  as  no  power  can  be 
originated  by  us,  as,  according  to  the  doctrine  of  correlation  of  force,  all 
power  is  but  the  representative  of  some  previous  force  in  the  same  or 
another  form,  so,  for  its  production,  there  must  be  expenditure  and 
change  somewhere  or  other.  For  the  vital  actions  of  plants  the  light  and 
heat  of  the  sun  are  nearly  or  quite  sufficient,  and  there  is  no  need  of 
expenditure  of  that  store  of  force  which  is  laid  up  in  themselves;  but 
with  animals  the  case  is  different.  They  cannot  directly  transform  the 
solar  forces  into  vital  power;  they  must  seek  it  elsewhere.  The  great 
use  of  the  vegetable  kingdom  is  therefore  to  store  up  power  in  such  a 
form  that  it  can  be  used  by  animals;  that  so,  when  in  the  bodies  of  the 
latter,  vegetable  organized  material  returns  to  an  inorganic  condition, 
it  may  give  out  force  in  such  a  manner  that  it  can  be  transformed  by 
animal  tissues,  and  manifested  variously  by  them  as  vital  power. 

Hence,  then,  we  must  consider  the  waste  and  repair  attendant  on  liv- 
ing growth  and  development  as  something  more  than  these  words,  taken 
by  themselves,  imply.  The  waste  is  the  return  to  a  lower  from  a  higher 
form  of  matter;  and,  in  the  fall,  force  is  manifested.  This  force,  when 
specially  transformed  by  organized  tissues,  we  call  vital.  In  the  repair, 
force  is  laid  up.  The  analogy  with  ordinary  transmutations  of  physical 
force  is  perfect.  By  the  expenditure  of  heat  in  a  particular  manner  a 
weight  can  be  raised.  By  its  fall  heat  is  returned.  The  molecular 
motion  is  but  the  expression  in  another  form  of  the  mechanical.  So 
with  life.    There  is  constant  renewal  and  decay,  because  it  is  only  so  that 


314 


HAND-BOOK  OF  PHYSIOLOGY. 


vital  activity  can  take  place.  The  renewal  must  be  something  more  than 
replacement,  however,  as  the  decay  must  be  more  than  simple  mechanical 
loss.  The  idea  of  life  must  include  both  storing  up  of  force,  and  its 
transformation  in  the  expenditure. 

Hence  we  must  be  careful  not  to  confound  the  mere  preservation  of 
individual  form  under  the  circumstances  of  concurrent  waste  and  repair, 
with  the  essential  nature  of  vitality. 

Life,  in  its  simplest  form,  has  been  happily  expressed  by  Savory  as  a 
state  of  dynamical  equilibrium,  since  one  of  its  most  characteristic  fea- 
tures is  continual  decay,  yet  with  maintenance  for  the  individual  by  equally 
constant  repair.  Since,  then,  in  the  preservation  of  the  equilibrium  there 
is  ceaseless  change,  it  is  not  static  equilibrium  but  dynamical. 

Care  must  be  taken,  however,  not  to  accept  the  term  in  too  strict  a 
sense,  and  not  to  confound  that  which  is  but  a  necessary  attendant  on 
life  with  life  itself.  For,  indeed,  strictly,  there  is  no  preservation  of 
equilibrium  during  life.  Each  vital  act  is  an  advance  toward  death. 
We  are  accustomed  to  make  use  of  the  terms  growth  and  development  in 
the  sense  of  progress  in  one  direction,  and  the  words  decline  and  decay 
with  an  opposite  signification,  as  if,  like  the  ebb  of  the  tide,  there  w^ere 
after  maturity  a  reversal  of  lifers  current.  But,  to  use  an  equally  old 
comparison,  life  is  really  a  journey  always  in  one  direction.  It  is  an 
ascent,  more  and  more  gradual  as  the  summit  is  approached,  so  gradual 
that  it  is  impossible  to  say  when  development  ends  and  decline  begins. 
But  the  descent  is  on  the  other  side.  There  is  no  perfect  equilibrium, 
no  halting,  no  turning  back. 

The  term,  therefore,  must  be  used  with  only  a  limited  signification. 
There  is  preservation  of  the  individual,  yet,  although  it  may  seem  a  para- 
dox, not  of  the  same  individual.  A  man  at  one  period  of  his  life  may 
retain  not  a  particle  of  the  matter  of  which  formerly  he  was  composed. 
The  preservation  of  a  living  being  during  growth  and  development  is  more 
comparable,  indeed,  to  that  of  a  nation,  than  of  an  individual  as  the  term 
is  popularly  understood.  The  elements  of  which  it  is  made  up  fulfil  a 
certain  work  the  traditions  of  which  were  handed  down  from  their  pre- 
decessors, and  then  pass  away,  leaving  the  same  legacy  to  those  that  fol- 
low them.  The  individuality  is  preserved,  but,  like  all  things  handed 
doAvn  by  tradition,  its  fashion  changes,  until  at  last,  perhaps,  scarce  any 
likeness  to  the  original  can  be  discovered.  Or,  as  it  sometimes  happens, 
the  alterations  by  time  are  so  small  that  we  wonder,  not  at  the  change, 
but  the  want  of  it.  Yet,  in  both  cases  alike,  tlie  individuality  is  pre- 
served, not  by  the  same  individual  elements  throughout,  but  by  a  succes- 
sion of  them. 

Again,  concurrent  waste  and  repair  do  not  im]ily  of  necessity  tlie  exist- 
ence of  life.  It  is  true  tliat  living  beiui^s  are  the  chief  instances  of  tho 
simultaneous  occurrence  of  these  things.    But  this  happens  only  because 


THE  RELATION  OF  LIFE  TO  OTHER  FORCES. 


315 


the  conditions  under  which  the  functions  oi  life  are  discharged  are  the 
principal  examples  of  the  necessity  for  this  unceasing  and  mingled  de- 
struction and  renewal.  They  are  the  chief,  but  not  the  only  instances 
of  this  curious  conjunction. 

A  theoretical  case  will  make  this  plain.  Suppose  an  instance  of  some 
permanent  structure,  say  a  marble  statue.  If  we  imagine  it  to  be  placed 
under  some  external  conditions  by  which  each  particle  of  its  substance 
should  waste  and  be  replaced,  yet  with  maintenance  of  its  original  size 
and  shape,  we  obtain  no  idea  of  life.  There  is  waste  and  renewal,  Avith 
preservation  of  the  individual  form,  but  no  vitality.  And  the  reason  is 
plain.  With  the  waste  of  a  substance  like  carbonate  of  calcium  whose 
attractions  are  satisfied,  there  would  be  no  evolution  of  force;  and  even 
if  there  were,  no  structure  is  present  with  the  power  to  transform  or 
manifest  anew  any  power  which  might  be  evolved.  With  the  repair, 
likewise,  there  would  be  no  storing  of  force.  The  part  used  to  make 
good  the  loss  is  not  different  from  that  which  disappeared.  There  is 
therefore  neither  storing  of  force,  nor  its  transformation,  nor  its  expendi- 
ture; and  therefore  there  is  no  life. 

But  real  examples  of  the  preservation  of  an  individual  substance  under 
the  circumstances  of  constant  loss  and  renewal,  may  be  found,  yet  with- 
out any  semblance  in  them  of  life. 

Chemistry,  perhaps,  affords  some  of  the  neatest  and  best  examples 
of  this.  One,  suggested  by  Shepard,  seems  particularly  apposite.  It  is 
the  case  of  trioxide  of  nitrogen  (N2O3)  in  the  preparation  of  sulphuric 
acid.  The  gas  from  which  this  acid  is  obtained  is  sulphur  dioxide,  and 
the  addition  of  an  equivalent  of  oxygen  and  the  combination  of  the  re- 
sulting sulphur  trioxide  (SO3)  with  water  (H5O)  is  all  that  is  required. 
Thus: 

SO,     +     0    +    H,0  =  H,SO, 
Sulph.  dioxide  :  Oxygen  :  Water  =  Sulphuric  Acid. 

Sulphur  dioxide,  however,  cannot  take  the  necessary  oxygen  directly 
from  the  atmosphere,  but  it  can  abstract  it  from  trioxide  of  nitrogen 
(N2O3),  when  the  two  gases  are  mingled.  The  trioxide,  accordingly,  by 
continually  giving  up  an  equivalent  of  oxygen  to  an  equivalent  of  sulphur 
dioxide,  causes  the  formation  of  sulphuric  acid,  at  the  same  time  that  it 
retains  its  composition  by  continually  absorbing  a  fresh  quantity  of  oxy- 
gen from  the  atmosphere. 

In  this  instance,  then,  there  is  constant  waste  and  repair,  yet  without 
life.  And  here  an  objection  cannot  be  raised,  as  it  might  be  to  the  pre- 
ceding example,  that  both  the  destruction  and  repair  come  from  without, 
and  are  not  dependent  on  any  inherent  qualities  of  the  substance  with 
which  they  have  to  do.  The  waste  and  renewal  in  the  last-named  ex- 
ample are  strictly  dependent  on  the  qualities  of  the  chemical  compound 


316 


HAND-BOOK  OF  PHYSIOLOGY. 


which  is  subject  to  them.  It  has  but  to  be  placed  in  appropriate  condi- 
tions, and  destruction  and  repair  will  continue  indefinite^.  Force,  too, 
is  manifested,  but  there  is  nothing  present  which  can  transform  it  into 
vital  shape,  and  so  there  is  no  life. 

Hence,  our  notion  of  the  constant  decay  which,  together  with  repair, 
takes  place  throughout  life,  must  be  not  confined  to  any  simply  mechanical 
act.  It  must  include  the  idea,  as  before  said,  of  laying  up  of  force,  and 
its  expenditure — its  transformation  too,  in  the  act  of  being  expended. 

The  growth,  then,  of  an  animal  or  vegetable,  implies  the  expenditure 
of  physical  force  by  organized  tissue,  as  a  means  whereby  fresh  matter  is 
added  to  and  incorporated  with  that  already  existing.  In  the  case  of 
the  plant  the  force  used,  transformed,  and  stored  up,  is  almost  entirely 
derived  from  external  sources;  the  material  used  is  inorganic.  The  result 
is  a  tissue  which  is  not  intended  for  expenditure  by  the  individual  which 
has  accumulated  it.  The  force  expended  in  growth  by  animals,  on  the 
other  hand,  cannot  be  obtained  directly  from  without.  For  them  a 
supply  of  force  is  necessary  in  the  shape  of  food  derived  directly  or  indi- 
rectly from  the  vegetable  kingdom.  Part  of  this  force-containing  food 
is  expended  as  fuel  for  the  production  of  power;  and  the  latter  is  used 
as  a  means  wherewith  to  elaborate  another  portion  of  the  food,  and  incor- 
porate it  as  animal  structure.  Unlike  vegetable  structure,  however, 
animal  tissues  are  the  seat  of  constant  change,  because  their  object  is  not 
the  storing  up  of  power,  but  its  expenditure;  so  there  must  be  constant 
waste;  and  if  this  happen,  then  for  the  continuance  of  life  there  must 
be  equally  constant  repair.  But,  as  before  said,  in  early  life  the  repair 
surpasses  the  loss,  and  so  there  is  growth.  The  part  repaired  is  better 
than  before  the  loss,  and  thus  there  is  development. 

The  definite  limit  which  has  been  imposed  on  the  duration  of  life  has 
been  already  incidentally  referred  to.  Like  birth,  growth,  and  develop- 
ment, it  belongs  essentially  to  living  beings  only.  Dead  structures  and 
those  which  have  never  lived  are  subject  to  change  and  destruction,  but 
decay  in  them  is  uncertain  in  its  beginning  and  continuance.  It  de- 
pends almost  entirely  on  external  conditions,  and  differs  altogether  from 
the  decline  of  life.  The  decline  and  death  of  living  beings  are  as  definite 
in  their  occurrence  as  growth  and  development.  Like  these  they  may  be 
hastened  or  stayed,  especially  in  the  lower  forms  of  life,  by  various  influ- 
ences from  without;  but  the  putting  off  of  decline  must  be  the  patting 
off  also  of  so  much  life;  and,  apart  from  disease,  the  reverse  is  true  also. 
A  living  being  starts  on  its  career  with  a  certain  amount  of  work  to  do — 
various  infinitely  in  different  individuals,  but  for  each  well-defined.  In 
the  lowest  members  of  both  the  animal  and  vegetable  creation  the  prog- 
ress of  life  in  any  given  time  seems  to  depend  almost  entirely  on  external 
circumstances;  and  at  first  siglit  it  seems  almost  as  if  these  lowly-formed 
organisms  were  but  the  sport  of  the  surrounding  elements.    But  it  is 


THE  RELATION  OF  LIFE  TO  OTHER  FORCES. 


317 


only  so  in  appearance,  not  reality.  Each  act  of  their  life  is  so  much 
expended  of  the  time  and  work  allotted  to  them;  and  if,  from  absence 
of  those  surrounding  conditions  under  which  alone  life  is  possible,  their 
vitality  is  stayed  for  a  time,  it  again  proceeds  on  the  renewal  of  the 
necessary  conditions,  from  that  point  which  it  had  already  attained.  The 
amount  of  life  to  be  manifested  by  any  given  individual  is  the  same, 
whether  it  takes  a  day  or  a  year  for  its  expenditure.  Life  may  be  of 
course  at  any  moment  interrupted  altogether  by  disease  and  death.  But 
supposing  it,  in  any  individual  organism,  to  run  its  natural  course,  it  will 
attain  but  the  same  goal,  whatever  be  its  rate  of  movement.  Decline 
and  death,  therefore,  are  but  the  natural  terminations  of  life;  they  form 
part  of  the  conditions  on  whioh  vital  action  begins;  they  are  the  eud 
toward  which  it  naturally  tends.  Death,  not  by  disease  or  injury,  is  not 
so  much  a  violent  interruption  of  the  course  of  life,  as  the  attainment  of 
a  distant  object  which  was  in  view  from  the  commencement. 

In  the  period  of  decline,  as  during  growth,  life  consists  in  continued 
manifestations  of  transformed  physical  force;  and  there  is  of  necessity 
the  same  series  of  changes  by  which  the  individual,  though  bit  by  bit 
perishing,  yet  by  constant  renewal  retains  its  entity.  The  difference,  as 
has  been  more  than  once  said,  is  in  the  comparative  extent  of  the  loss  and 
reproduction.  In  decline  there  is  not  perfect  replacement  of  that  which 
is  lost.  Eepair  becomes  less  and  less  perfect.  It  does  not  of  necessity 
happen  that  there  is  any  decrease  of  the  quantity  of  material  added  in 
the  place  of  that  which  disappears.  But  although  the  quantity  may  not 
be  lessened,  and  may  indeed  absolutely  increase,  it  is  not  perfect  as  ma- 
terial for  repair,  and  although  there  may  be  no  wasting,  there  is  degen- 
eration. 

No  definite  period  can  be  assigned  as  existing  between  the  end  of 
development  and  the  beginning  of  decline,  and  chiefly  because  the  two 
processes  go  on  side  by  side  in  different  parts  of  the  same  organism.  The 
transition  as  a  whole  is  therefore  too  gradual  for  appreciation.  But,  after 
some  time,  all  parts  alike  share  in  the  tendency  to  degeneration;  until 
at  length,  being  no  longer  able  to  subdue  external  force  to  vital  shape, 
they  die;  and  the  elements  of  which  they  are  composed  simply  employ 
what  remnant  of  power,  in  the  shape  of  chemical  affinity,  is  still  left  in 
them,  as  a  means  whereby  they  may  go  back  to  the  inorganic  world.  Of 
course  the  same  process  happens  constantly  during  life;  but  in  death  the 
place  of  the  departing  elements  is  not  taken  by  others. 

Here,  then,  a  sharp  boundary  line  is  drawn  where  one  kind  of  action 
stops  and  the  other  begins;  where  physical  force  ceases  to  be  manifested 
except  as  physical  force,  and  where  no  further  vital  transformation  takes 
place,  or  can  in  the  body  ever  do  so.  For  the  notion  of  death  must  in- 
clude the  idea  of  impossibility  of  revival,  as  a  distinction  from  that  state 
of  what  is  called    dormant  vitality,"  in  which,  although  there  is  no  life^, 


318 


HAND-BOOK  OF  PHYSIOLOGY. 


tliere  is  capability  of  living.  Hence  the  e:5iplanation  of  the  difference 
between  the  effect  of  appliance  of  external  force  in  the  two  cases.  Take, 
for  examples,  the  fertile  but  not  yet  living  egg,  and  the  barren  or  dead 
one.  Every  application  of  force  to  the  one  must  excite  movement  in  the 
direction  of  development;  the  force,  if  used  at  all,  is  transformed  by  the 
germ  into  vital  energy,  or  the  power  by  which  it  can  gather  up  and  elab- 
orate the  materials  for  nutrition  by  which  it  is  surrounded.  Hence  its 
freedom  throughout  the  brooding  time  from  putrefaction.  In  the  other 
instance,  the  appliance  of  force  excites  only  degeneration;  if  transformed 
at  all,  it  is  only  into  chemical  force,  whereby  the  progress  of  destruction 
is  hastened;  hence  it  soon  rots.  To  the  one,  heat  is  the  signal  for  devel- 
opment, to  the  other  for  decay.  By  one  it  is  taken  up  and  manifested 
anew,  and  in  a  higher  form;  to  the  other  it  gives  the  impetus  for  a  still 
quicker  fall. 

Life,  then,  does  not  stand  alone.  It  is  but  a  special  manifestation  of 
transformed  force.  "But  if  this  be  so,^Mt  maybe  said — ''if  the  resem- 
blance of  life  to  other  forces  be  great,  are  not  the  differences  still  greater 

At  the  first  glance,  the  distinctions  between  living  organized  tissue 
and  inorganic  matter  seem  so  great  that  the  difficulty  is  in  finding  a  like- 
ness. And  there  is  no  doubt  that  these  wide  differences  in  both  outward 
configuration  and  intimate  composition  have  been  mainly  the  causes  of 
the  delay  in  the  recognition  of  the  claims  of  life  to  a  place  among  other 
forces.  And  reasonably  enough.  For  the  notion  that  a  plant  or  an  ani- 
mal can  have  any  kind  of  relationship  in  the  discharge  of  its  functions  to 
a  galvanic  battery  or  a  steam  engine  is  sufficiently  startling  to  the  most 
credulous.    But  so  it  has  been  proved  to  be. 

Among  the  distinctions  between  living  and  unorganized  matter,  that 
which  includes  differences  in  structure  and  proximate  chemical  composi- 
tion has  been  always  reckoned  a  great  one.  The  very  terms  organic  and 
inorganic  were,  until  quite  recently,  almost  synonymous  with  those  which 
implied  the  influence  of  life  and  the  want  of  it.  The  science  of  chem- 
istry, however,  is  a  great  leveller  of  artificial  distinctions,  and  many  com- 
plex substances  which,  it  was  supposed,  could  not  be  formed  without  the 
agency  of  life,  can  be  now  made  directly  from  their  elements  or  from  very 
simple  combinations  of  these.  The  number  of  complex  substances  so 
formed  artificially  is  constantly  increasing;  and  there  seems  to  be  no  rea- 
son for  doubting  that  even  such  as  albumin,  gelatin,  and  the  like,  will  be 
ultimately  produced  without  the  intermediation  of  living  structure. 

The  formation  of  the  latter,  such  an  organized  structure  for  instance 
as  a  cell  or  a  muscular  fibre,  is  a  different  thing  altogetlier.  Tliere  is  at 
present  no  reason  for  believing  that  such  will  ever  be  formed  by  artificial 
means;  and,  therefore,  among  the  peculiarities  of  living  force-transform- 
ing agents,  must  be  reckoned  as  a  great  and  essential  one,  a  special  in- 
timate structure,  apart  from  mere  ultimate  or  proximate  chemical  coni' 


THE  RELATION  OF  LIFE  TO  OTHER  FORCES. 


319 


position,  to  which  there  is  no  close  likeness  in  any  artificial  apparatus, 
even  the  most  complicated.  This  is  the  real  distinction,  as  regards  com- 
position, between  a  living  tissue  and  an  inorganic  machine;  namely,  the 
difference  between  the  structural  arrangement  by  which  force  is  trans- 
formed and  manifested  anew.  The  fact  that  one  agent  for  transforming 
force  is  made  of  albumen  or  the  like,  and  another  of  zinc  or  iron,  is  a 
great  distinction,  but  not  so  essential  or  fundamental  a  one  as  the  differ- 
ence in  mechanical  structure  and  arrangement. 

In  proceeding  to  consider  the  difference  between  what  may  be  called 
the  transformation-products  of  living  tissue,  and  of  an  artificial  machine, 
it  will  be  well  to  take  one  of  the  simple  cases  first — the  production  of 
mechanical  motion;  and  especially  because  it  is  so  common  in  both. 

In  one  we  can  trace  the  transformation.  We  know,  as  a  fact,  that  heat 
produces  expansion  (steam),  and  by  constructing  an  apparatus  which  pro- 
vides for  the  application  of  the  expansive  power  in  opposite  directions 
alternately,  or  by  alternating  contraction  with  expansion,  we  are  able  to 
produce  motion  so  as  to  subserve  an  infinite  variety  of  purposes.  For 
the  continuance  of  the  motion  there  must  be  a  constant  supply  of  heat, 
and  therefore  of  fuel. 

In  the  production  of  mechanical  motion  by  the  alternate  contractions 
of  muscular  fibres  we  cannot  trace  the  transformation  of  force  at  all.  We 
know  that  the  constant  supply  of  force  is  as  necessary  in  this  instance  as 
in  the  other;  and  that  the  food  which  an  animal  absorbs  is  as  necessary  as 
the  fuel  in  the  former  case,  and  is  analogous  with  it  in  function.  In 
what  exact  relation,  however,  the  latent  force  in  the  food  stands  to  the 
movement  in  the  fibre,  we  are  at  present  quite  ignorant.  That  in  some 
way  or  other,  however,  the  transformation  occurs,  we  may  feel  quite  certain. 

There  is  another  distinction  between  the  two  exhibitions  of  force  which 
must  be  noticed.  It  has  been  universally  believed,  almost  up  to  the  pres- 
ent time,  that  in  the  production  of  living  force  the  result  is  obtained  by 
an  exactly  corresponding  waste  of  the  tissue  which  produces  it;  that,  for 
instance,  the  power  of  each  contraction  of  a  muscle  is  the  exact  equiv- 
alent of  the  force  produced  by  the  more  or  less  complete  descent  of  so 
much  muscular  substance  to  inorganic,  or  less  complex  organic  shape;  in 
other  words, — that  the  immediate  fuel  which  an  animal  requires  for  the 
production  of  force  is  derived  from  its  own  substance;  and  that  the  food 
taken  must  first  be  appropriated  by,  and  enter  into,  the  very  formation 
of  living  tissue  before  its  latent  force  can  be  transformed  and  manifested 
as  vital  power.  And  here,  it  might  be  said,  is  a  great  distinction  between 
a  living  structure  and  a  simply  mechanical  arrangement  such  as  that 
which  has  been  used  for  comparison;  the  fuel  which  is  analogous  to  the 
food  of  a  plant  or  animal  does  not,  as  in  the  case  of  the  latter,,  first  form 
part  of  the  machine  which  transforms  its  latent  energy  into  another 
variety  of  power. 


320 


HAND-BOOK  OF  PHYSIOLOGY. 


We  are  not,  at  present,  in  a  position  to  deny  that  this  is  a  real  and 
great  distinction  between  the  two  cases;  but  modern  investigations  in 
more  than  one  direction  lead  to  the  belief  that  we  must  hesitate  before 
allowing  such  a  difference  to  be  a  universal  or  essential  one.  The  experi- 
ments referred  to  seem  conclusive  in  regard  to  the  production  of  muscular 
power  in  greater  amount  than  can  be  accounted  for  by  the  products  of 
muscular  waste  excreted;  and  it  may  be  said  with  justice,  that  there  is  no 
intrinsic  improbability  in  the  supposed  occurrence  of  transformation  of 
force,  apart  from  equivalent  nutrition  and  subsequent  destruction  of  the 
transforming  agent.  Argument  from  analogy,  indeed,  would  be  in  favor 
of  the  more  recent  theory  as  the  likelier  of  the  two. 

Whatever  may  be  the  result  of  investigations  concerning  the  relation 
of  waste  of  living  tissue  to  the  production  of  power,  there  can  be  no 
doubt,  of  course,  that  the  changes  in  any  part  which  is  the  seat  of  vital 
action  must  be  considerable,  not  only  from  what  may  be  called  ^*wear  and 
tear,'"  but,  also,  on  account  of  the  great  instability  of  all  organized  struc- 
tures. Between  such  waste  as  this,  however,  and  that  of  an  inorganic 
machine  there  is  only  the  difference  in  degree,  arising  necessarily  from 
diversity  of  structure,  of  elemental  arrangement,  and  so  forth.  But  the 
repair  in  the  two  cases  is  different.  The  capability  of  reconstruction  in 
a  living  body  is  an  inherent  quality  like  that  which  causes  growth  in  a 
special  shape  or  to  a  certain  degree.  At  present  we  know  nothing  really 
of  its  nature,  and  we  are  therefore  compelled  to  express  the  fact  of  its 
existence  by  such  terms  as  ''inherent  power,"  "individual  endowment,^' 
and  the  like,  and  wait  for  more  facts  which  may  ultimately  explain  it. 
This  special  quality  is  not  indeed  one  of  living  things  alone.  The  repair 
of  a  crystal  in  definite  shape  is  equally  an  ''individual  endowment,"'  or 
* 'inherent  peculiarity,"  of  the  nature  of  which  we  are  equally  ignorant. 
In  the  case,  however,  of  an  inorganic  machine  there  is  nothing  of  the 
sort,  not  even  as  in  a  crystal.  Faults  of  structure  must  be  repaired  by 
some  means  entirely  from  without.  And  as  our  notion  of  a  living  being, 
say  a  horse,  would  be  entirely  altered  if  flaws  in  his  comj^wsition  were 
repaired  by  external  means  only;  so,  in  like  manner,  would  our  idea  of  the 
nature  of  a  steam-engine  be  completely  changed  had  it  the  power  of  ab- 
sorbing and  using  part  of  its  fuel  as  matter  wherewith  to  repair  any  ordi- 
nary injury  it  might  sustain. 

It  is  this  ignorance  of  the  nature  of  such  an  act  as  reconstruction 
which  causes  it  to  be  said,  with  apparent  reason,  that  so  long  as  tlie  term 
"vital  force"  is  used,  so  long  do  we  beg  the  question  at  issue — AVhat  is 
the  nature  of  life?  A  little  consideration,  however,  will  show  that  the  jus- 
tice of  this  criticism  depends  on  the  manner  in  whicli  the  word  ''vital"  is 
used.  If  by  it  we  intend  to  express  an  idea  of  something  wliicli  arises  in 
a  totally  different  manner  from  otlier  forces — something  wliich,  we  know 
not  how,  depends  on  a  special  innate  quality  of  living  beings,  and  owns  no 


THE  RELATION  OF  LIFE  TO  OTHER  FORCES. 


321 


dependence  on  ordinary  physical  force,  but  is  simply  stimulated  by  it, 
and  has  no  correlation  with  it — then,  indeed,  it  would  be  just  to  say  that 
the  whole  matter  is  merely  shelved  if  we  retain  the  term  ''vital  force.'' 

But  if  a  distinct  correlation  be  recognized  between  ordinary  physical 
force  and  that  which  in  various  shapes  is  manifested  by  living  beings;  if 
it  be  granted  that  every  act — say,  for  example,  of  a  brain  or  muscle — is 
the  exactly  correlated  expression  of  a  certain  quantity  of  force  latent  in 
the  food  with  which  an  animal  is  nourished;  and  that  the  force  produced 
either  in  the  shape  of  thought  or  movement  is  but  the  transformed  expres- 
sion of  external  force,  and  can  no  more  originate  in  a  living  organ  with- 
out supplies  of  force  from  without,  than  can  that  organ  itself  be  formed 
or  nourished  without  supplies  of  matter; — if  these  facts  be  recognized, 
then  the  term  used  in  speaking  of  the  powers  exercised  by  a  living  being 
is  not  of  very  much  consequence.  We  have  as  much  right  to  use  the 
term  "vitaF  as  the  words  galvanic  and  chemical.  All  alike  are  but  the 
expressions  of  our  ignorance  concerning  the  nature  of  that  power  of 
which  all  that  we  call  "forces''  are  various  manifestations.  The  differ- 
ence is  in  the  apparatus  by  which  the  force  is  transformed. 

It  is  with  this  meaning  that,  for  the  present,  the  term  "vital  force" 
may  still  be  retained  when  we  wish  shortly  to  name  that  combination  of 
energies  which  we  call  life.  For,  exult  as  we  may  at  the  discovery  of  the 
transformation  of  physical  force  into  vital  action,  we  must  acknowledge 
not  only  that,  with  the  exception  of  some  slight  details,  we  are  utterly 
ignorant  of  the  process  by  which  the  transformation  is  effected;  but,  as 
well,  that  the  result  is  in  many  ways  altogether  different  from  that  of  any 
other  force  with  which  we  are  acquainted. 

It  is  impossible  to  define  in  what  respects,  exactly,  vital  force  differs 
from  any  other.  For  while  some  of  its  manifestations  are  identical  with 
ordinary  physical  force,  others  have  no  parallel  whatsoever.  And  it  is 
this  mixed  nature  which  has  hitherto  baffled  all  attempts  to  define  life, 
and,  like  a  Will-o'-the-wisp,  has  led  us  floundering  on  through  one  defini- 
tion after  another  only  to  escape  our  grasp  and  show  our  impotence  to 
seize  it. 

.  In  examining,  therefore,  the  distinctions  between  the  products  of 
transformations  by  a  living  and  by  an  inorganic  machine,  we  have  first  to 
recognize  the  fact,  that  while  in  some  cases  the  difference  is  so  faint  as  to 
be  nearly  or  quite  imperceptible,  in  others  there  seems  not  a  trace  of 
resemblance  to  be  discovered. 

In  discussing  the  nature  of  life's  manifestations — birth,  growth,  devel- 
opment, and  decline — the  differences  which  exist  between  them  and  gtfier 
processes  more  or  less  resembling  them,  but  not  dependent  on  lifef  have 
been  already  briefly  considered  and  need  not  be  here  repeated.  It  may 
be  well,  however,  to  sum  up  very  shortly  the  particulars  in  which  life  as 
a  manifestation  of  force  differs  from  all  others. 
Vol.  II.— 21. 


322 


HAND-BOOK  OF  PHYSIOLOGY. 


The  mere  acquirement  of  a  certain  shape  by  growth  is  not  a  pecu- 
liarity of  life.  But  the  power  of  developing  into  so  composite  a  mass  even 
as  a  vegetable  cell  is  a  property  possessed  by  an  organized  being  only.  In 
the  increase  of  inorganic  matter  there  is  no  development.  The  minutest 
crystal  of  any  given  salt  has  exactly  the  same  shape  and  intimate  struc- 
ture as  the  largest.  With  the  growth  there  is  no  development.  There  is 
increase  of  size  with  retention  of  the  original  shape^  but  nothing  more. 
And  if  we  consider  the  matter  a  little  we  shall  see  a  reason  for  this.  In 
all  force -transformers,  whether  living  or  inorganic,  with  but  few  ex- 
ceptions — and  these  are,  probably,  apparent  only — something  more  is 
required  than  homogeneity  of  structure.  There  seems  to  be  a  need  for 
some  mutual  dependence  of  one  part  on  another,  some  distinction  of 
qualities,  which  cannot  happen  when  all  portions  are  exactly  alike.  And 
here  lies  the  resemblance  between  a  living  being  and  an  artificial  machine. 
Both  are  developments,  and  depend  for  their  power  of  transforming  force 
on  that  mutual  relation  of  the  several  parts  of  their  structure  which  we 
call  organization.  But  here,  also,  lies  a  great  difference.  The  develop- 
ment of  a  living  being  is  due  to  an  inherent  tendency  to  assume  a  certain 
form;  about  which  tendency  we  know  absolutely  nothing.  We  recognize 
the  fact,  and  that  is  all.  The  development  of  an  inorganic  machine — 
say  an  electrical  apparatus — is  not  due  to  any  inherent  or  individual 
property.  It  is  the  result  of  a  power  entirely  from  without;  and  we 
know  exactly  how  to  construct  it. 

Here,  then,  again,  we  recognize  the  compound  nature  of  a  living 
being.  In  structure  it  is  altogether  different  from  a  crystal — in  inherent 
capacity  of  growth  into  definite  shape  it  resembles  it.  Again,  in  the  fact 
of  its  organization  it  resembles  a  machine  made  by  man:  in  capacity  of 
growth  it  entirely  differs  from  it.  In  regard,  therefore,  to  structure, 
growth,  and  development,  it  has  combined  in  itself  qualities  which  in  all 
other  things  are  more  or  less  completely  separated. 

That  liiodiffc^ffeipn  of  ordinary  growth  and  development  called  gener- 
ation, which  consisStin  the  natural  production  and  separation  of  a  portion 
of  organized  structiwe,  with  power  itself  to  transform  force  so  as  there- 
with to  build  up  an  drganism  like  the  being  from  which  it  was  thrown 
off,  is  another  distiuxitive  peculiarity  of  a  living  being.  We  know  of 
nothing  like  it  in  the  inorganic  world.  And  the  distinction  is  the  greater 
betrause  iL'is  the  fulfilment  of  a  purpose,  toward  which  life  is  evidently, 
from  its^very  beginning,  constantly  tending.  It  is  as  natural  a  destiny 
t^separate  parts  which  shall  form  independent  beings  as  it  is  to  develop 
a  iWh.  Hence  it  is  another  instance  of  that  carrying  out  of  certain  pro- 
jects^'om  the  very  beginning  in  view,  which  is  so  characteristic  of  things 
living  and  of  no  other. 

It  is  especially  in  the  discharge  of  what  are  called  the  animal  func- 
tions that  we  see  vital  force  most  strangely  manifested.    It  is  true  that 


THE  RELATION-  OF  LIFE  TO  OTHER  FORCES. 


323 


one  of  the  actions  included  in  this  term — namely,  mechanical  movement 
— although  one  of  the  most  striking,  is  by  no  means  a  distinctive  one. 
For  it  must  be  remembered  that  one  of  the  commonest  trarsformations  of 
physical  force  with  which  we  are  acquainted  is  that  of  heat  into  mechani- 
cal motion,  and  that  this  may  be  effected  by  an  apparatus  having  itself 
nothing  whatever  to  do  with  life.  The  peculiarity  of  the  manifestation 
in  an  animal  or  vegetable  is  that  of  the  organ  by  which  it  is  effected,  and 
the  manner  in  which  the  transformation  takes  place,  not  in  the  ultimate 
result.  The  mere  fact  of  an  animaFs  possessing  capability  of  movement 
is  not  more  wonderful  than  the  possession  of  a  similar  property  by  a  steam 
engine.  In  both  cases  alike,  the  motion  is  the  correlative  expression  of 
force  latent  in  the  food  and  fuel  respectively;  but  in  one  case  we  can 
trace  the  transformation  in  the  arrangement  of  parts,  in  the  other  we 
cannot. 

The  consideration  of  the  products  of  the  transformation  of  force 
effected  by  the  nervous  system  would  lead  far  beyond  the  limits  of  the 
present  chapter.  But  although  the  relation  of  mind  to  matter  is  so  little 
known  that  it  is  impossible  to  speak  with  any  freedom  concerning  such 
correlative  expressions  of  physical  force  as  thought  and  nerve-products, 
still  it  cannot  be  doubted  that  they  are  as  much  the  results  of  transfor- 
mation of  force  as  the  mechanical  motion  caused  by  the  contraction  of  a 
muscle.  But  here  the  mystery  reaches  its  climax.  We  neither  know 
how  the  change  is  effected,  nor  the  nature  of  the  product,  nor  its  analo- 
gies with  other  forces.  It  is  therefore  better,  for  the  present,  to  confess 
our  ignorance,  than,  with  the  knowledge  which  we  have  lately  gained,  to 
build  up  rash  theories,  serving  only  to  cause  that  confusion  which  is 
worse  than  error. 

It  may  be  said,  with  perfect  justice,  that  even  if  the  foregoing  conclu- 
sions be  accepted,  namely,  that  all  manifestations  of  force  by  living  beings 
are  correlative  expressions  of  ordinary  physical  force,  s^jgbb^  argument 
is  based  on  the  assumption  of  the  existence  of  the j^paratus  ^^^^ch  we 
call  living  organized  matter,  with  power  not  onlyzo  use  ext^^lVorce 
for  its  own  use  in  growth,  development,  and  other  ^al  ma"!^estati(&s,  but 
for  that  modification  of  these  powers  which  consilis^n  the  &eparai;ion  of 
a  part  that  shall  grow  up  into  the  likeness  of  its  parent,  and)  f^iis'^^ 
tinue  the  race.    We  are  therefore,  it  may  added,  aliJ\far  a^  er^ from  ar 
explanation  of  the  origin  of  life.    This  is  of  course  miite  tru^(p^h^l 
ject  of  the  present  chapter,  however,  is  only  to  deal  wik^the  rl^fations 
life,  as  it  now  exists,  to  other  forces.    The  manner  ol^NCTeation  oi^ 
various  kinds  of  organized  matter,  and  the  source  of  ftidsig^^SS^^^^s, 
belonging  to  it,  which  from  our  ignorance  we  call  inherent,  are  different 
questions  altogeth 

To  say  that  of  necessity  the  power  to  form  living  organized  matter 
will  never  be  vouchsafed  to  us,  that  it  is  only  a  mere  materialist  who 


324 


HAND-BOOK  OF  PHYSIOLOGY. 


would  believe  in  sucli  a  possibility,  seems  almost  as  absurd  as  the  state- 
ment that  such  inquiries  lead  of  necessity  to  the  denial  of  any  higher 
power  than  that  which  in  various  forms  is  manifested  as  ''force/'  on  this 
small  portion  of  the  universe.  It  is  almost  as  absurd,  but  not  quite. 
For,  surely,  he  who  recognizes  the  doctrine  of  the  mutual  convertibility 
of  all  forces,  vital  and  physical,  who  believes  in  their  unity  and  imperish- 
ableness,  should  be  the  last  to  doubt  the  existence  of  an  all-powerful  Being, 
of  whose  will  they  are  but  the  various  correlative  expressions;  from  whom 
they  all  come;  to  whom  they  return. 


APPENDIX 


A. 


The  Chemical  Basis  oe  the  Humait  Body. 


Of  the  sixty-four  known  chemical  elements  no  less  than  seventeen  have 
been  found,  in  larger  or  smaller  quantities,  to  form  the  chemical  basis  of 
the  animal  body. 

The  substances  occurring  in  largest  quantities  are  the  non-metallic  ele- 
ments. Oxygen,  Carbon,  Hydrogen,  and  Nitrogen — oxygen  and  carbon 
making  up  altogether  about  85  per  cent,  of  the  whole.  The  most  abun- 
dant of  the  metallic  elements  are  Calcium,  Sodium,  and  Potassium. 

The  following  table  represents  the  relative  proportion  of  the  various 
elements. — (Marshall.) 


Oxygen  .......  72-0 

Carbon  13-5 

Hydrogen   9  *! 

Nitrogen   2  '5 

Calcium   1  -3 

Phosphorus   1*15 

Sulphur  -1476 

Sodium      ......  '1 

Chlorine  -085 


Fluorine   '08 

Potassium   '026 

Iron   -01 

Magnesium     .    •    .    .    .  -0012 

Silicon   -0002 

(Traces  of  copper,  lead,  and 
aluminium)  .... 


100" 


Compounds. — The  elementary  substances  above-mentioned  seldom 
occur  free  or  uncombined  in  the  animal  body;  but  are  nearly  always 
united  among  themselves  in  various  numbers,  and  in  variable  proportions 
to  form  '^compounds  "  Several  elements  have,  however,  been  detected 
in  small  amount  free;  traces  of  uncombined  Oxygen  and  Nitrogen  have 
been  found  in  the  blood,  and  of  Hydrogen  as  well  as  of  Oxygen  and 
Nitrogen  in  the  intestinal  canal. 

Organic  and  Inorganic  Compounds. — It  was  formerly  thought 
that  the  more  complex  compounds  built  up  by  the  animal  or  vegetable 
organism  were  peculiar,  and  could  not  be  made  artificially  by  chemists 
from  their  elements,  and  under  this  idea  they  were  formed  into  a  distinct 
class,  termed  organic.  This  idea  has  been  given  up,  but  the  name  is  still 
in  use,  with  a  different  signification.    The  term  organic  is  now  applied 


326 


HAND-BOOK  OF  PHYSIOLOGY. 


simply  to  the  compounds  of  tlie  element  Carbon,  irrespective  of  their 
complexity;  chemists  having  found  that  these  compounds  are  so  numer- 
ous and  important,  and  that  they  include  all  those  to  Avhich  the  term 
organic  was  in  former  times  exclusively  given. 

Characteristics  of  Organic  Compounds. — The  animal  organic 
compounds  are  characterized  as  a  rule  by  their  complexity,  for  in  the 
first  place  many  elements  enter  into  their  composition,  thereby  distin- 
guishing them  from  bodies  such  as  water  (H^O),  hydrochloric  acid  (HCl), 
and  ammonia  (NH3),  which  may  be  taken  as  types  of  inorganic  com- 
pounds. And  again,  because  many  atoms  of  the  same  element  occur 
in  each  molecule.  This  latter  fact  no  doubt  explains  also  the  reason  of 
the  instability  of  organic  compounds. 

Another  great  cause  of  the  instability  arises  from  the  fact  that  many 
such  compounds  contain  the  element  Nitrogen,  which  may  be  called 
negative  or  undecided  in  its  affinities,  and  may  be  easily  separated  from 
combination  with  other  elements. 

Animal  tissues,  containing  as  they  do  these  organic  nitrogenous  com- 
pounds, are  extremely  prone  to  undergo  chemical  decomposition,  and 
this  is  especially  the  case  since  they  also  contain  a  large  quantity  of  water, 
a  condition  most  favorable  for  the  breaking  up  of  such  substances.  It 
is  from  this  fact  that  in  the  consideration  of  the  chemical  basis  of  the 
body  we  meet  with  an  extremely  large  number  of  decomposition  products. 

In  treating  of  the  various  substances  found  in  the  animal  organism 
it  is  convenient  to  adopt  the  division  into — 


(a)  Nitrogenous  todies  take  the  chief  part  in  forming  the  sblid  tissues 
of  the  body,  and  are  found  to  a  considerable  extent  in  the  circulating 
fluids  (blood,  lymph,  chyle),  the  secretions  and  excretions.  They  contain 
often  in  addition  to  Carbon,  Hydrogen,  Nitrogen,  and  Oxygen,  the  ele- 
ments Sulphur  and  Phosphorus;  but  although  the  composition  of  most 
of  them  is  approximately  known,  no  general  rational  formula  can  at 
present  be  given. 

Several  classes  of  animal  nitrogenous  bodies  may  be  distinguished, 
and  it  is  convenient  to  consider  them  under  the  following  heads: — 

(1.)  Albuminoids  or  proteids. 

(2.)  Gelatinous  substances. 

I'^.S  Decomposition  nitrogenous  bodies. 

(4.)  Certain  su])i)()scd  nitrogenous  bodies,  the  exact  composition  of 
which  has  not  been  made  out. 


2.  Inorganic, 


1.  Orgakic. 


APPENDIX. 


327 


(1.)  Albummoids  or  Proteids  are  the  most  important  of  the  nitroge- 
nous animal  compounds,  one  or  more  of  them  entering  as  essential  parts 
into  the  formation  of  all  living  tissue.  In  the  lymph,  chyle,  and  blood, 
they  also  exist  abundantly.  Their  atomic  formula  is  uncertain.  Their 
composition  may  be  taken  as — 


Carbon      .  .  from  51*5  to  54*5 

Hydrogen  .  .  "      6-9  7*3 

Nitrogen    .  .  15-2  17' 

Oxygen      .  .      "     20-9  23-5 

Sulphur     .  •     "        -3"   2-  (Hoppe-Seyler.) 


Physical  Properties. — Proteids  are  all  amorphous  and  non-crystalliza- 
ble,  so  that  they  possess  as  a  rule  no  power  (or  scarcely  any)  of  passing 
through  animal  membranes.  They  are  soluble,  but  undergo  alteration  in 
composition  in  strong  acids  and  alkalies;  some  are  soluble  in  water,  others 
in  neutral  saline  solutions,  some  in  dilute  acids  and  alkalies,  few  in 
alcohol  or  ether.  Their  solutions  have  a  left-handed  action  on  polarized 
light. 

Chemical  Properties. — Certain  general  reactions  are  given  for  proteids. 
They  are  a  little  varied  in  each  particular  case: — 

i.  — A  solution  boiled  with  strong  nitric  acid,  becomes  yellow, 

and  this  yellowness  gets  darker  on  addition  of  ammonia 
(xantho-proteic  reaction). 

ii.  — With  potassium  f  errocyanide  and  acetic  acid,  they  give  a  white 

precipitate. 

m. — With  a  trace  of  copper  sulphate  and  an  excess  of  potassium 
or  sodium  hydrate  they  give  a  purple  coloration. 

iv. — With  Millon^s  reagent  (mixed  nitrate  and  nitrite  of  mercury?), 
they  give  a  white  or  pinkish  precipitate,  becoming  more 
pink  on  boiling. 

V. — When  boiled  with  sodium  sulphate  and  acetic  acid,  a  white 
precipitate  is  thrown  down. 

It  is  usual  to  place  Proteids  into  the  following  sub-classes,  thus: — 


(d.)  Fibrinogen, 
(e. )  Vitellin,  etc. 

IV. — FiBEiJ^.      V. — Peptones.       VI. — Coagulated  Proteids. 
VII.  — Lard  acein. 


I.  II. 

Native  Albumins.  Derived  Albumins. 

Egg-Albumin.  Acid-Albumin. 

Serum- Albumin.  Alkali- Albumin. 


III. 

Globulin. 
(a.)  Globulin. 


Casein. 


Classes  of  Proteids. 


I.  The  Native  Albumins  are  soluble  in  water  and  in  saline  solutions 
coagulable  by  heating,  not  precipitated  by  acetic  or  normal  phosphoric 
acid.    Serum-albumin  (p.  85,  Vol.  I. )  is  distinguished  from  egg-albumin 


328      .  HAND-BOOK  OF  PHYSIOLOGY. 

in  being  soluble  in  ether  and  in  not  so  easily  giving  a  precipitate  with 
strong  hydrochloric  acid;  the  precipitate  being  easily  redissolved  in  excess 
of  the  acid.  Serum-albumin  is  found  in  the  blood,  lymph  and  serous  and 
synovial  fluids,  and  the  tissues  generally;  it  appears  in  the  urine  in  the 
condition  known  as  albuminuria.  Two  varieties,  metalhumin  and  paraJ- 
humin  have  been  described  as  existing  in  dropsical  fluids  and  ovarian 
cysts  respectively. 

II.  Derived  Albumins  are  made  by  adding  dilute  acids  or  alkalies 
to  solutions  of  native-albumin.  They  are  insoluble  in  water  or  in  neutral 
saline  solutions,  and  are  not  coagulated  by  heat.  Both  the  native -albu- 
mins and  the  next  two  classes  (iii.  and  iv.)  of  proteids  generally  undergo 
change  into  either  acid  or  alkali  albumin  on  the  addition  of  acids  or  al- 
kalies, and  foods  containing  either  albumins  or  globulins  change  first  of 
all  into  one  or  other  of  these  compounds,  according  as  they  are  acted 
upon  by  the  gastric  or  pancreatic  juices  respectively.  Acid-albumin  is 
called  also  syntonin,  and  is  either  identical  with  or  akin  to  it.  Casein  is 
very  probably  natural  alkali- albumin,  and  exists  in  milk,  being  kept  in 
solution  by  the  alkaline  phosphates;  it  exists  also  in  the  serum  and  serous 
fluids  in  small  quantity,  and  in  muscle.  It  is  not  coagulable  by  heat,  and 
so  corresponds  with  the  other  derived  albumins;  it  is  obtainable  as  a  pre- 
cipitate by  neutralizing  milk  with  acid  (acetic).  Naturally  it  is  precipi- 
tated in  sour  milk,  on  the  formation  of  lactic  acid. 

III.  Globulins  which  comprise  the  fibrin-forming  substances  of  the 
blood  and  the  coagulable  material  in  muscle,  and  also  the  principal  part 
of  the  crystalline  lens,  yelk  of  egg,  etc.,  are  soluble  in  very  dilute  saline 
solutions,  but  not  in  distilled  water  like  the  native-albumins;  on  addition 
of  an  acid  or  alkali,  they  are '  converted  into  the  corresponding  derived- 
albumin.  They  are  precipitated  on  heating.  The  following  are  the 
chief  varieties  of  globulins. 

(a.)  Globulin  or  CrijstaUin  is  prepared  by  rubbing  up  the  crystalline 
lens  with  sand,  adding  water  and  filtering.  On  passing  a  current  of  car- 
bonic acid  gas  through  the  filtrate,  globulin  is  precipitated.  In  proper- 
ties, it  resembles  fibrino-plastin  and  fibrinogen,  but  cannot  apparently 
produce  fibrin  in  fluids  containing  either.    It  coagulates  at  70° — 75°  C. 

(b.)  Myosin  can  be  prepared  (1)  from  dead  muscle  by  removing  all 
fat,  tendon,  etc.,  and  washing  repeatedly  in  water,  until  tlie  washing 
contains  no  trace  of  proteids,  and  tlien  treating  Avith  10  per  cent,  solution 
of  sodium  chloride,  whicli  will  dissolve  a  large  i)roportion  into  a  viscid 
fluid,  wliich  filters  witli  difficulty.  If  the  viscid  filtrate  be  drop})ed  little 
by  little  into  a  large  quantity  of  distilled  Avater,  a  white  flocculent  ]u-e- 
cipitate  of  myosin  will  occur.  {'I)  Or  from  living  muscle  by  freezing  and 
rubbing  up  in  ji  mortar  with  snow  and  sodium  chloride  solution  1  ])er 
cent.,  a  fiuid  is  obtained  wliich  on  filtering  is  at  first  liquid,  but  will  finally 
clot;  tlu^  (^lot  is  myosin. 

Myosin,  on  addition  of  dilute  acids,  dissolves  and  forms  syntonin  or 
acid-all)uinin.  It  is  less  soluble  in  dilute  saline  solutions  than  (r)  and 
(d).    It  (coagulates  at  55' —CO"  ( ). 


APPENDIX. 


329 


(c.)  Fihrhioplastin  ov  fihrinoplastic  glohulin  ov  paraglohulin  is  pre- 
pared from  blood-serum  diluted  with  10  vols,  of  water,  by  passing  a  cur- 
rent of  carbonic  acid  gas,  and  collecting  the  fine  precipitate  which  is 
formed,  and  washing  with  water  containing  carbonic  acid  gas.  The 
current  should  be  strong  and  not  long  continued.  It  may  be  better  pre- 
pared as  a  sticky  white  substance,  by  saturating  serum  with  crystallized 
sodium  chloride  or  magnesium  sulphate.  (See  also  p.  69,  Vol.  I.)  It 
coagulates  at  68°— 80°  C. 

(d.)  Fibrinogen  is  prepared  from  hydrocele  and  other  like  fluids  by 
diluting  and  passing  a  brisk  current  of  carbonic  acid  gas  (CO J  through 
the  solution;  or  by  saturation  of  the  nerve  fluids  with  sodium  chloride  or 
magnesium  sulphate.  (See  also  p.  69,  Vol.  I.)  It  coagulates  at  55° — 
57°  C. 

(e.)  VitelUn  can  be  prepared  from  yelk  of  egg,  in  which  it  is  prob- 
ably associated  with  lecithin. 

IV.  Fibrin  is  a  white  filamentous  body  formed  in  the  spontaneous 
coagulation  of  certain  animal  fluids.  It  is  insoluble  in  water,  except  at 
very  high  temperatures,  soluble  in  dilute  acids  and  alkalies  to  a  slight 
degree,  and  in  strong  neutral  saline  solutions.  Soluble  also  in  strong 
acids  and  alkalies. 

It  is  prepared  by  washing  blood-clot  or  by  whipping  blood  with  a 
bundle  of  twigs.  Its  formation  in  the  blood  has  been  already  fully  con- 
sidered. 

V.  Peptones  (or  albuminose)  are  nitrogenous  bodies  of  uncertain 
composition  made  in  the  process  of  the  digestion  of  other  proteids.  It  is 
almost  certain  that  there  are  several  distinct  forms. 

The  great  distinction  which  exists  between  peptone  and  other  proteids 
is  their  diflusibility  and  they  giving  no  precipitates  with  either  acids  or 
alkalies,  with  copper  sulphate,  ferric  chloride,  potassium  ferrocyanide 
and  acetic  acid,  or  on  boiling,  and  only  with  picric  acid,  tannin,  mer- 
curic chloride,  silver  nitrate,  and  lead  acetate.  In  addition  to  this  the 
color  which  a  peptone  gives  with  potassium  hydrate  and  cupric  sulphate 
is  reddish  instead  of  violet. 

Kiihne  believes  that  ordinary  albumin  splits  up  under  the  action  of 
the  gastric  juice  or  pancreatic  juice  into  two  parts,  one  called  antialhu- 
mose,  and  the  other  hemialbumose,  and  further  that  antialbumose  becomes 
antipepfone  and  hemialbumose,  Imnipeptone.  The  difference  between 
hemipeptone  and  antipeptone  is  that  the  former  can  be  further  split  up 
by  the  action  of  the  pancreatic  juice.  He  believes  that  antialbumose  is 
closely  allied  to  syntonin,  and  that  the  hemialbumose  is  more  like  myosin, 
and  if  the  pepsin  be  feebly  acting,  a  body  which  he  calls  ant  i  album  ate 
appears,  which  cannot  be  converted  into  peptone  by  gastric  juice,  but  can 
by  pancreatic  juice.  Solutions  of  hydrochloric  acid  or  of  sulphuric  acid 
can,  under  favorable  circumstances,  partially  change  albumin  into  peptone. 

VI.  — Coagulated  Proteids. — When  a  native  albumin  or  a  globulin 
is  raised  to  a  certain  temperature  (varying  a  little  with  each  substance). 


330  HAND-BOOK  OF  PHYSIOLOGY. 

about  70°  0,  it  undergoes  coagulation  and  loses  most  of  its  original  char- 
acters. It  becomes  insoluble  botb  in  water  and  in  saline  solutions,  and 
although  soluble  in  strong  acids  and  alkalies  in  boiling,  partially  decom- 
poses during  the  process.  They  are  not  soluble  in  dilute  acids  or  alka- 
lies, but  dissolve  freely  under  thei  action  of  the  gastric  or  of  the  pancre- 
atic secretion,  being  converted  into  peptones. 

YII.  Lardacein. — Lardacein  or  amyloid  substance  is  found  in  cer- 
tain organs  of  the  body,  chiefly  in  "the  liver,  as  a  morbid  deposit.  It  is 
insoluble  in  water,  and  in  saline  solutions.  It  is  unacted  upon  by  the 
digestive  juices.  It  is  colored  red  by  iodine.  It  is  soluble  in  acids  or  in 
alkalies,  thus  forming  acid  or  alkali  albumin. 

(2.)  Gelatinous  princijjJes  include: — (1.)  Gelatin;  (2.)  Mucin;  (3.) 
Elastin;  (4.)  Chondrin;  and  (5.)  Keratin.  They  are  very  like  the  Pro- 
teid  group,  but  exhibit  considerable  differences  among  themselves. 

(1.)  Gelatin  is  produced  by  boiling  fibrous  tissue,  or  by  treating  bones 
with  acids,  whereby  their  salts  are  dissolved,  leaving  the  framework  of 
gelatin,  which  is  soluble  in  hot  water. 

It  is  a  yellow,  amorphous,  transparent  body,  which  does  not  give  any 
of  the  proteid  reactions  if  pure,  insoluble  in  cold,  but  soluble  in  hot 
water,  forming  a  jelly  on  cooling.  Its  solutions  are  precipitated  by  tan- 
nin, by  alcohol  and  by  mercuric  chloride. 

(2.)  Mucin,  contained  in  mucus.  It  is  a  substance  of  ropy  consist- 
ency. 

Prepared  from  ox-gall  by  precipitation  with  alcohol,  and  afterward 
redissolving  in  water,  and  reprecipitating  with  acetic  acid.  It  may  be  also 
prepared  from  diluting  mucus  with  water,  filtering,  treating  the  insoluble 
portion  with  weak  caustic  alkali,  and  precipitating  with  acetic  acid.  It 
is  precipitated  by  alcohol  and  mineral  acids,  but  dissolved  by  excess  of 
the  latter — dissolved  by  alkalies.  It  gives  the  proteid  reaction  with  Mil- 
lon^s  reagent,  but  not  with  cupric  sulphate  and  potassium  hydrate.  It  is 
not  precipitated  by  mercuric  chloride  or  by  tannic  acid.  It  is  a  colloid 
substance. 

(3.)  Elastin  is  the  basis  of  elastic  tissue;  it  is  soluble  only  in  strong 
alkalies  on  boiling;  strong  sulphuric  or  nitric  acid  dissolves  it  in  the  cold. 

(4.)  Cliondrin  is  contained  in  the  matrix  of  hyaline  cartilage,  and 
may  be  extracted  by  boiling  with  water  and  precipitating  with  acetic 
acid. 

(5.)  Keratin  is  obtained  from  hair,  nails,  and  dried  skin.  It  contains 
sulphur,  evidentl}'  only  loosely  combined. 

(3.)  Decomposition  Nit rogeno%iS  products. — These  are  formed  by  tlie 
chemical  actions  which  go  on  in  digestion,  secretion,  and  nutrition. 

^lost  of  the  compounds  are  amides,  wliich  are  acids  in  which  amidof/en, 
NII^,  is  sul)stituted  for  liydroaiil,  OH.  Amides  may  also  be  represented 
as  obtained  from  tlie  ammonium  salts  by  a1)straction  of  water,  or  as  de- 
rived from  one  or  more  molecules  of  ammonia,  NII3,  by  substituting 
acid  radi(tals  for  liydrogen.  Tims  aceta/nide  may  be  written  in  any  of 
the  following  ways: — 


APPENDIX. 


331 


CH3 

CO  NH.3 


CH3 

CO  ONli 


or 


(C,  H,0)' 


(C2  H3  0)  being  the  radical  of  acetic  acid. 

Varieties. — Several  of  the  varieties  of  amides  are  represented  in  the 
products  with  which  we  have  to  do. 

(a.)  Monamides  which  are  derived  from  a  monatomic  acid — that  is  to 
say,  an  acid  which  contains  the  carboxyl  group  CO  OH,  once,  by  the  sub- 
stitution of  NH^  for  OH  in  this  group.  In  these  compounds  if  only  one 
is  the  H  in  NHg  is  replaced  by  an  acid  radical,  a  primary  monamide  of 
formed;  if  two,  by  acid  or  alcohol  radicals,  a  secondary  monamide;  if 
three,  by  acid  or  alcohol  radicals,  a  tertiary  monamide. 

Two  monamides  are  also  formed  from  each  diatomic  acid  {i.e.,  those 
which  contain  OH  twice,  once  in  the  carboxyl  group  CO  OH,  and  once  in 
the  alcohol  group  Cn  H^n  OH),  both  by  the  substitution  of  NH^  for  OH, 
and  therefore  having  the  same  composition.  They  are  isomeric  and  not 
identical  however,  the  one  formed  by  the  substitution  of  NH^  for  the  alco- 
holic OH  being  acid,  while  the  other  formed  by  the  replacement  of  the 
basic  hydroxyl  is  neutral.  The  acid  amides  are  called  amic  acids,  or  may 
form  a  class  by  themselves,  called  alanines. 

Three  amides  are  obtained  from  each  diatomic  and  bibasic  acid: — (1.) 
An  acid  amide  or  amic  acid,  derived  from  the  acid  ammonium  salt  by  ab- 
straction of  one  molecule  of  water.  (2.)  A  neutral  monamide  (or  imide), 
derived  by  abstraction  of  two  molecules  of  water  from  the  ammonium 
salts.  (3.)  A  neutral  amide  or  (b)  Diamide,  derived  from  the  ammonium 
salt  by  abstraction  of  two  molecules  of  water.  Thus  succinic  acid  gives: — 


the  biliary  acids,  never  free.  Glycocholic  acid,  when  treated  with  weak 
acids,  with  alkalies,  or  with  baryta  water,  splits  up  into  cholic  acid  and 
glycin,  or  amido-acetic  acid.  Thus:  C^^  H,3  NO^  +  H,0  =  C^p  H,„  0^ 
+  C2  Hg  NO^.  Glycocholic  acid  +  water  —  cholic  acid  -\-  glycin,  and 
under  similar  circumstances  Taurocholic  acid  splits  up  into  cholic  acid 


and  tauriii:-C„  H„  0,  NSO,  +  H,0  =  C,.  H„  0,  +  0,  H,  NSO„  or 


amido-isethionic.  Taurocholic  acid  +  water  =  cholic  acid  and  taurin. 
Glycin  occurs  also  in  hippuric  acid.  It  can  be  prepared  from  gelatin  by 
the  action  of  acids  or  alkalies;  it  can  also  be  obtained  from  hippuric  acid. 


Succinamide  . 


Succinamic  Acid 


Succinimide 


{a)  Pkimaey  Mon"amides. 
Glycin,  glycocol  or  glycocin,  or  amido-acetic  acid — 


occurs  in  the  body  in  combination,  as  in 


332 


HAND-BOOK  OF  PHYSIOLOaY. 


Leucin,   or  amido-caproic  acid,   H  r  0      or   ^jj    j-  0 

occurs  normally  in  many  organs  of  the  body  and  is  a  product  of  the  pan- 
creatic digestion  of  proteids.  It  is  present  in  the  urine  in  certain  diseases 
of  the  liver  in  which  there  is  loss  of  substance,  especially  in  acute  yellow 
atrophy.  It  occurs  in  circular  aily  discs  or  crystallizes  in  plates,  and  can 
be  prepared  either  by  boiling  horn  shavings,  or  any  of  the  gelatins,  with 
sulphuric  acid,  or  out  of  the  products  of  pancreatic  digestion. 

H,  0, 1 

Sarcosin  may  be  considered  as  methyl  glycin,    CHg      V  N.    It  is  a 

constituent  of  kreatin,  but  has  never  been  found  free  in  the  human  body. 

Neurin  (C^  H^g  NO),  is  an  unstable  body,  which  has  been  found  in 
ox  and  pig's  gall. 

Taurin,  C  H,NSO,  or  SO,  HO  >  N;  or  amido-isethionio  acid,  is  a  con- 

stituent  of  the  bile  acid,  taurocholic  acid,  and  is  found  also  in  traces  in 
the  muscles  and  lungs. — See  above. 

Cystin,  C3  NSO^  occurs  in  a  rare  form  of  urinary  calculus,  which 
is  only  formed  in  a  urine  of  neutral  reaction.  It  can  be  crystallized  in 
hexagonal  laminae  of  pale  yellow  color,  becoming  greenish  on  exposure 
to  light. 

C,H,N03,  orC,H3  0J 
Hippuric  Acid,  O^H^O  >  N,*or  benzolglycin,  a  normal 

H  ) 

constituent  of  human  urine,  the  quantity  excreted  being  increased  by  a" 
vegetable  diet,  and  therefore  it  is  present  in  greater  amount  in  the  urine 
of  herbivora.  It  may  be  decomposed  by  acids  into  glycin  and  benzoic 
acid.  It  crystallizes  in  semi-transparent  rhombic  prisms,  almost  insoluble 
in  cold  water,  soluble  in  boiling  water.    (See  also  p.  361,  Vol.  I.) 

Tyrosin,  0^  H,j  NO3,  is  found,  generally  together  with  leucin,  in 
certain  glands,  e.g.,  pancreas  and  spleen;  and  chiefly  in  the  products  of 
pancreatic  digestion  or  of  the  putrefaction  of  proteids.  It  is  found  in 
the  urine  in  some  diseases  of  the  liver,  especially  acute  yellow  atrophy. 
It  crystallizes  in  fine  needles,  which  collect  into  feathery  masses.  It  gives 
the  proteid  test  with  Millon's  reagent,  and  heated  with  strong  sulphuric 
acid,  on  the  addition  of  ferric  chloride  gives  a  violet  color. 

Lecithin,  0,^  H^^  P  NO,,,  is  a  phosphoretted  fatty  body,  whicli  has 
been  found  mixed  with  cerebrin,  and  oleophosphoric  acid  in  the  brain. 
It  is  also  found  in  blood,  bile  and  serous  fluids,  and  in  larger  quantities  in 
nerves,  pus,  yolk  of  egg,  semen,  and  white  blood-corpuscles.  On  boiling 
with  acids  it  yields  cholin,  glycero-])h()s})lioric  acid.  ])alnii('  and  oleic  acids. 

Cerebrin,  C,^  If,,^  NO,,  is  found  in  nerves,  pus-('ori)usclos,  and  in  the 
brain.  Its  chemical  constitution  is  not  known.  It  is  a.  light  anior))hous 
powder,  tasteless  and  odorless.  Swells  up  like  starch  when  boiled  with 
water,  and  is  converted  by  acids  into  a  saccharine  substance  and  other 
bodies.    The  so-called  ProtiKjoit  is  a  mixture  of  lecithin  and  cerebrin. 


APPENDIX. 


333 


(b.)  Primaey  Diamides  or  Ureas. 

Urea,  (NHJ^  CO,  is  the  last  product  of  the  oxidation  of  the  albu- 
minous tissues  of  the  body  and  of  the  albuminous  foods.  It  occurs  as 
the  chief  nitrogenous  constituent  of  the  urine  of  man,  and  of  some  other 
animals.  It  has  been  found  in  the  blood  and  serous  fluids,  lymph,  and 
in  the  liver. 

Properties.  Crystallizes  in  thin  glittering  needles,  or  in  prisms  with 
pyramidal  ends.  Easily  soluble  in  water  and  alcohol,  insoluble  in  ether, 
easily  decomposed  by  strong  acids,  readily  forms  compounds  with  acids 
and  bases,  of  which  the  chief  are  (NHJ^  COHNO3,  urea  nitrate,  and 
(NHJ,  (00),  H,  0,  0,  +  H,  0,  urea  oxalate. 

Constitution. — It  is  usually  considered  to  be  a  diamide  of  carbonic 
00  N  H J 

acid  which  may  be  written       N^,  or  00  N      >■  which  is  CO  (HO)^, 

H,  ) 
with  (OH) '2,  replaced  by  (NH,)',-   Some  think  it  a  monamide  of  carbamic 
acid,  00,  OH,  NH„  thus  CO,  NH,  NH„  with  one  atom  of  NH,,  or 
amidogen  in  place  of  one  of  hydroxyl  OH. 

Urea  is  isomeric  with  ammonium  cyanate  C  j-  Qjv^g;  from  which  it 
was  first  artificially  prepared. 

Kreatin,  C^  Hg  Ng  0,,  is  one  of  the  primary  products  of  muscular 
disintegration.  It  is  always  found  in  the  juice  of  muscle.  It  is  gener- 
ally decomposed  in  the  blood  into  urea  and  kreatinin,  and  seldom,  unless 
under  abnormal  circumstances,  appears  as  such  in  the  urine.  Treated 
with  either  sulphuric  or  hydrochloric  acid,  it  is  converted  into  kreatinin; 
thus — 

C,  H,  N3  0,  =  0,  H,  N3  0  +  H,  0. 

Kreatinin,  0^  H,  is  present  in  human  urine,  derived  from  oxi- 
dation of  kreatin.    It  does  not  appear  to  be  present  in  muscle. 


(c.)  Ureides. 

Ureides  are  a  third  variety  of  amides,  and  may  be  considered  as  ureas 
in  which  part  of  the  hydrogen  is  replaced  by  diatomic  acid  radicals. 
Monoureides  contain  one  acid  radical  and  one  urea  residue;  and  diureides, 
one  acid  radical  and  two  urea  residues. 

Uric  Acid,  C  H,  0  3,  occurs  in  the  urine,  sparingly  in  human  urine, 
abundantly  in  that  of  birds  and  reptiles,  where  it  represents  the  chief, 
nitrogenous  decomposition  product.  It  occurs  also  in  the  blood,  spleen, 
liver,  and  sometimes  is  the  only  constituent  of  urinary  calculi.  It  is 
probably  converted  in  the  blood  into  urea  and  some  carbon  acid.  It 


334 


HAND-BOOK  OF  PHYSIOLOGY. 


generally  occurs  in  nrine  in  combination  with  bases,  forming  urates, 
and  never  free  unless  under  abnormal  conditions.  A  deposit  of  urates 
may  occur  when  the  urine  is  concentrated  or  extremely  acid,  or  when, 
as  during  febrile  disorders,  the  conversion  of  uric  acid  into  urea  is  incom- 
pletely performed. 

Properties. — Crystallizes  in  many  forms,  of  which  the  most  common 
are  smooth,  transparent,  rhomboid  plates,  diamond-shaped  plates,  hexa- 
gonal tables,  etc.  Very  insoluble  in  water,  and  absolutely  so  in  alcohol 
and  ether.  Dried  with  strong  nitric  acid  in  a  water-bath,  a  compound 
is  formed  called  alloxan,  which  gives  a  beautiful  violet  red  with  ammo- 
nium hydrate  (murexide),  and  a  blue  color  with  potassium  hydrate.  It 
is  easily  precipitated  from  its  solutions  by  the  addition  of  a  free  acid.  It 
forms  both  acid  and  neutral  salts  with  bases.  The  most  soluble  urate  is 
lithium  urate. 

Composition. — Very  uncertain;  has  been  however  recently  produced 
artificially,  but  it  is  not  easily  decomposed;  it  may  be  regarded  as  diureide 
of  tartronic  acid.    The  chief  product  of  its  decomposition  is  urea. 

Guanin,  0,  has  been  found  in  the  human  liver,  spleen,  and 

faeces,  but  does  not  occur  as  a  constant  product. 

Xantliin,  0^,  has  been  obtained  from  the  liver,  spleen, 

thymus,  muscle,  and  the  blood.  It  is  found  in  normal  urine,  and  is  a 
constituent  of  certain  rare  urinary  calculi. 

Hypoxantliin,  0,  or  sarMn,  is  found  in  juice  of  flesh,  in  the 

spleen,  thymus,  and  thyroid. 

Allantoin,  0^  Hg  0,,  found  in  the  allantoic  fluid  of  the  foetus,  and 
in  the  urine  of  animals  for  a  short  period  after  their  birth.  It  is  one  of 
the  oxidation  products  of  uric  acid,  which  on  oxidation  gives  urea. 

In  addition  to  the  amides  and  probably  related  to  them,  are  certain 
coloring  and  excrementitious  matters,  which  are  also  most  likely  distinct 
decomposition  compounds. 

Pigments,  etc. 

Bilirubin,  OgHgNO^,  is  the  best  known  of  the  bile  pigments.  It  is  best 
made  by  extracting  inspissated  bile  or  gall  stones  with  water  (which 
dissolves  the  salts,  etc.),  then  with  alcohol,  which  takes  out  cholesterin, 
fatty,  and  biliary  acids.  Hydrochloric  acid  is  then  added,  which  decom- 
poses the  lime  salt  of  bilirubin  and  removes  the  lime.  After  extracting 
with  alcohol  and  ether,  tlie  residue  is  dried  and  finally  extracted  with 
cliloroform.  It  crystallizes  of  a  bluish-red  color.  It  is  allied  in  compo- 
sition to  haematin. 

Hiliverdi^i,  OJTgNO^,  is  made  by  passing  a  current  of  air  through 
an  alkaline  solution  of  bilirubin,  and  by  precipitation  with  hydrochloric 
acid.    It  is  a  groon  pigment. 

Bilifiisciii,  CgII,,NOa,  is  made  by  treating  gall  stones  with  ether,  then 
with  dilute  acid,  and  extracting  with  absolute  alcohol.  It  is  a  nou-crys- 
tallizablc  brown  ])igment. 


APPENDIX. 


335 


Bilijnasin  is  a  pigment  of  a  green  color,  which  can  be  obtained  from 
gall  stones. 

Bilihumin  (Staedeler)  is  a  dark  brown  earthy-looking  substance,  of 
which  the  formula  is  unknown. 

Urobilin  occurs  in  bile  and  in  urine,  and  is  probably  identical  with 
stercobiliii,  which  is  found  in  the  faeces. 

Uroerythrin  is  one  of  the  coloring  matters  of  the  urine.  It  is  orange 
red,  and  contains  iron. 

Melanin  is  a  dark  brown  or  black  material  containing  iron,  occurring 
in  the  lungs,  bronchial  glands,  the  skin,  hair,  and  choroid. 

Hcematin  has  been  fully  treated  of  in  Chapter  IV. 

Indican  is  supposed  to  exist  in  the  sweat  and  urine.  It  has  not,  how- 
ever, been  satisfactorily  isolated. 

Indigo,  Cg  0,  is  formed  from  indican,  and  gives  rise  to  the 

bluish  color  which  is  occasionally  met  with  in  the  sweat  and  urine. 

Indol,  Cp  N,  is  found  in  the  faeces,  and  is  formed  either  by  decom- 
position of  indigo,  or  of  the  proteid  food  materials.  It  gives  the  charac- 
teristic disagreeable  smell  to  faeces. 

(4.)  Nitrogenous  Bodies  of  Uncertain  Nature, 

Ferments  are  bodies  which  possess  the  property  of  exciting  chemical 
changes  in  matter  with  which  they  come  in  contact.  They  are  at  present 
divided  into  two  classes,  called  (1)  organized,  and  (2)  unorganized  or 
soluble.  (1.)  Ot  the  organized,  yeast  may  be  taken  as  an  example.  Its 
activity  depends  upon  the  vitality  of  the  yeas^  cell,  and  disappears  as  soon 
as  the  cell  dies,  neither  can  any  substance  be  obtained  from  the  yeast 
by  means  of  precipitation  with  alcohol  or  in  any  other  way  which  has  the 
power  of  exciting  the  ordinary  change  produced  by  yeast. 

(2.)  Unorganized  or  soluble  ferments  are  those  which  are  found  in 
secretions  of  glands,  or  are  produced  by  chemical  changes  in  animal  or 
vegetable  cells  in  general;  when  isolated  they  are  colorless,  tasteless, 
amorphous  solids  soluble  in  water  and  glycerin,  and  precipitated  from  the 
aqueous  solutions  by  alcohol  and  acetate  of  lead.  Chemically  many  of 
these  are  said  to  contain  nitrogen. 

Mode  of  action. — Without  going  into  the  theories  of  how  these  unor- 
ganized ferments  act,  it  will  suffice  to  mention  that: 

(1.)  Their  activity  does  not  depend  upon  the  actual  amount  of  the 
ferment  present.  (2.)  That  the  activity  is  destroyed  by  high  tempera- 
ture, and  various  concentrated  chemical  reagents,  but  increased  by 
moderate  heat,  about  40°  C.  and  by  weak  solutions  of  either  an  acid  or 
an  alkaline  fluid.  (3.)  The  ferments  themselves  appear  to  undergo  no 
change  in  their  own  composition,  and  waste  very  slightly  during  the 
process. 

Varieties. — The  chief  classes  of  unorganized  ferments  are: — 

(1.)  Amylolytic,  which  possess  the  property  of  converting  starch  into 


HAND-BOOK  OF  PHYSIOLOGY. 


glucose.  They  add  a  molecule  of  water,  and  may  be  called  hydrolytic. 
The  probable  reaction  is  as  follows: 

3  C,       O3  +  3  H,,  =  C,  H,,  0,  +  0,       O,  =  3  C,  H,,  0, 
Starch         Water        Glucose  Dextrin  Glucose. 

This  shows  that  there  is  an  intermediate  reaction,  the  starch  being 
first  turned  only  partly  into  glucose  and  principally  into  dextrin,  which 
is  afterward  further  converted  into  glucose.  The  principal  amylolytic 
ferments  are  Ptyalin,  found  in  the  saliva,  and  a  ferment,  probably  dis- 
tinct in  the  pancreatic  juice,  called  Amyloimn.  These  both  act  in  an 
alkaline  medium.  Amylolytic  ferments  have  been  found  in  the  blood 
and  elsewhere. 

Conversion  of  starch  info  sugar. — With  reference  to  the  action  of  the 
amylolytic  ferments,  recent  observations  have  shown  that  the  starch  mole- 
cule is  not  by  any  means  so  simple  as  it  has  been  represented  above.  As 
it  is  said  that  starchy  materials,  in  the  form  of  wheat  and  other  cereals, 
and  in  the  potato  or  its  substitutes,  form  two-thirds  of  the  total  food  of 
man,  it  is  very  important  that  we  should  note  (1)  the  changes  which 
occur  in  starch  on  cooking,  and  (2)  the  series  of  reactions  it  undergoes 
during  its  conversion  by  the  amylolytic  ferments  into  sugar. 

(1.)  The  object  of  this  change  is  to  produce  gelatinous  or  soluble 
starch.  A  starch  granule  consists  of  two  parts:  an  envelope  of  cellulose, 
which  gives  a  blue  color  with  iodine  on  addition  of  sulphuric  acid,  and  of 
granulose,  which  is  contained  within  it,  giving  a  blue  with  iodine  alone. 
Briicke  states  that  a  third  body  is  contained  in  the  granule,  which  gives 
a  red  with  iodine,  viz.,  erytliro-granulose.  On  boiling,  the  granulose 
sw^ells  up,  bursts  the  envelope,  and  the  whole  granule  is  more  or  less 
completely  converted  into  a  paste  or  into  mucilaginous  gruel. 

(2.)  Changes  which  occur  on  addition  of  an  amylolytic  ferment.  On 
the  addition  of  saliva  or  extract  of  pancreas  to  gelatinous  starch,  the  first 
change  noticed  is  that  the  paste  liquifies  very  quickly,  but  the  liquid  does 
not  give  the  reaction  for  dextrin  or  for  sugar;  but  soon  this  latter  reaction 
appears,  increasing  very  considerably  and  quickly,  although  at  first,  in 
addition,  a  reaction  of  erethrodextrin,  a  red  on  addition  of  iodine,  is 
found;  as  the  sugar  increases,  however,  this  disappears.  At  first  the 
erythrodextrin  is  mixed  with  starch,  as  the  reaction  is  a  reddish  purple 
witli  iodine,  then  it  is  a  pure  red,  and  finally  a  yellowish  brown.  As  the 
sugar  continues  to  increase  the  reaction  with  iodine  disappears,  but  it  is 
said  that  dextrin  is  still  present  in  the  form  of  achroo-dextrines.  which 
give  no  reaction  witli  iodine.  However  long  the  reaction  goes  on,  it  is 
unlikely  that  all  the  dextrin  becomes  sugar. 

Next  with  regard  to  the  kind  of  sugar  formed,  it  is,  at  first  at  any 
rate,  not  glucose  but  maltose,  the  formula  for  which  is  Cj,  H^^  ^u-  Maltose 
is  allied  to  saccharose  or  cane  sugar  more  nearly  than  to  glucose;  it  is 
crystalline;  its  solution  has  the  i)ropert3'  of  polarizing  light  to  a  greater 
degree  tlian  solutions  of  glucose;  is  not  so  sweet,  and  reduces  copper 
sulphate  less  easily.  It  can  be  converted  into  glucose  by  boiling  with 
dilute  acids. 

According  to  Brown  and  Heron  the  reactions  may  be  represented 
thus: — 


APPENDIX. 


337 


One  molecule  of  gelatinous  starch  is  converted  into  n  molecules  of 
soluble  starch. 

One  molecule  of  soluble  starch^lO  (C,,        0,  J+8  (H,  0) 
=  1  Erythro-dextrin  (mvinsr  red  with  iodide)  Maltose. 

9(C„H,„0J  +(0,H„OJ 
=  2.  Erythro-dextrin  (living  yellow  with  iodine)  Maltose. 

8  (C,,H,.C.,)  +  3  (0.,  H„  C„) 

=  3.  Achroo-dextrin  Maltose. 

7  (C„  H,.  0„)  +  3  (C„  H,,  0„) 

And  so  on;  the  resultant  being: — 

10  (C.,  H,„  0..)  +  8  (H,  0)  =  8  (0„  H,,  0„)  +  3  (C,,  H,.  0,J 

Soluble  starch  Water  Maltose  Achroo-dextrin. 

Pancreatic  juice  and  intestinal  juice  are  able  to  turn  the  achroo-dex- 
trin which  remains  into  maltose,  and  maltose  into  glucose  (dextrose). 
It  is  doubtful  whether  saliva  possesses  the  same  power. 

(2.)  Proteolytic  convert  proteids  into  peptones.  The  nature  of  their 
action  is  probably  hydrolytic.  The  proteolytic  ferments  of  the  body  are 
called  Pepsin,  acting  in  an  acid  medium  from  the  gastric  juice.  Trypsin, 
acting  in  an  alkaline  medium  from  the  pancreatic  juice.  The  Succus 
entericus  is  said  to  contain  a  third  such  ferment. 

(3.)  Inversive,  which  convert  cane  sugar  or  saccharose  into  grape 
sugar  or  glucose.  Such  a  ferment  was  found  by  Claude  Bernard  in  the 
Succus  entericus;  and  probably  exists  also  in  the  stomach  mucus. 

3  0„  H,,  0„  +  2  H,  0  =  C,,  H„  0„  +  0„  H„  0., 

Saccharose         Water  Dextrose  Lsevulose, 

(4.)  Ferments  wliicTi  act  upon  fats;  such  a  body  called  Bteapsin  has 
been  found  in  pancreatic  juice. 

The  ferments  Amylopsin,  Trypsin,  and  Bteapsin,  are  said  to  exist 
separately  in  pancreatic  juice,  and  if  so,  make  up  what  was  formerly  called 
Pancreatin  and  which  was  said  to  have  the  functions  of  the  three. 

(5.)  Milh-curdling  ferments.  It  has  been  long  known  that  rennet,  a 
decoction  of  the  fourth  stomach  of  a  calf,  in  brine,  possessed  the  power  of 
curdling  milk.  This  power  does  not  depend  upon  the  acidity  of  the  gas- 
tric juice,  since  the  curdling  will  take  place  in  a  neutral  or  alkaline 
medium;  neither  does  it  depend  upon  the  pepsin,  as  pure  pepsin  scarcely 
curdles  milk  at  all,  and  the  rennet  which  rapidly  curdles  milk  has  a  very 
feeble  proteolytic  action.  From  this  and  other  evidence  it  is  believed 
that  a  distinct  milk-curdling  ferment  exists  in  the  stomach.  W.  Roberts, 
has  shown  that  a  similar  but  distinct  ferment  exists  in  pancreatic  extract, 
which  acts  best  in  an  alkaline  medium,  next  best  in  an  acid  medium, 
and  worst  in  a  neutral  medium.  The  ferment  of  rennet  acts  best  in  an 
acid  medium,  and  worst  in  an  alkaline,  the  reaction  ceasing  if  the  alka- 
linity be  more  than  slight. 
Vol.  II.— 22. 


338 


HAND-BOOK  OF  PHYSIOLOGY. 


In  addition  to  the  above  ferments,  many  others  most  likely  exist  in  the 
body,  of  which  the  following  are  the  most  important : 

6.  Fibrin-forming  ferment  (Schmidt),  (see  p.  69,  et  seq.,  Vol.  I.) 
found  in  the  blood,  lymph  and  chyle. 

7.  A  ferment  which  converts  glycogen  into  glucose  in  the  liver;  being 
therefore  an  amylolytic  ferment. 

8.  Urinary  ferments. 

(&.)  Organic  non-nitrogenous  lodies  consist  of — (1.)  Oils  and  fats. 
(2.)  Amyloids.    (3.)  Acids. 

(1.)  Oils  and  Fats. 

Saponifiable.  Non-saponifiable. 

Palmitin   C),,H,„  0^  Cholesterin  ....    0,„H,,  0 

Stearin   O^^H^^O^  Stercorin  ? 

Olein     ......  C,,H:o40e  Excretin  0,,H,,„SO, 

Constitution, 

The  Saponifialle  fats  are  formed  by  the  union  of  fatty  acid  radicals 
with  the  triatomic  alcohol.  Glycerin  O3  (OH)g.  The  radicals  are  0^^ 
H35O,  Hjg  0,  and  O^g  H^g  0,  respectively.  Human  fat  consists  of  a 
mixture  of  palmitin^  stearin,  and  olein,  of  which  the  two  former  con- 
tribute three-quarters  of  the  whole.    Olein  is  the  only  liquid  constituent. 

General  characteristics. — Insoluble  in  water  and  in  cold  alcohol;  sol- 
uble in  hot  alcohol,  ether,  and  chloroform.  Colorless  and  tasteless;  easily 
decomposed  or  saponified  by  alkalies  or  superheated  steam  into  glycerin 
and  the  fatty  acids. 

Non-8aponifiaUe. — Cholesterin,  C^g  H^^  O,  is  the  only  alcohol  which 
has  been  found  in  the  body  in  a  free  state.  It  occurs  in  small  quantities 
in  the  blood  and  various  tissues,  and  forms  the  principal  constituent  of 
gall-stones.  It  is  found  in  dropsical  fluids,  especially  in  the  contents  of 
cysts,  in  disorganized  eyes,  and  in  plants  (especially  peas  and  beans).  It 
is  soluble  in  ether,  chloroform,  or  benzol.  It  crystallizes  in  white  feathery 
needles.    See  also  under  the  head  of  the  constituents  of  the  bile. 

Excretin  (Marcet),  and  Stercorin  (Flint),  are  crystalline  fatty  bodies 
which  have  been  isolated  from  the  faeces. 

(2.)  Amyloids. 

Amyloids. — Under  this  head  are  included  both  starch  and  sugar.  The 
substances,  like  the  fats,  contain  carbon,  hydrogen,  and  oxygen;  but  the 
last-named  element  is  present  in  mucli  larger  relative  amount,  the  hydro- 
gen and  oxygen  being  in  the  proportion  to  form  water. 

The  following  varieties  of  these  substances  are  found  iu  health  in  the 
body. 


APPENDIX. 


339 


(a)  Glycogen  (C^  H^^  0  J. — This  substance,  which  is  identical  in  com- 
position with  starch,  and  like  it,  is  readily  converted  into  sugar  by  fer- 
ments, is  found  in  many  embryonic  tissues  and  in  all  new  formations 
where  active  cell-growth  is  proceeding.  It  is  present  also  in  the  pla- 
centa.   After  birth  it  is  found  almost  exclusively  in  the  liver  and  muscles. 

Glycogen  is  formed  chiefly  from  the  saccharine  matters  of  the  food; 
but  although  its  amount  is  much  increased  when  the  diet  largely  consists 
of  starch  and  sugar,  these  are  not  its  only  source.  It  is  still  formed 
when  the  diet  is  flesh  only,  by  the  decomposition,  probably,  of  albumin 
into  glycogen  and  urea. 

The  destination  of  glycogen  has  been  considered  in  a  former  chapter. 
(See  p.  282,  Vol.  1.) 

(i)  Glucose  or  grape  sugar  (Cg  H^^  0^  -f-  0)  is  found  in  minute 
quantities  in  the  blood  and  liver,  and  occasionally  in  other  parts  of  the 
body.  It  is  derived  directly  from  the  starches  and  sugars  in  the  food,  or 
from  the  glycogen  which  has  been  formed  in  the  body  from  these  or  other 
matters.  However  formed,  it  is  in  health  quickly  burnt  off  in  the  blood 
by  union  with  oxygen,  and  thus  helps  in  the  maintenance  of  the  body's 
temperature.    Like  other  amyloids  it  is  one  source  whence  fat  is  derived. 

(c)  Lactose  or  sugar  of  milk  (C^^  0„  +  0),  is  formed  in  large 
quantity  when  the  mammary  glands  are  in  a  condition  of  physiological 
activity, — human  milk  containing  5  or  6  per  cent,  of  it.  Like  other 
sugars  it  is  a  valuable  nutritive  material,  and  hence  is  only  discharged 
from  the  body  when  required  for  the  maintenance  of  the  offspring.  The 
same  remark  is  applicable  to  the  other  organic  nutrient  constituents  of 
the  milk,  albumin  and  saponifiable  fats,  which,  if  we  except  what  is 
present  in  the  secretions  of  the  generative  organs,  are  discharged  from 
the  body  only  under  the  same  conditions  and  in  the  same  secretion. 

(d)  Inosite  (CgHj^  Og  +  2  0),  a  variety  of  sugar,  identical  in  com- 
position with  glucose,  but  differing  in  some  of  its  properties,  is  found 
constantly  in  small  amount  in  muscle,  and  occasionally  in  other  tissues. 
Its  origin  and  uses  in  the  economy  are,  presumably,  similar  to  those  of 
glycogen. 

(e)  Maltose  (0^^  H^^  0„),  is  formed  in  the  conversion  of  starch  into 
glucose  (see  p.  336,  Vol.  II.). 

(3.)  Organic  Acids. 


Formic  . 
Acetic  . 
Propionic 
Butyric 
Valerianic 


Group  I. — Monatomic  Fatty  Acids. 


HO  OH 
H„  0  OH 
0  OH 
,  0  OH 
C:  H  0  OH 


0 
C.  H 


Caproic 
Oapric 
Palmitic 
Stearic 
Oleic  . 


Cg  H„  0  OH 
C,  H^,  OOH 
C^g  H3^  0  OH 
C,,  H3.  O  OH 
H  ;  0  OH 


340 


HAND-BOOK  OF  PHYSIOLOGY. 


Formic,  acetic,  and  propionic  acids  are  present  in  sweat,  but  normally 
in  no  other  human  secretion.  They  have  been  found  elsewhere  in  dis- 
eased conditions.  Butyric  acid  is  found  in  sweat.  Various  others  of 
these  acids  have  been  obtained  from  blood,  muscular  juice,  faeces,  and 
urine. 

« 

Group  II. — Diatomic  Fatty  Acids. 


Glycolic 

Lactic 

Leucic 


Monobasic. 


^3  6 

0.  H„  0, 


Oxalic  . 
Succinic 
Sebacic  . 


Bibasic. 


0.  H,0. 
0,  H.  O. 
C..  H.„0. 


Lactic  acid  exists  in  a  free  state  in  muscular  plasma,  and  is  increased 
in  quantity  by  muscular  contraction,  is  never  contained  in  healthy  blood, 
and  when  present  in  abnormal  amount  seems  to  produce  rheumatism. 

Oxalates  are  present  in  the  urine  in  certain  diseases,  and  after  drink- 
ing certain  carbonated  beverages,  and  after  eating  rhubarb,  etc. 


Aeomatic  Series. 

Benzoic  0,  0, 

Phenol  0 

Benzoic  acid  is  always  found  in  the  urine  of  herbivora,  and  can  be 
obtained  from  stale  human  urine.    It  does  not  exist  free  elsewhere. 

Phenol. — Phenyl  alcohol  or  carbolic  acid  exists  in  minute  quantity  in 
human  urine.  It  is  an  alcohol  of  the  aromatic  series. 


2.  In"organic  Peikciples. 

The  inorganic  proximate  principles  of  the  human  body  are  numerous. 
They  are  derived,  for  the  most  part,  directly  from  food  and  drink,  and 
pass  through  the  system  unaltered.  Some  are,  however,  decomposed  on 
their  way,  as  chloride  of  sodium,  of  which  only  four-fifths  of  the  quantity 
ingested  are  excreted  in  the  same  form;  and  some  are  newly  formed 
within  the  body, — as  for  example,  a  part  of  the  sulphates  and  carbonates, 
and  some  of  the  water. 

Much  of  the  inorganic  saline  matter  found  in  the  body  is  a  necessary 
constituent  of  its  structure, — as  necessary  in  its  way  as  albumin  or  any 
other  organic  principle;  another  part  is  important  in  regulating  or  modify- 
ing various  physical  processes,  as  absorption,  solution,  and  the  like  J  while 
a  part  must  be  reckoned  only  as  matter,  which  is,  so  to  speak,  accident- 
ally present,  whether  derived  from  the  food  or  the  tissues,  and  which 
will,  at  the  first  opportunity,  be  excreted  from  the  body. 

Gases. — The  guseous  matters  found  in  the  body  are  Oxygen^  Hydro- 


APPENDIX. 


341 


gen,  Nitrogeriy  Carluretted  and  Sulphuretted  hydrogen^  and  Carbonic 
acid.  The  first  three  have  been  referred  to  (p.  325,  Vol.  II.).  Car- 
buretted  and  sulphuretted  hydrogen  are  found  in  the  intestinal  canal. 
Carbonic  acid  is  present  in  the  blood  and  other  fluids,  and  is  excreted  in 
large  quantities  by  the  lungs,  and  in  very  minute  amount  by  the  skin. 
It  will  be  specially  considered  in  the  chapter  on  Respiration. 

Water,  the  most  abundant  of  the  proximate  principles,  forms  a  large 
proportion, — more  than  two-thirds  of  the  weight  of  the  whole  body.  Its 
relative  amount  in  some  of  the  principal  solids  and  fluids  of  the  body  is 
shown  in  the  following  table  (quoted  by  Dalton,  from  Robin  and  Ver- 
deiFs  table,  compiled  from  various  authors) : — 

Quantity  of  Water  ik  1000  Parts. 


Teeth   100 

Bones   130 

Cartilage   550 

Muscles   750 

Ligament  •    .  768 

Brain   789 

Blood    ........  795 

Synovia   805 


Bile   880 

Milk    887 

Pancreatic  juice   900 

Urine   936 

Lymph   960 

Gastric  juice   975 

Perspiration   986 

Saliva   995 


Uses  of  the  Water  of  the  Body.— The  importance  of  water  as  a 
constituent  of  the  animal  body  may  be  assumed  from  the  preceding  table, 
and  is  shown  in  a  still  more  striking  manner  by  its  withdrawal.  If  any 
tissue — as  muscle,  cartilage,  or  tendon — be  subjected  to  heat  sufficient  to 
drive  off  the  greater  part  of  its  water,  all  its  characteristic  physical  prop- 
erties are  destroyed;  and  what  was  previously  soft,  elastic,  and  flexible, 
becomes  hard  and  brittle,  and  horny,  so  as  to  be  scarcely  recognizable. 

In  all  the  fluids  of  the  body — blood,  lymph,  etc.,  water  acts  the  part 
of  a  general  solvent,  and  by  its  means  alone  circulation  of  nutrient  matter 
is  possible.  It  is  the  medium  also  in  which  all  fluid  and  solid  aliments  are 
dissolved  before  absorption,  as  well  as  the  means  by  which  all,  except 
gaseous,  excretory  products  are  removed.  All  the  various  processes  of 
secretion,  transudation,  and  nutrition,  depend  of  necessity  on  its  presence 
for  their  performance. 

Source. — The  greater  part,  by  far,  of  the  water  present  in  the  body 
is  taken  into  it  as  such  from  without,  in  the  food  and  drink.  A  small 
amount,  however,  is  the  result  of  the  chemical  union  of  hydrogen  with 
oxygen  in  the  blood  and  tissues.  The  total  amount  taken  into  the  body 
every  day  is  about  4J-  lbs.;  while  an  uncertain  quantity  (perhaps  ^  to 
f  lb. )  is  formed  by  chemical  action  within  it.    (Dalton. ) 

Loss. — The  loss  of  water  from  the  body  is  intimately  connected  with 
excretion  from  the  lungs,  skin,  and  kidneys,  and,  to  a  less  extent,  from 


342 


HAND-BOOK  OF  PHYSIOLOGY. 


the  alimentary  canal.  The  loss  from  these  various  organs  may  be  thus 
apportioned  (quoted  by  Dalton  from  various  observers). 

From  the  Alimentary  Canal  (faeces)      .       .  4  per  cent. 

"      Lungs   20 

Skin  (perspiration)       .       .       .  30 

Kidneys  (urine)    .       .       .       .       .       .  46 

100 

Sodium  and  Potassium  Chlorides  are  present  in  nearly  all  parts 
of  the  body.  The  former  seems  to  be  especially  necessary,  judging  from 
the  instinctive  craving  for  it  on  the  part  of  animals  in  whose  food  it  is 
deficient,  and  from  the  diseased  condition  which  is  consequent  on  its  with- 
drawal. In  the  blood,  the  quantity  of  chloride  of  sodium  is  greater  than 
that  of  all  its  other  saline  ingredients  taken  together.  In  the  muscles, 
on  the  other  hand,  the  quantity  of  chloride  of  sodium  is  less  than  that  of 
the  chloride  of  potassium. 

Calcium  Fluoride,  in  minute  amount,  is  present  in  the  bones  and 
teeth,  and  traces  have  been  found  in  the  blood  and  some  other  fluids. 

Calcium,  Potassium,  Sodium,  and  Magnesium  Phosphates 
are  found  in  nearly  every  tissue  and  fluid.  In  some  tissues — the  bones 
and  teeth — the  phosphate  of  calcium  exists  in  very  large  amount,  and  is 
the  principal  source  of  that  hardness  of  texture  on  which  the  proper  per- 
formance of  their  functions  so  much  depends.  The  phosphate  of  calcium 
is  intimately  incorporated  with  the  organic  basis  or  matrix,  but  it  can 
be  removed  by  acids  without  destroying  the  general  shape  of  the  bone; 
and,  after  the  removal  of  its  inorganic  salts,  a  bone  is  left  soft,  tough, 
and  flexible. 

Potassium  and  sodium  phosphates  with  the  carbonates,  maintain  th& 
alkalinity  of  the  blood. 

Calcium  Carbonate  occurs  in  bones  and  teeth,  but  in  much  smaller 
quantity  than  the  pliosphate.  It  is  found  also  in  some  other  parts.  The 
small  concretions  of  the  internal  ear  (otoliths)  are  composed  of  crystalline 
carbonate  of  calcium,  and  form  the  only  example  of  inorganic  crystalline 
matter  existing  as  such  in  the  body. 

Potassium  and  Sodium  Carbonates  are  found  in  tlie  blood,  and 
some  other  fluids  and  tissues. 

Potassium,  Sodium,  and  Calcium  Sulphates  are  met  with  in 
small  amount  in  most  of  the  solids  and  fluids. 

Silicon. — A  very  minute  (juantity  of  .v/Z/m  exists  in  the  urine,  and  in 
the  blood.  Traces  of  it  have  been  found  also  in  bones,  hair,  and  some  other 
parts. 

Iron. — The  especial  phice  of  iro»'  is  in  ha^uioglobin,  the  coloring- 
matter  of  the  blood,  of  which  a  further  account  has  boon  given  with  the 


APPENDIX. 


o43 


chemistry  of  the  blood.  Peroxide  of  iron  is  found,  in  very  small  quanti- 
ties, in  the  ashes  of  bones,  muscles,  and  many  tissues,  and  in  lymph  and 
chyle,  albumin  of  serum,  fibrin,  bile,  and  other  fluids;  and  a  salt  of  iron, 
probably  a  phosphate,  exists  in  the  hair,  black  pigment,  and  other  deeply 
colored  epithelial  or  horny  substances. 

Aluminium,  Manganese,  Copper,  and  Lead. — It  seems  most 
likely  that  in  the  human  body,  copper,  manganesium,  aluminium  and 
lead  are  merely  accidental  elements,  which,  being  taken  in  minute  quan- 
tities with  the  food,  and  not  excreted  at  once  with  the  faeces,  are  absorbed 
and  deposited  in  some  tissue  or  organ,  of  which,  however,  they  form  no 
necessary  part.  In  the  same  manner,  arsenic,  being  absorbed,  may  be 
deposited  in  the  liver  and  other  parts. 


APPENDIX  B, 


MEASURES  OF  WEIGHT  {Amirdupois). 


lbs. 

Kecent  Skeleton      .       .  21 
Muscles  and  Tendons      .  77 
Skin    and  Subcutaneous 
tissue    .       .       .  .16 


Blood 


Brain 


"  Cerebrum  . 
Cerebellum . 
Pons  and  Medulla 
oblongata  . 


11  to  14 
.  2 


Encephalon 

Eyes 
Heart 

Intestines,  small 
large 

Kidneys  (both) 
Larynx,  Trachea,  and  larger 
Bronchi 


12 

5i 


i 

10 

Hi 
1 

104 


es.) 


lbs. 


10 


1| 


-  3 

-  2 

-  7 


Liver  ....  3 
Lungs  (both)  .  .  .2 
(Esophagus  .  .  .  - 
Ovaries  (both)  .       .    J  to  - 

Pancreas 

Salivary  Glands  (both 
sides)    .       .       .  1^  to 

Stomach  .... 

Spinal  Cord,  divested  of  its 
nerves  and  membranes  .     -    1  i 

Spleen     .       .       .       .     -  7 

Suprarenal  Capsules  (both), 

ito  -  i 

Testicles  (both)        .   1|-  to  -  2 

Thyroid  body  and  remains 

of  Thymus  gland  .       •     -  f 

Tongue  and  Hyoid  bone  .     -  3 

Uterus  (virgin)       •    i  to     -  f 


MEASURES  OF  LENGTH  (Average). 


ft. 


6 

n 

H 

3 


Appendix  vermiformis  3  to 
Bronchus,  right 
left  . 

Caecum  .... 
Duct,  common  bile  . 

^'  ejaculatory, 
ito 

of  Cowper's  gland 
hepatic 
nasal 
"    parotid  . 
sub-maxillary 
Epididymis 

unraveled.       .  20 
Eustachian  tube 
Eallopian  tube  . 

Intestine,  large  .       .      5  to  6  - 
small  .       .       .  20  - 
Ligament,  round,  of  uterus     -  4^ 


-  2 

-  -I 

-  H 

-  2 

-  H 


Ligament  of  ovary 
Meatus  auditorius  externus 
Medulla  oblongata 
(Esophagus 
Pancreas  . 
Pharynx 
Rectum 
Spinal  cord 
Tubulus  seminiferus 
Urethra,  male  . 

"  female 
Ureter 

Vagina     .       .       .    4  to 
Vas  deferens 
Vesicula  seminalis 

"  unraveled, 
4  to 

Vocal  cord 


in. 

H 

n 

H 

10 

7 

8 

1 

5 

2 

3 
8 

n 

1 

4 

6 

2 

2 

6 

-i 

346 


HAND-BOOK  OF  PHYSIOLOGY. 


SIZES  OF  VARIOUS  HISTOLOaiCAL  ELEMENTS  AND  TISSUES. 


Average  size  infractions  of  an  inch. 


Air-cells,  ^  to 

Blood-cells  (red),  g^ig-g-  (breadth). 

"    Twoo  (thickness), 
(colorless),  2§*ro-  . 
Canaliculus  of  bone,  ywqI)  (width). 
Capillary  blood-vessels,  (^^^g) 


to 


(bone). 


3  0  0  0  0* 

1—  (length). 


.1200  . 
Cartilage -cells  (nuclei  of). 
Chyle-molecules, 

Cili^^    5  0^0  0  2  5^0  0  . 

Cones  of  retina  (at  yellow  spot), 

T2W  to  Towo  (width). 
Connective-tissue  fibrils,  -g-o-Jor 

•OToo  (width). 
Dentine- tubules,  -^^^  (width). 
Enamel-fibres,  -^^oo"  (width). 
End-bulbs,  -g-^. 
Epithelium 

columnar    (intestine),  ■g-o^o'o 
(length). 

spheroidal  (hepatic),  -f-gVo  tot- 

squamous     (peritoneum)  twfo 
(width). 

squamous  (mouth),  (width), 
(skin),  (width). 


Elastic  (yel.)  fibres,  -^^^  to  ^oVo 

(wide). 
Eat-cells,  to 
Germinal  vesicle, 

spot,  3oVo- 

Glands 

gastric,      to  ^  (length). 
"      ^  to  (width). 
Lieberkuhn^s  (small  intestines), 

.^k  to  m  (length).  ^ 
Lieberkuhn's   (small  intestine), 

(width). 
Peyer^s  (follicles),  ^  to 
Sweat,  (width). 

in  axilla,  ^  to  \  (width). 
Ilaversian    canals,   jtrVo-  to 
(width). 


Lacunae  (bone),  ygVo  (length). 

-         3^1^^  (width). 

Macula  lutea,  -g^. 

Malpighian  bodies  (kidney),  y^-g-. 

corpuscles  (spleen), 


to  3V 


"^0  0 


to 
to 


Too- 


Muscle  (striated), 

(width). 
Muscle-cell  (plain 
length). 

Muscle-cell  (plain),  ^^Vo  to  -^^-^ 
(width). 

IsTerve-corpuscles  (brain),  -^^^  to 

TTO* 

Nerve-fibres  (medullated)  jgwo  to 

TToo  (width). 
Nerve- fibres  (non-medullated)  -g-^ro 

to  50V0  (width). 
Ovum,  y^o-. 

Pacinian  bodies,  -^^  to  (length). 

".   ^  to  ^  (width). 
Papillae  of  skin  (palm),       to  yot 
(length). 
"      "  (face),  8^  to 
"      tongue  (circumvallate), 
to  tV  (width), 
(fungiform),  J,  to 
(width). 
"      "  (filiform),  yV  (length). 
Pigment-cells    of    choroid  (hexa- 
gonal), yoVir- 
Pigment-granules,  ^o^oo- 
Spermatozoon,        to  -^j^  (length), 
neau,  g-ooo 
-  y^nro- (width). 
Touch-corpuscle,  (length). 
Tubuli    seminiferi,    ^-J-g-    to  y-J-g- 

(width). 
Tubuli  uriniferi,  -gi-g-. 
Villi,      to  i  (length). 
"    ^ir  to  ^  (width). 


APPENDIX. 


347 


SPECIFIC  GRAVITY  OF  VARIOUS  FLUIDS  AND  TISSUES. 
(Water  =  I'OOO.) 


Adipose  tissue  . 

.  0 

•932 

Bile  .... 

.  1 

•020 

Blood 

.  1 

•055 

corpuscles  (red) 

.  1 

•088 

Body  (entire)  . 

.  1 

•065 

Bone        .       .  1 

•870  to  1 

•970 

Brain 

.  1 

•036 

grey  matter 

.  1 

•034 

"  white 

.  1 

•040 

Cartilage  . 

.  1 

•150 

Cerebro-spinal  fluid  . 

.  1 

•006 

Chyle.  . 

.  1 

•024 

Gastric  juice 

.  1 

•0023 

Intestinal  juice . 

.  1 

Oil 

Kidney 

.  1 

•052 

Liquor  amnii  . 

.  1 

•008 

Liver   1.055 

Lymph  ....  1^020 
Lungs 

when  fully  distended  .  0*126 
ordinary  condition,  post 

mortem       .      0*345  to  0.746 

when  deprived  of  air      .  1*056 

Muscle       ....  1-020 

Milk  .       .       .       .       .  1-030 

Pancreatic  juice  .       .       .  1  '012 

Saliva  ....  1*006 
Serum       .       .       .  .1*026 

Spleen       ....  1.060 

Sweat        ....  1*004 

Urine        ....  1*020 


TABLE  SHOWING  THE  PERCENTAGE  COMPOSITION  OF  VARIOUS 
ARTICLES  OF  FOOD.  (Letheby.) 


Water. 

Albumin. 

Starch. 

Sugar. 

Fat. 

Salts. 

Bread 

.  37 

8*1 

47*4 

3*6 

1*6 

2*3 

Oatmeal  . 

.  15 

12*6 

58*4 

5*4 

5*6 

3* 

Indian  corn  meal 

.  14 

11*1 

64*7 

0*4 

8*1 

1*7 

Rice 

.  13 

6*3 

79*1 

0*4 

0*7 

0*5 

Arrowroot 

.  18 

82* 

Potatoes  . 

.  75 

2*1 

18*8 

3*2 

0*2 

0-7 

Carrots  . 

.  83 

1*3 

8*4 

6*1 

0*2 

1-0 

Turnips  . 

.  91 

1*2 

5-1 

2*1 

0^6 

Sugar 

.  5 

95*0 

Treacle  . 

.  23 

77*0 

Milk 

.  86 

4*1 

5*2 

3*9 

0^8 

Cream 

,  66 

2*7 

2*8 

26*7 

1^8 

Cheddar  cheese 

.  36 

28*4 

31*1 

4^5 

Lean  beef 

.  72 

19*3 

3^6 

5*1 

Fat  beef  . 

.  51 

14*8 

29^8 

4*4 

Lean  mutton  .  . 

.  72 

18*3 

4^9 

4*8 

Fat  mutton 

.  53 

12*4 

31*1 

3*5 

Veal 

.  63 

16*5 

15*8 

4*7 

Fat  pork  . 

.  39 

9*8 

48*9 

2*3 

Poultry  . 

.  74 

21^0 

3*8 

1*2 

White  fish 

.  78 

18*1 

2*9 

1^0 

Eels 

.  75 

9^9 

13*8 

1-3 

Salmon  . 

.  77 

16*1 

5*5 

1-4 

White  of  egg  . 

.  78 

20*4 

1*6 

Yelk  of  egg 

.  52 

16*0 

30-7 

1*3 

Butter  and  Fat 

.  15 

83*0 

2*0 

Beer  and  porter 

.  91 

0*1 

8-7 

0-2 

348 


HAND-BOOK  OF  PHYSIOLOGY. 


CLASSIFICATION  OF  THE  ANIMAL  KINGDOM. 
Vertebrata. 

Mammalia  Typical  Examples, 

Primates     ....  Man. 

.    Ape.  baboon. 
.    Bat,  flying  fox. 
.    Mole,  hedgehog. 
.    Lion,  dog,  bear,  seal. 
.  Elephant. 
.  Hyrax 


Chiroptera 
Insectivora 
Carnivora 
Proboscidea 
Hyracoidea  . 
Ungnlata: 

Perissodactyla 

Artioclactyla 

Sirenia 
Cetacea 
Eodentia 

Edentata 

Marsupiata  . 

Monotremata 

Birds 

Caei^^'at^ 

Kaptores  {Birds  of  Prey) 
Scansores  [Climhing  Birds) 
Passeres  {Perching  Birds) 
Easores  (Scratcliing  Birds) 
Grallatores  ( Wading  Birds) 
Natatores  {Swimming  Birds) 

Eatit^ 

Cursores  {Etmning  Birds)  . 

Eeptiles 
Crocodilia 
Lacertilia 

Chelonia 
Ophidia 

Amphibia 
Anura 
Urodela 

Fish 
Dipnoi 
Teleostei 
Placoidei 
Ganoidei 
Cyclostomi 
Leptocardii 


Tapir,  rhinoceros,  horse. 

Hippopotamus,  pig,  camel,  chevrotain, 
deer,  ox,  sheep,  goat,  giraffe. 

Dugong,  manatee. 

Whale,  porpoise,  narwhal. 

Hare,  porcupine,  guinea  pig,  rat,  beaver, 
squirrel,  dormouse. 

Armadillo,  pangolin,  true  anteater, 
Cape  anteater,  sloth. 

Opossum,  bandicoot,  Thylacinus,  pha- 
langer,  wombat,  kangaroo. 

Ornithorhynchus,  or  duck-billed  platy- 
pus. Echidna  or  spiny  anteater. 


Vulture,  hawk,  owl. 
Woodpecker,  parrot. 
Crow,  finch,  swallow. 
Fowl,  pheasant,  grouse. 
Heron,  stork,  snipe,  crane. 
Penguin,  duck,  pelican,  gull. 

Ostrich,  emeu,  apteryx. 

Crocodile,  alligator. 
Iguana,  chameleon,  gecko,  lizard,  slow- 
worm,  flying  dragon. 
Tortoise,  turtle 
Snake,  viper. 

Frog,  toad. 
Newt,  salamander. 

Tjcpidosiren. 

IVrch,  mackerel,  cod,  herring. 
Sliark,  ray. 
Sturgeon,  bony  pike. 
Lamprey,  hag. 
Am])liioxus  lancoolatus. 


APPENDIX. 


349 


CLASSIFICATION  OF  THE  ANIMAL  KINGDOM. 


MOLLUSCA 
Cephalopoda 

Pteropoda  . 

Gasteropoda: 

Pulmonigasteropoda 
Branchiogasteropoda 

Lamellibranchiata 
Brachiopoda 

Tunicata,  or  Ascidioidea 

Bryozoa  or  Polyzoa 

Arthkopoda 

Insecta       .       •  • 


Arachnida  . 
Myriopoda  . 
Crustacea  . 


Invertebrata. 

Typical  Examples, 
,    Octopus,  argonaut,  squid,  cuttle-fish, 

nautilus. 
.    Clio,  Cleodora. 

.  Snail,  slug. 

.  Whelk,  limpet,  periwinkle. 

.  Oyster,  mussel,  cockle. 

.  Terebratula,  Lingula. 

.  Salpa,  Pyrosoma. 

.  Sea  mat. 


Beetle,  bee,  ant,  locust,  grasshopper, 
cockroach,  earwig,  moth,  butterfly, 
fly,  flea,  bug. 

Scorpion,  spider,  mite. 

Centipede,  millipede. 

Crab,  lobster,  crayfish,  prawn,  barnacle. 


Annulata    ....    Sea-mouse,  leech,  earthworm. 
Scolecida    ....    Hair-worm,  thread-worm,  round-worm, 

fluke,  tape- worm,  guinea-worm. 
Echinodermata   .       .       .    Sea- cucumber,    sea-urchin,  star-fish, 

sand-star,  feather-star. 

CCELEN^TERATA 

Ctenophora.       •       .       .  Beroe. 

Anthozoa    .       •      .       .    Sea  anemone,  coral,  sea-pen. 
Hydrozoa    ....    Hydra,  Sertularia,  Velella,  Portuguese 

man-of-war. 
Spongida    ....  Sponges. 

Protozoa 

Khizopoda  ....    Poraminifera,  Amoeba. 
Infusoria    ....    Paramoecium,  Vorticella. 


i 


1 


INDEX 


Abdominal  muscles,  action  of  in  respi- 
ration, i,  187 
Aberration, 

chromatic,  ii,  213 

spherical,  ii,  213 
Abomasum,  i,  240 
Absorbents.    8ee  Lymphatics. 
Absorption,  i,  291 

by  blood-vessels,  i,  305 

by  lacteal  vessels,  i,  303 

by  lymphatics,  i,  303 

conditions  for,  i,  307 

by  the  skin,  i,  345 

oxygen  by  lungs,  i,  195 

process  of  osmosis,  i,  305 

rapidity  of,  i,  306.    See  Chyle,  Lymph, 
Lymphatics,  Lacteals, 
Accessory  nerve,  ii,  149 
Accidental  elements  in  human  body,  ii, 
860 

Accommodation  of  eye,  ii,  206 
Acids,  organic,  ii,  339 

acetic,  ii,  339 
Acid-albumin,  i,  247;  ii,  846 
Acini  of  secreting  glands,  i,  323 
Actinic  rays,  ii,  224 
Addison's  disease,  ii,  10 
Adenoid  tissue,  i,  34 
Adipose  tissue,  i,  35.    See  Fat. 

development,  i,  36 

situations  of,  i,  36 

structure  of,  i,  36 
Adrenals,  ii,  8 
After-birth,  ii,  270 
After-sen  sations, 

taste,  ii,  174  • 

touch,  ii,  168 

vision,  ii,  216 
Aggregate  glands,  i,  323 
Agminate  glands,  i,  258 
Air, 

atmospheric,  composition  of,  i,  192 

breathing,  i,  189 

complemental,  i,  189 

reserve,  i,  189 

residual,  i,  189 

tidal,  i,  189 

changes  by  breathing,  i,  193 
quantity  breathtd,  i,  189 


Air,  transmission  of  sonorous  vibrations 
through,  ii,  186 
in  tympanum,  for  hearing,  ii,  188 
undulations  of,  conducted  by  external 
ear,  ii,  186 

Air-cells,  i,  180 

Air-tubes,  i,  177.    See  Bronchi. 
Alanines,  ii,  331 
Albino-rabbits,  i,  21 
Albumin,  ii,  327 
acid,  i,  247 

action  of  gastric  fluid  on,  i,  247 
alkali,  ii,  327,  328 

characters  of,  ii,  328 

chemical  composition  of,  ii,  327 

derived,  ii,  328 

egg,  ii,  328 

native,  ii,  328 

serum,  i,  85;  ii,  327 

tissues  and  secretion  in  which  it  ex- 
ists, ii,  327 

of  blood,  i,  83 
Albuminoids,  ii,  327 
Albuminose,  ii,  329 
Albuminous  substances, 

absorption  of,  i,  285 

action  of  gastric  fluid  on,  i,  247 
of  liver  on,  i,  280 
of  pancreas  on,  i,  266 
Alcoholic  drinks,  effect  on  respiratory 

changes,  i,  194 
Alimentary  canal,  i,  224 

development  of,  ii,  294 

length  in  different  animals,  i,  284 
Allantoin,  ii,  334 
Allantois,  ii,  262,  263 
Alloxan,  ii,  334 
Aluminium,  ii,  343 
Amic  acids,  ii,  331 
Amides,  ii,  330 
Ammonia, 

cyanate,  of,  identical  with  urea,  i,  359; 
ii,  333 

exhaled  from  lungs,  i,  196 

urate  of,  i,  360 
Amnion,  ii,  262 

fluid  of,  ii,  263 
Amceba,  i,  7 

Amoeboid  movements,  i,  8;  ii,  213 


352 


Amoeboid  cells,  i,  29 

colorless  corpuscles,  i,  80 

cornea-cells,  i,  29 

ovura,  ii,  253 

protoplasm,  i,  7 

Tradescantia,  1,  7 
Ampliioxus,  ii,  271 
Ampulla,  ii,  182 

Amputation,  sensations  after,  ii,  83 
Amyloids  or  Starches,  ii,  338 
action  of  pancreas  and  intestinal  glands, 
i,  267,  283 
of  saliva  on,  i,  231 
Amylopsin,  i,  267 
Anacrotic  wave,  i,  146 
Anastomoses  of  muscular  fibres  of  beart, 
i,  107 
of  nerves,  ii,  73 
of  veins,  i,  161 
in  erectile  tissues,  i,  169 
Anelectrotonus,  ii,  47 
Angle,  optical,  ii,  221 
Angulus  opticus  seu  visorius,  ii,  220 
Animal  heat,  i,  309.    See  Heat  and  Tem- 
perature, 

Animals,  distinctive  characters,  1,  3 
Antialbumate,  ii,  329 
Antialbumose,  ii,  329 
Antihelix,  ii,  179 
Antipeptone,  ii,  329 
Antitragus,  ii,  179 
Anus,  i,  224 
Aorta,  i,  128 

development,  281 

pressure  of  blood  in,  i,  151 

valves  of,  i,  110 
action  of,  i,  114 
Aphasia,  ii,  130 
Apnoea,  i,  209.    See  Asphyxia. 
Appendices  epiploicae,  i,  262 
Appendix  vermiformis,  i,  262 
Aquaeductus, 

cochleae,  ii,  183 

vestibuli,  ii,  182 
Aqueous  humor,  ii,  204 
Arches,  visceral,  ii,  273 
Area  germinativa,  ii,  256  . 

opaca,  ii,  256 

pellucida,  li,  256 

vasculosa,  ii,  262 
Areolar  tissue,  i,  31.     See  Connective 

Tissue. 
Arsenic,  ii.  343 
Arterial  tension,  i,  148 
Arteries,  i,  128 

circulation  in,  i,  138 
velocity  of,  i,  164 

distribution,  i,  128 

muscular  contraction  of,  i,  141 

effect  of  cold  on,  i,  142 
of  division,  i,  142 

clastieily,  i,  138 
l)urp()S('s  of,  i,  138 

muscularity,  1,  130 

governed  by  nervous  system,  i,  153 


Arteries,  purposes  of,  i,  141 
nerves  of,  i,  132 

nervous  system,  influence  of,  i,  152 
office  of,  i,  153 
pressure  of  blood  in,  i,  148 
pulse,  i,  142.    See  Pulse, 
rhythmic  contraction,  i,  140 
structure,  i,  129 
distinctions  in  large  and  small  arte- 
ries, i,  130 
systemic,  i,  102 
tone  of,  i,  153 
umbilical,  793 
velocity  of  blood  in,  i,  264 
Articulate  sounds,  classification  of,  ii,  60. 

See  Vowels  and  Consonants. 
Arytenoid  cartilages,  ii,  52 

effect  of  approximation,  ii,  55 
movements  of,  ii,  54 
muscle,  ii,  52 
Asphyxia,  i,  209 
causes  of  death  in,  i,  210 
experiments  on,  i,  211 
Astigmatism,  ii,  212 
Atmospheric  air,  i,  192.    See  Air. 
pressure  in  relation  to  respiration,  i, 
193 

Auditory  canal,  ii,  179 

function,  ii,  186 
Auditory  nerve,  ii,  185 

distribution,  ii,  185 

effects  of  irritation  of,  ii,  193 
Auricle  of  ear,  ii,  179 
Auricles  of  heart,  i,  104, 106 

action,  i,  111 

capacity,  i,  107 

development,  ii.  279 

dilatation,  i,  123 

force  of  contraction,  i,  128 
Automatic  action,  ii,  88 

cerebrum,  ii,  127 

medulla  oblongata,  ii,  110 

respiratory,  ii,  110 
Axis-cylinder  of  nerve-fibre,  ii,  70 


B. 

Barytone  voice,  ii,  57 
Basement-membrane, 

of  mucous  membranes,  i,  322 

of  secreting  membranes,  i,  319 
Bass  voice,  ii,  57 
Jiattery,  Daniell's,  ii,  26 
Benzoic  acid,  i,  372 
Bi('usi)id  valve,  i,  109 
Bile,  i,  273 

antiseptic  power,  i,  279 

coloring  matter,  i,  274 

coni])osition  of,  i,  273 

digestive  properties,  i,  279 

cxcrementitious.  i,  277 

fat  made  capable  of  absorption  by,  i, 
279 


INDEX. 


353 


Bile,  functions  in  digestion,  i,  279 
mixture  with  chyme,  i,  279 
mucus  in,  i,  275 
natural  purgative,  i,  279 
process  of  secretion  of,  i,  276 
quantity,  i,  277 
re-absorption,  i,  276,  280 
salts,  i,  273 

secretion  and  flow,  i,  276 

secretion  in  foetus,  i,  277 

tests  for,  i,  274,  275 

uses,  i,  277 
Bilifulvin,  Biliprasin,  Bilirubin,  Biliver- 

din,  i,  274 
Bilin,  i,  273 

preparation  of,  i,  273 

re-absorption  of,  i,  265,  280 
Bioplasm,  i,  6.   See  Protoplasm. 
Birth,  i,  1 

Bladder,  urinary,  i,  349.     See  Urinary 

Bladder. 
Blastema,  i,  5,    See  Protoplasm. 
Blastodermic  membrane,  ii,  254 
Bleeding,  effects  of,  on  blood,  i,  87 
Blind  spot,  ii,  215 
Blood,  i,  63 
albumin,  i,  85 
use  of,  i,  99 
arterial  and  venous,  i,  87 
assimilation,  i,  99 
buffy  coat,  i,  66 
chemical  composition,  i,  83 
coagulation,  i,  65 
color,  i,  63,  87 

changed  by  respiration,  i,  198 
coloring  matter,  i,  83,  90 
coloring  matter,  relation  to  that  of 

bile,  i,  275 
composition,  chemical,  i,  82 

variations  in,  i,  87 
corpuscles  or  cells  of,  i,  74.  See  Blood 
corpuscles, 
red,  i,  75 
white,  i,  79 
crystals,  i,  91 
cupped  clot,  i,  66 
development,  i,  96 
extractive  matters,  i,  86 
fatty  matters,  i,  86 

use  of,  i.  99 
fibrin,  i,  65,  84 
separation  of,  1,  66 
use  of,  i,  99 
formation  in  liver,  i,  82 

in  spleen,  ii,  4 
gases  of,  i,  88 

hsemoglobin  or  cruorin,  i,  83,  91 
hepatic,  i,  87 
menstrual,  ii,  242 
odor  or  halitus  of,  i,  63 
portal,  characters  of,  i,  87 

purification  of,  by  liver,  i,  277 
quantity,  i,  63 
reaction,  i,  63 

relation  of,  to  lymph,  i,  302 
Vol.  II.— 20. 


Blood,  saline  constituents,  i,  86 
uses  of,  i,  99 
serum  of,  i,  85 
compared  with  secretion  of  serous 
membrane,  i,  320 
specific  gravity,  i,  63 
splenic,  i,  88 

structural  composition,  i,  75 

temperature,  i,  63 

uses,  i,  99 
of  various  constituents,  i,  99 

variations   of,  in    different  circimi- 
stances,  i,  86 
in  different  parts  of  body,  1,  87 
Blood-corpuscles,  red,  i,  75 

action  of  reagents  on,  i,  75 

chemical  composition,  i,  83 

development,  i,  96,  97 

disintegration  and  removal,  i,  99 

method  of  counting,  i,  81 

rouleaux,  i,  76 

sinking  of,  i,  66 

specific  gravity,  i,  75 

stroma,  i,  75 

tendency  to  adhere,  i,  75 

uses,  1,  100 

varieties,  i,  75 

vertebrate,  various,  i,  76 
Blood-corpuscles,  white,  i,  79 

amoeboid  movements  of,  i,  80 

derivation  of,  i,  99 

formation  of,  in  spleen,  i,  99;  ii,  4 

locomotion,  i,  80 
Blood-crystals,  i,  91 
Blood-pressure,  i,  148 

influence  of  vaso-motor  system  of,  i, 
155 

variations,  i,  152 
Blood-vessels, 
absorption  by,  i,  305 
circumstances  influencing,  i,  307 
difference  from  lymphatic  absorp- 
tion, i,  305 
osmotic  character  of,  i,  306 
rapidity  of,  i,  306 
development,  ii,  277 
influence  of  nervous  system  on,  i,  153 
relation  to  secretion,  i,  326 
Bone,  i,  42 
canaliculi,  i,  44 
cancellous,  i,  42 
chemical  composition,  i,  42 
compact,  i,  42 
development,  i,  46 
functions,  i,  55 
Haversian  canals,  i,  45 
lacunae,  i,  44 
lamellae,  i,  46 
medullary  canal,  i,  43 
periosteum,  i,  43 
structure,  i,  42 
growth,  i,  54 
Brain.  See  Cerebellum,  Cerebrum,  Pons, 
etc. 
adult,  ii,  126 


354 


INDEX. 


Brain,  amphibia,  ii.  125 
apes,  ii,  126 
birds,  ii,  126 
capillaries  of,  i,  135,  167 
child,  ii,  126 

circulation  of  blood  in,  i,  167 

convolutions,  ii,  120 

development,  ii,  288 

female,  ii,  126 

fish,  ii,  125 

gorilla,  ii,  126 

idiots,  ii,  126 

lobes,  ii,  122 

male,  ii,  126 

mammalia,  ii,  126 

orang,  ii,  127 

proportion  of  water  in,  ii,  341 

quantity  of  blood  in,  i,  167,  et  seq. 

rabbit,  ii,  126 

reptiles,  ii,  126 

weight,  ii,  126 
relative,  ii,  126 
Breathing,  i,  172.    See  Respiration. 
Breathing-air,  i,  189 

Bronchi,  arrangement  and  structure  of, 
i,  177 

Bronchial  arteries  and  veins,  i,  182 
Brownian  movement,  i,  7 
Brunner's  glands,  i,  257 
Buffy  coat,  formation  of,  i,  66 
Bulbus  arteriosus,. ii,  281 
Burdach's  column,  ii,  96 
Bursse  mucosae,  1,  320 


C. 

Caecum,  i,  261 

Calcification,  compared  with  ossification, 

i,  51 
Calcium,  ii,  342 

fluoride,  ii,  342 
phosphate,  ii,  342  ^ 
carbonate,  ii,  342  ^ 
Calculi,  biliary,  containing  cholesterin, 

ii,  338 

containing^ copper,  i,  276 
Calyces  of  the  kidney,  i,  347 
Canal,  alimentary,  i,  224.    See  Stomach, 
Intestine,  etc. 

external  auditory,  ii,  179 
function  of,  ii,  186 

spiral,  of  cochlea,  ii,  185 
Canaliculi  of  bone,  i,  44 
Canalis  membranaceus,  ii,  185 
Canals,  Haversian,  i,  45 

portal,  i,  269 

semicircular,  ii,  182 

function  of,  ii,  191 
Cancellous  texture  of  bone,  1,  42 
Capacity  of  chest,  vital,  i,  189 

of  heart,  i,  107 
C'apill^u•i(^H,  i,  l'J^2 

circulation  in,  i,  158 
rate  of,  i,  165 


Capillaries,  contraction  of,  i,  161 
development,  ii,  277 
diameter  of,  i,  133 
influence  of  on  circulation,  i,  161 
lymphatic,  i,  292 
network  of,  i,  134 
number,  i,  135 

passage  of  corpuscles  through  walls  of, 
i,  159 

resistance  to  flow  of  blood  in,  i,  158 

still  layer  in,  i,  158 

structure  of,  i,  133 

of  lungs,  i,  134 

of  stomach,  i,  244 
Capric  acid,  ii,  339 
Caproic  acid,  ii,  339 
Capsule  of  Glisson,  i,  268 
Capsules,  Malpighian,  i,  348,  352, 
Carbonic  acid  in  atmosphere,  i,  192 

in  blood,  i,  88 

effect  of,  i,  204 

exhaled  from  skin,  i,  345 

increase  of  in  breathed  air,  i,  193 

in  lungs,  i,  197 

in  relation  to  heat  of  body,  i,  311 
Carbonates,  ii,  342 

Cardiac  orifice  of  stomach,  action  of,  i, 
250 

sphincter  of,  i,  251 
relaxation  in  vomiting,  i,  251 
Cardiac  revolution,  i,  117 
Cardiograph,  i,  119 
Carnivorous  animals,  food  of,  i,  221 

sense  of  smell  in,  ii,  178 
Cartilage,  i,  38 

articular,  i,  38 

cellular,  i,  40 

chondrin  obtained  from,  ii,  330 
classification,  i,  38 
development,  i,  42 
elastic,  i,  40 

fibrous,  i,  41,    See  Fibro-cartilage. 

hyaline,  i,  38 

matrix,  i.  39 

ossification,  i,  51 

perichondrium  of,  i,  52 

structure,  i,  38 

temporary,  i,  40 

uses,  i,  42 

varieties,  i,  38 
Cartilage  of  external  ear,  used  in  hear- 
ing, ii,  186 
Cartilages  of  larynx,  ii,  52 
Casein,^ii,  327,  328.    See  Milk. 
Cauda  equina,  ii,  90 
Caudate  ganglion  corpuscles,  ii,  78 
Cause  of  "fluidity  of  livinir  blood,  ii,  72 
Cells,  i,  9    ^  ' 

abrasion,  i,  14 

auKvboid.  i,  29 

blood,  i,  74.    See  Blood-corpuscles, 
cartilage,  i,  38 

chemical  transformation,  i,  14 
ciliated,  i.  25 
classification,  i.  16 


INDEX. 


355 


Cells,  contents  of,  i,  9 
decay  and  death,  i,  14 
definition  of,  i,  9 

epithelium,  i,  19.  See  Epithelium. 

fission,  i,  12 

formative,  ii,  255 

functions,  i,  14 

gemmation,  i,  11 

gustatory,  ii,  173 

lacunar  of  bone,  i,  44 

modes  of  connection,  i,  16 

nutrition,  i,  9 

action  of,  in  secretion,  i,  235 
olfactory,  ii,  176 
pigment,  i,  21 
reproduction,  i,  11 
segmentation,  i,  12 
structure  of,  i,  9^ 
transformation,  i,  14 
varieties,  i,  15,  16 
vegetable,  i,  7 
distinctions  from  animal  cells,  i,  3 
Cellular  cartilage,  i,  40 
Cement  of  teeth,  i,  58 
Centres,  nervous,  i,  154,  155,  etc.  See 
Kerve-centres, 
of  ossification,  i,  54 
Centrifugal  nerve- fibres,  ii,  80 
Centripetal  nerve-fibres,  ii,  80 
Cerebellum,  ii,  115 
co-ordinating  function  of,  ii,  118 
cross-action  of,  ii,  119 
effects  of  injury  of  crura,  ii,  119 

of  removal  of,  ii,  118 
functions  of,  ii,  118 
in  relation  to  sensation,  ii,  118 
to  motion,  ii,  118 
to  muscular  sense,  ii,  119 
to  sexual  passion,  ii,  119 
structure  of,  ii,  116 
Cerebral  circulation,  i,  167 

hemispheres,  ii,  120.    See  Cerebrum. 
Cerebral  nerves,  ii,  136 
third,  ii,  137 
effects  of  irritation  and  injury  of,  ii, 
137 

relation  of  to  iris,  ii,  137 
fourth,  ii,  138 
fifth,  ii,  139 

distribution  of,  ii,  139 
effect  of  division  of,  ii,  139 
influence  of  on  iris,  ii,  141 

on  muscles  of  mastication,  ii,  139 

on  organs  of  special  sense,  ii,  141, 
et  seq. 

relation  of,  to  nutrition,  ii,  142 
resemblance  to  spinal  nerves,  ii,  139 
sensory  function  of  greater  division  of 

fifth,  ii,  139 
sixth,  ii,  143 
communication    of,   with  sympa- 
thetic, ii,  144 
seventh,  ii,  144.    See  Auditory  Nerve 

and  Facial  Nerve, 
eighth,  ii,   145,  et  seq.    See  Glosso- 


pharyngeal, Pneumogastric,  and 
Spinal  Accessory  Nerves, 
ninth,  ii,  150 

Cerebration,  unconscious,  ii,  130 

Cerebrin,  ii,  332 

Cerebro- spinal  fluid,  relation  to  circula- 
tion, i,  168 
Cerebro-spinal  nervous  system,  ii,  88,  et 

seq.    See  Brain,  Spinal  Cord,  etc. 
Cerebrum,  its  structure,  ii,  120,  123 

chemical  composition,  ii,  125 

convolutions  of,  ii,  120,  et  seq, 

crura  of,  ii,  113. 

development,  ii,  288 

distinctive  character  in  man,  ii,  126 

effects  of  injury,  ii,  128 

electrical  stimulation,  ii,  131 

functions  of,  ii,  127 

grey  matter,  ii,  123 

in  relation  to  speech,  ii,  131 

localization  of  functions,  ii,  129 

structure,  ii,  123,  et  seq. 

unilateral  action  of,  ii,  129 

white  matter,  ii,  125 
Cerumen,  or  ear-wax,  i,  339 
Chalk-stones,  i,  360 

Characteristics  of  organic  compound,  326 
Charcoal,  absorption  of,  i,  307 
Chemical  composition  of  the  human 

body,  ii,  326-343 
Chest,  its  capacity,  i,  189 

contraction  of  in  expiration,  i,  259 

enlargement  of  in  inspiration,  i,  183 
Chest-notes,  ii,  58 
Cheyne-Stokes'  breathing,  i,  209 
Chlorine,  ii,  342 

in  human  body,  ii,  342 

in  urine,  i,  364 
ChoTesterin,  ii,  338 

in  bile,  i,  275 
Chondrin,  ii,  804 
Chorda  dorsalis,  ii,  258 
Chorda  tympani,  i,  232,  et  seq, 
Chordae  tendinese,  i,  110 

action  of,  i,  113 
Chorion,  ii,  264 

villi  of,  ii,  265 
Choroid  coat  of  eye,  ii,  199 

blood-vessels,  ii,  203 
Choroidal  fissure,  ii,  292 
Chromatic  aberration,  ii,  213 
Chyle,  i,  301 

absorption  of,  i,  303 

analysis  of,  i,  802 

coagulation  of,  i,  302 

compared  with  lymph,  i,  301 

corpuscles  of,  i,  301.     See  Chyle-cor- 
puscles. 

course  of,  i,  291 

fibrin  of,  i,  302 

forces  propelling,  i,  303 

molecular  base  of,  i,  301 

quantity  found,  i,  302 

relation  of,  to  blood,  i,  302 
Chyle-corpuscles,  i,  301 


35G 


INDEX. 


Chyme,  i,  247 

absorption  of  digested  parts  of^  1,  285 

changes  of  in  intestines,  i,  285,  et  seq. 
aim,  i,  25;  ii,  12 
Cihary  epitheUum,  1,  25 

of  air-passages,  i,  177 

function  of,  i,  26 
Ciliary  motion,  i,  26;  ii,  12 

nature  of,  ii,  13 
Ciliary-muscles,  ii,  206 

action  of  in  adaptation  to  distances,  ii, 
209 

Ciliary  processes,  ii,  199 
Circulation  of  blood,  i,  101 

action  of  heart,  i,  111 

agents  concerned  in,  1,  170 

arteries,  i,  138 

brain,  i,  167 

capillaries,  1,  158 

course  of,  i,  100,  et  seq. 

discovery,  i,  170 

erectile  structures,  i,  168 

foetal,  ii,  286 

forces  acting  in,  i,  103 

influence  of  respiration  on,  1,  205 

peculiarities  of,  in  different  parts,  i, 
167 

portal,  i,  269 

proofs,  i,  170 

pulmonary,  i,  198 

systemic,  i,  102 

in  veins,  i,  161 
velocity  of,  i,  163 
Circumvallate  papillae,  ii,  169 
Claviculi  of  Gagliardi,  i,  46 
Cleft,  ocular,  ii,  292 
Clefts,  visceral,  ii,  273 
Clitoris,  ii,  239 

development  of,  ii,  305 
Cloaca,  ii,  303 

Clot  or  coagulum  of  blood,  i,  65.  See 
Coagulation, 
of  chyle,  i,  301 
Coagulation  of  blood,  i,  65 
absent  or  retarded,  i,  71 
conditions  affecting,  i,  71 
influence  of  respiration  on,  i,  198 
theories  of,  i,  70 
of  chyle,  i,^  301 
of  lymph,  i,  302 
Coat,  buffy,  i,  66  ^ 
Coats  of  arteries,  i,  81 
Cochlea  of  the  ear,  i,  179 

office  of,  i,  188 
Cold-blooded  animals,  i,  311 
extent  of  reflex  movements  in,  ii,  100 
retention  of  muscular  irritability  in,  ii, 
37 

Colloids,  i,  306 
Colon,  i,  261 
Colostrum,  i,  331 
Color-blin(lness,  ii,  226 
Coloring  matt(!r,  i,  274 

of  bile,  i,  274 

of  blood,  i,  83,  90 


Coloring  matter  of  urine,  i,  362 

Colors,  optical  phenomena  of,  ii,  223, 

et  seq. 
Columnae  carneae,  105 

action  of,  i,  110 
Columnar  epithelium,  i,  24 
Complemental  air,  i,  189 

colors,  ii,  225 
Compounds,  ii,  325 

inorganic,  ii,  340 

organic,  ii,  325 
Concha,  ii,  179 

use  of,  ii,  186 
Cones  of  retina,  ii,  201 
Coni  vasculosi,  ii,  247 
Conjunctiva,  ii,  196 
Connective  tissues,  i,  28 

corpuscles  of,  i,  28 

fibrous,  i,  31 

gelatinous,  i,  33 

retiform,  i,  34 

varieties,  i,  32 
Consonants,  i,  61 

varieties  of,  i,  61 
Contralto  voice,  ii,  57 
Convolutions,  cerebral,  ii,  120,  et  seq. 
Co-ordination  of  movements,  office  of 
cerebellum  in,  ii,  118 

office  of  sympathetic  ganglia  in,  ii,  155 
Copper,  an  accidental  element  in  the 
body,  ii,  343 

in  bile,  i,  276. 
Cord,  spinal,  ii,  90.    See  Spinal  Cord. 

umbilical,  ii,  270 
Cords,  tendinous,  in  heart,  i,  110 

vocal,  ii,  52.    See  Vocal  Cords. 
Corium,  i,  335 
Cornea,  ii,  197 

action  of  on  rays  of  light,  ii,  204 

corpuscles,  ii,  198 

nerves,  ii,  198 

structure,  ii,  197 

after  injury  of  fifth  nerve,  ii,  143 
Corpora  Arantii,  i,  111 
geniculata,  ii,  114 
quadrigemina,  ii,  114 

their  function,  ii,  114 
striata,  ii,  114 

their  function,  ii,  115 
Corpus  callosum,  office  of,  ii,  134 
cavernosum  penis,  i,  168 
dentatum 
of  cerebellum,  ii,  116 
of  olivary  body,  ii,  109 
luteum,  ii,  243 
of  lumian  female,  ii,  243 
of  mammalian  animals,  ii,  243 
of  menstruation  and  pregnancy  com- 
pared, ii,  245 
spongiosum  lUTthrai,  i,  169 
Corpuscles  of  blood,  i,  74.    See  Blood- 
corpuscles, 
of  chyle,  i,  301 
of  connective  tissue,  i,  28 
of  cornea,  ii,  198  • 


INDEX. 


357 


Corpuscles  of  lymph,  i,  301 

Pacinian,  ii,  74 
Correlation  of  life  with  other  forces,  ii, 
305 

Cortical  substance  of  kidney,  i,  347 

of  lymphatic  glands,  i,  298 
Corti's  rods,  ii,  184 

otfice  of,  ii,  192 
Costal  types  of  respiration,  i,  187 
Coughing,  influence  ou  circulation  in 
veins,  i,  207 

mechanism  of,  i,  200 

sensation  in  larynx  before,  ii,  84 
Cowper's  glands,  ii,  246 

office  uncertain,  ii,  251 
Cranial  nerves,  ii,  136.     See  Cerebral 
nerves. 

Cranium,  development  of,  ii,  288 
Crassamentum,  i,  65 

Crescents  of  Gianuzzi,  i,  228.    See  Semi- 

lunes  of  Heidenhain. 
Crico-arytenoid  muscles,  ii,  52 
Cricoid  cartilages,  ii,  52 
Crossed  pyramidal  tract,  ii,  95 
Crura  cerebelli, 

effect  of  dividing,  ii,  118,  et  seq. 
of  irritating,  ii,  118 

cerebri,  ii,  113 
their  office,  ii,  113 
Crusta  petrosa,  i,  58 
Cryptogamic  plants,  movements  of  spores 

of,  i,  4 
Crystal  growth  of,  i,  1 
Crystallin,  ii,  328 
Crystalline  lens,  ii,  204 

in  relation  to  vision  at  different  dis- 
tances, ii,  207 
Crystalloids,  i,  306 

blood,  i,  91 
Cubic  feet  of  air  for  rooms,  i,  205 
Cupped  appearance  of  blood-clot,  i,  66 
Curdling  ferments,  i,  248 
Currents  of  action,  ii,  36 

ascending,  ii,  46 

continuous,  ii,  26 

descending,  ii,  46 

induced,  ii,  27 

muscle,  ii,  23 

natural,  ii,  24 

negative  variation,  ii,  36 

nerve,  ii,  45 

polarizing,  ii,  47 

rest,  ii,  24,  45 
Curves,  Traube-Hering's,  i,  209 
Cuticle,  i,  333.    See  Epidermis,  Epithe- 
lium of  hair,  i,  340 
Cutis  anserina,  ii,  14 

vera,  i,  335 
Cyanate  of  ammonium,  i,  359 
Cylindrical  or  columnar  epithelium,  i,  24 
Cystic  duct,  i,  268 
Cystin  in  urine,  i,  365 

D. 

Daltonism,  ii,  226 


Daniell's  battery,  ii,  26 
Decidua, 

menstrualis,  ii,  242 

reflexa,  ii,  268 

serotina,  ii,  268 

vera,  ii,  268 
Decline,  i,  2 

Decomposition,  tendency  of  animal  com- 
pounds to,  ii,  326 
Decomposition-products,  ii,  330 
Decussation  of  fibres  in  medulla  oblon- 
gata, ii,  107 
in  spinal  cord,  ii,  99 
of  optic  nerves,  ii,  231 
Defaecation,  mechanism  of,  i,  288 

influence  of  spinal  cord  on,  ii,  102 
Deglutition,  i,  236.    See  Swallowing. 
Dentine,  i,  55 
Depressor  nerve,  i,  154 
Derived  albumins,  ii,  328 
Derma,  i,  335 

Descendens  noni  nerve,  ii,  150 
Descemet's  membrane,  ii,  198 
Development,  i,  3;  ii,  252 
of  organs,  ii,  270 

alimentary  canal,  ii,  294 

arteries,  ii,  281 

blood,  i,  96,  et  seq. 

blood-vessels,  ii,  277 

bone,  i,  46 

brain,  ii,  288 

capillaries,  ii,  277 

cranium,  ii,  288 

ear,  ii,  294 

embryo,  ii,  260 

extremities,  ii,  275 

eye,  ii,  291 

face  and  visceral  arches,  ii,  273 

heart,  ii,  276 

liver,  ii,  297 

lungs,  ii,  297 

medulla  oblongata,  ii,  290 

muscle,  ii,  20 

nerves,  ii,  287 

nervous  system,  ii,  287 

nose,  ii,  295 

organs  of  sense,  ii,  291 

pancreas,  ii,  297  • 

pituitary  body,  ii,  272 

respiratory  apparatus,  ii,  298 

salivary  glands,  ii,  296 

spinal  cord,  ii,  287 

teeth,  i,  58 

vascular  system,  ii,  276 
veins,  ii,  283 

vertebral  column  and  cranium,  ii,  270 
visceral  arches  and  clefts,  ii,  273 
of  "Wolffian  bodies,  urinary  apparatus 
and  sexual  organs,  ii,  298 

Dextrin,  i,  231 

Diabetes,  i,  283 

Diamides,  ii,  331 

Diapedesis  of  blood-corpuscles,  i,  159 
Diaphragm, 
action  of,  on  abdominal  viscera,  i,  175 


358 


mDEX. 


Diaphragm  in  inspiration,  i,  183 
in  various  respiratory  acts,  i,  198 
in  vomiting,  i,  251  • 

Diaphysis,  i,  54 

Diastole  of  heart,  i,  111 

Dicrotous  pulse,  i,  146 

Diet- 
daily,  i,  221 

influence  on  blood,  i,  87 

mixed,  necessity  of,  i,  213,  et  seq. 
Diffusion  of  gases  in  respiration,  i,  197 
Digestion,  i,  224 

in  the  intestines,  i,  284,  286 

in  the  stomach,  i,  247 

influence  of  nervous  system  on,  i,  290 

of  stomach  after  death,  i,  253.  See 
Gastric  fluid.  Food,  Stomach. 
Diplopia,  ii,  229 
Direct  cerebellar  tract,  ii,  96 

pyramidal  tract,  ii,  95 
Direction  of  sounds,  perception  of,  ii, 
194. 

Discus  proligerus,  ii,  236 
Disdiaclasts,  ii,  16 

Distance,  adaptation  of  eye  to,  ii,  207 
of  sounds,  how  judged  of,  ii,  194 

Distinctness  of  vision,  how  secured,  ii, 
203,  et  seq. 

Dormant  vitality,  ii,  308 

Dorsal  lamina?,  ii,  256,  273 

Double  hearing,  ii,  195 
vision,  ii,  229 

Dreams,  ii,  136 

Drowning,  cause  of  death  in,  i,  211 
Duct,  cystic,  i,  268 

hepatic,  i,  271 

thoracic,  i,  291 

vitelline,  ii,  261 
Ductless  glands,  ii,  1 
Ducts  of  Cuvier,  ii,  285 
Ductus  arteriosus,  ii,  282 

venosus,  ii,  284,  286 

closure  of,  ii,  286 
Duodenum,  i,  254 

Duration  of  impressions  on  retina,  ii,  216 

Duverney's  glands,  ii,  283 

Dysphagia,  absorption  from  nutritive 

baths  in,  i,  346 
Dyspnoea,  i,  209 


E. 

Ear,  ii,  179 
bones  or  ossicles  of,  ii,  180 

function  of,  ii,  188 
development  of,  ii,  294 
external,  ii,  179 
function  of,  ii,  186 
internal,  ii,  181 

function  of,  ii,  191 
middle,  ii,  180 

function  of,  ii,  187 
Ectopia  vcsicjv,  i,  372  ^ 
Efferent  ncrve-libres,  ii,  80 


Efferent  lymphatics,  i,  300 

vessels  of  kidney,  i,  352 
Egg-albumin,  ii,  327 
Eighth  cranial  nerve,  ii,  145 
Elastic  cartilage,  i,  40 

fibres,  i,  30 

tissue,  i,  33 
Elastin,  ii,  330 
Electricity, 

in  muscle,  ii,  21 
nerve,  ii,  45 
retina,  ii,  218 
Electrodes,  ii,  22 
Electrotonus,  ii,  47 

Elementary  substances  in  the  human 
body,  ii,  325 

accidental,  ii,  343 
Embryo,  ii,  255.    See  Development  and 
Foetus,  formation  of  blood  in,  i,  96 
Emmetropic  eye,  ii,  211 
Emotions,  connection  of  with  cerebral 

hemispheres,  ii,  127 
Enamel  of  teeth,  i,  57 
Enamel  organ,  i,  58 
End-bulbs,  i,  337 
End- plates,  motorial,  ii,  76 
Endocardium,  i,  108 
Endolymph,  ii,  182 

function  of,  ii,  191 
Endomysium,  ii,  15 
Endoneurium,  ii,  69 
Endosmometer,  i,  305 
Endothelium,  i,  21 

distinctive  characters,  i,  21 

germinating,  i,  23 
Energy,  ii,  65 

relations  of  vital  to  physical,  chap.  xx. 

daily  amount  expended  in  body,  ii,  65 
Epencephalon,  ii,  290 
Epiblast,  ii,  255 
Epidermis,  i,  333 

development,  etc.,  of,  i,  334 

functions  of,  i,  342 

hinders  absorption,  i,  335 

pigment  of,  i,  334 

relation  to  sensibility,  i,  342 

structure  of,  i,  333 

thickening  of,  i,  334 
Epididymis,  ii,  247 
Epiglottis,  ii,  52 

action  in  swallowing,  i,  238 

influence  of  on  voice,  ii,  55 
Epincurium,  ii,  69 
Epiphysis,  i,  54 
Epithelium,  i,  19 

air-cells,  i,  182 

arteries,  i,  130  * 

bronchi,  i,  177 

bronchial  tubes,  i,  177 

ciliated,  i,  25 

cogged,  i,  21 

columnar,  i.  24 

cylindrical,  i,  24 

development,  i,  27 

glandular,  i,  24 


INDEX. 


Epithelium,  goblet-sliaped,  i,  25 
o^rowth,  i,  28 

mucous  membranes,  i,  322 
olfactory  region,  ii,  176 
secreting  glands,  i,  323 
serous  membranes,  i,  319 
spheroidal,  i,  23 
squamous  or  tessellated,  i,  20 
transitional,  i,  26 
Erect  position  of  objects,  perception  of, 
ii,  219 

Erectile  structures,  circulation  in,  i,  168 
Erection,  i,  168 
cause  of,  i,  168 

influence  of  muscular  tissue  in,  i,  169 

a  reflex  act,  ii,  103 
Erythro-granulose,  ii,  105 
Erythro-dextrin,  ii,  336 
Eunuchs,  voice  of,  ii,  58 
Eustachian  tube,  ii,  180 

development,  ii,  294 

function  of,  ii,  190 
Eustachian  valve,  i,  105 
Excito-motor  and  sensori-motor  acts,  ii, 
85 

Excreta  in  relation  to  muscular  action, 

ii,  44,  et  seq. 
Excretin,  i,  287 
Excretion,  i,  347 
Excretoleic  acid,  i,  287 
Exercise, 

effects  of,  on  production  of  carbonic 
acid,  i,  194 
on  temperature  of  body,  i,  310 
on  venous  circulation,  i,  162 
Expenditure  of  body,  ii,  63 
amount,  ii,  63 

compared  with  income,  ii,  64 

evidences,  ii,  63 

objects,  ii,  65 

sources,  ii,  65 
Expiration,  i,  186 

influence  of,  on  circulation,  1,  207 

mechanism  of,  i,  186 

muscles  concerned  in,  i,  187 

relative  duration  of,  i,  188 
Expired  air,  properties  of,  i,  193,  et  seq. 
Extractive  matters,  i,  193 

in  blood,  i,  86 

in  urine,  i,  363 
Extremities,  development  of,  ii,  275 
Eye,  ii,  196 

adaptation  of  vision  at  different  dis- 
tances, ii,  203,  et  seq. 

blood-vessels,  ii,  203 

capillary  vessels  of,  ii,  199 

development  of,  ii,  291 

effect  on,  of  injury  of  facial  nerve,  ii, 
144 

of  fifth  nerve,  ii,  141,  143 
fcffect  of  pressure  on,  ii,  229 
lerves,  supplying  muscles  of,  ii,  137, 

138,  143 
Dptical  apparatus  of,  ii,  302 
refracting  media  of,  ii,  204 


Eye,  resemblance  to  camera,  ii,  214 

structure  of,  ii,  197 
Eyelids,  i,  196 

development  of,  ii,  293 
Eyes,  simultaneous  action  of  in  vision,  ii, 
228 


F. 

Face,  development  of,  ii,  273 
effect  of  injury  of  seventh  nerve  on,  ii, 
144 

Facial  nerve,  ii,  144 

effects  of  paralysis  of,  ii,  144 

relation  of,  to  expression,  ii,  144 
Faeces,  composition  of,  i,  287 

quantity  of,  i,  287 
Fallopian  tubes,  ii,  238 

opening  into  abdomen,  ii,  238 
Falsetto  notes,  ii,  59 
Fasciculus, 

cuneatus,  ii,  96 

olivary,  ii,  96 

teres,  ii,  96 
Fasting, 

influence  on  secretion  of  bile,  i,  276 
Fat.    See  Adipose  tissue. 

action  of  bile  on,  i,  279 
of  pancreatic  secretion  on,  i,  267 
of  small  intestine  on,  i,  284 

absorbed  by  lacieals,  i,  303 

formation  of,  ii,  66 

in  blood,  i,  86 

in  relation  to  heat  of  body,  i,  315 

of  bile,  i,  275 

of  chyle,  i,  301 

situations  where  found,  i,  35 

uses  of,  i,  37 
Fechner's  law,  ii,  217 
Female  generative  organs,  ii,  234 
Fenestra  ovalis,  ii,  182 

rotunda,  ii,  183 
Ferments,  i,  69,  231,  246,  266,  267. 
Fibres,  i,  17 

of  Muller,  ii,  203 
Fibrils  or  filaments,  i,  17 
Fibrin,  ii,  329,  in  blood,  i,  65 

use  of,  i,  99 

in  chyle,  i,  302 

formation  of,  i,  65 

in  lymph,  i,  302 

sources  and  properties  of,  ii,  329 

vegetable,  i,  216 
Fibrinogen,  i,  68,  et  seq. 
Fibrinoplastin,  i,  68 
Fibro-cartilage,  i,  49 

classification,  i,  41 

development,  i,  41 

uses,  i,  41 

white,  i,  41 

yellow,  i,  40 
Fibrous  tissue,  i,  31 

white,  i,  31 

yellow,  i,  32 


360 


INDEX. 


Fibrous  development,  i,  34 
Field  of  vision,  actual  and  ideal  size  of, 
ii,  320 

Fifth  nerve,  ii,  139.  8ee  Cerebral  Nerves. 

Fillet,  ii,  106 

Filtration,  i,  325 

Filum  terminale,  ii,  90 

Fimbriae  of  Fallopian  tube,  ii,  238 

Fingers,  development  of,  ii,  275 

Fish, 

temperature  of,  i,  311 
Fissures, 
of  brain,  ii,  120,  et  seq. 
of  spinal  cord,  ii,  90 
Fistula,  gastric,  experiments  in  cases  of, 

i,  245,  246 
Flesh,  of  animals,  i,  214 
Fluids,  passage  of,  through  membranes, 
i,  305 

Fluoride  of  calcium,  ii,  342 
Focal  distance,  ii,  206 
Foetus, 

blood  of,  i,  96 

circulation  in,  ii,  286 

communication  with  mother,  ii,  268 

faeces  of,  i,  277 

membranes,  ii,  261 

office  of  bile  in,  ii,  261 

pulse  in,  i,  122 
Folds,  head  and  tail,  ii,  259 
Follicles,  Graafian,  ii,  235.    See  Graafian 

Vesicles. 
Food,  i,  212-215 

albuminous,  changes  of,  i,  247 

amyloid,  changes  of,  i,  231,  267,  285. 

of  animals,!,  220 

of  carnivorous  animals,  i,  221 

classification  of,  i,  213 

composition  of  many,  ii,  845,  et  seq. 

digestibility  of  articles  of,  i,  248 
value  dependent  on,  i,  223 

digestion  of,  in  intestines,  i,  284,  et  seq. 
in  stomach,  i,  284,  et  seq. 

improper,  i,  221 

of  man,  i,  213 

mixed,  the  best  for  man,  i,  213 
mixture  of,  necessary,  i,  214 
relation  of,  to  carbonic  acid,  produced, 
i,  194 

to  heat  of  body,  i,  311 
to  muscular  action,  ii,  44 
relation  of,  to  urea,  i,  370 
to  urine,  i,  357 

phosphates  in,  i,  363 
table  of,  i,  223 
too  little,  i,  168 
too  much,  i,  222 
vegetable,  contains  nitrogenous  priur 
ciples,  i,  216 
Foot-pound,  i,  124 
Foot-ton,  i,  124 
Foramen  ovale,  i,  106 
Forced  movements,  ii,  119 
Form  of  bodies,  how  estimated,  ii,  222 
Formation  of  fat,  ii,  66 


I  Formic  acid,  ii,  339 
Fornix,  office  of,  ii,  134 
Fourth  cranial  nerve,  ii,  138 

ventricle,  ii,  106 
Fovea  centralis,  ii,  215 
Fundus  of  bladder,  i,  354 
Fundus  of  uterus,  ii,  238 
Fungiform  papillae  of  tongue,  ii,  171 


G. 

Galactophorous  ducts,  i,  328 
Gall-bladder,  i,  272 
functions,  i,  273 

passage  of  bile  into  and  from,  i,  276 
structure,  i,  272 
Ganglia.    See  Nerve  centres, 
of  spinal  nerves,  ii,  94 
of  the  sympathetic,  ii,  151 

action  of,  ii,  153,  et  seq. 

as  co-ordinators  of  involuntary  move- 
ments, ii,  155 

structure  of,  ii,  151 
in  heart,  i,  125 

in  substance  of  organs,  ii,  155 
Ganglion,  Gasserian,  ii,  139 

corpuscles,  ii,  77 

See  Nerve-corpuscles. 
Gases,  ii,  325 

in  bile,  i,  275 

in  blood,  i,  88 

extraction  of,  i,  88 

extraction  from  blood,  i,  88 

in  stomach  and  intestines,  i,  296 

in  urine,  i,  365 
Gastric  glands,  i,  242 
Gastric  juice,  i,  245 

acid  in,  i,  246 

action  of,  on  nitrogenous  food,  i,  247 
on  non-nitrogenous  food,  i,  248 
on  saccharine  and  amyloid  princi 
pies,  i,  248 

artificial,  i,  247 
preparation  of,  i,  247 

characters  of,  i,  245 

composition  of,  i,  246 

digestive  power  of,  i,  247 

experiments  with,  i,  247 

pepsin  of,  i,  246 

quantity  of,  i,  246 

secretion  of,  i,  245 
how  excited,  i,  245 
influence  of  nervous  system  on,  i, 
252 

Gelatin,  ii,  330 
as  food,  i,  221 

action  of  gastric  juice  on,  i,  248 
action  of  pancreatic  juice  on,  i,  267 
GelatinouB  substances,  ii,  330 
Generation  and  development,  i,  234 
Generative  organs  of  tlie  female,  i,  234 

of  tlie  male,  i,  246 
Genito  urinary  tract  of  mucous  mem- 
brane, 1,  321 


INDEX. 


361 


Gerlach's  network,  ii,  92 
Germinal  area,  ii,  255 

epithelium,  ii,  235 

matter,  i,  6.    Bee  Protoplasm. 
Germinal  membrane,  ii,  254 

spot,  ii,  237 
development,  ii,  238 

vesicle,  ii,  238 

development  of,  ii,  238 

disappearance  of,  ii,  253 
Gill,  i,  172 

Gizzard,  action  of,  i,  241 
Gland,  pineal,  ii,  10 

pituitary,  ii,  10 

prostate,  ii,  246,  251 
Gland-cells,  agents  of  secretion,  i,  326 

changes  in  during  secretion,  i,  234, 
244,  264 

relation  to  epithelium,  i,  322 
Gland-ducts,  ai-ran^ement  of,  i,  326 

contractions  of,  i,  326 
Glands,  aggregate,  i,  323 

Brunner's,  i,  257 

ceruminous,  i,  339 

Cowper's,  ii,  246 

ductless,  ii,  1.    See  Vascular. 

Duverney's,  ii,  239 

of  large  intestine,  i,  268 

of  Lieberktihn,  i,  256 

lymphatic,  i,  297.     See  Lymphatic 

^  Glands. 

mammary,  1,  328 

of  Peyer,  i,  258 

salivary,  i,  226 

sebaceous,  i,  339 

secreting,  i,  322.   See  Secreting  Glands, 
of  small  intestines,  i,  257 
of  stomach,  i,  242 
sudoriferous,  i,  337 
tubular,  i,  323 

vascular,  ii,  1.    See  Vascular  Glands. 

vulvo  vaginal,  ii,  239 
Glandula  Nabothi,  ii,  239 
Glisson's  capsule,  i,  268 
Globulin,  i,  86;  ii,  328 

distinctions  from  albumin,  ii,  328 
Globus  major  and  minor,  ii,  247 

development,  ii,  300 
Glosso-pharyngeal  nerve,  i,  232;  ii,  145 

communications  of,  ii,  145 

motor  filaments  in,  ii,  146 

a  nerve  of  common  sensation  and  of 
taste,  ii,  146 
Glottis,  action  of  laryngeal  muscles  on, 
ii,  54 

closed  in  vomiting,  ii,  251 

effect  of  dirv^ision  of  pneumogastric 

nerves  on,  ii,  149 
forms  assumed  by,  ii,  55 
narrowing  of,  proportioned  to  height 

of  note,  ii,  55 
respiratory  movements  of,  i,  188 
Glucose,  ii,  339 
in  liver,  i,  282 
test  for,  i,  230 


Gluten  in  vegetables,  i,  216 
Glycerin  extract,  i,  247,  266 
Glycin,  ii,  331 
Glycocholic  acid,  ii,  331 
Glycogen,  i,  282;  ii,  339 

characters,  i,  282 

destination,  i,  282 

preparation,  i,  282 

quantity  formed,  i,  281 

variation  with  diet,  i,  281 
Glycosuria,  i,  283 

artificial  production  of,  i,  283 
Goll's  column,  ii,  96 
Graafian  vesicles,  ii,  236 

formation  and  development  of,  ii,  236, 
et  seq. 

relation  of  ovum  to,  ii,  237 

rupture  of,  changes  following,  ii,  240 
Granular  layers  of  retina,  ii,  199 
Grape-sugar,  ii,  339.    See  Glucose. 
Grey  matter  of  cerebellum,  ii,  116 

of  cerebrum,  ii,  124 

of  cruri  cerebri,  ii,  112 

of  medulla  oblongata,  ii,  109 

of  pons  Varolii,  ii,  112 

of  spinal  cord,  ii,  92 
Groove,  primitive,  ii,  256 
Growth,  i,  1 

coincident  with  development,  i,  3 

of  bone,  i,  54 

not  peculiar  to  living  beings,  i,  3 
Guanin,  ii,  334 
Gubernaculum  testis,  ii,  302 
Gullet,  i,  236 
Gustatory  nerves,  ii,  169 

cells,  ii,  173 

H. 

Habitual  movements,  ii,  87 
Hasmatin,  i,  89 

hydrochlorate  of,  i,  94 
Hsemadynamometer,  i,  150 
Hsematochometer,  i,  165 
Haematoidin,  i,  94 
Ilsemin,  i,  94 
Hsemacytometer,  i  81 
Haemoglobin,  i,  90,  et  seq. 

action  of  gases  on,  i,  93 

distribution,  i,  95 

estimation  of,  i,  95 

spectrum,  i,  92 
Hair-follicles,  i,  340 

their  secretion,  i,  343 
Hairs,  i,  339 

chemical  composition  of,  ii,  330 

structure  of,  i,  339 
Hamulus,  ii,  183 
Hare-lip,  ii,  274 

Hassall,  concentric  corpuscles  of,  ii,  6 
Haversian  canals,  i,  45 
Hearing,  anatomy  of  organ  of,  ii,  179 
double,  ii,  195 

impaired  by  lesion  of  facial  nerve,  ii^ 
144 


362 


ESTDEX. 


Hearino;,  influence  of  external  ear  on,  ii, 
179 

of  labyrinth,  ii,  191 

of  middle  ear,  ii,  187 
physiology  of,  ii,  185 

See  Sound,  Vibrations,  etc. 
Heart,  i,  103-129 
action  of,  i,  111 

accelerated,  i,  127 

effects  of,  i,  124 

force  of,  i,  122 

frequency-  of,  i,  123 

inhibited,  i,  126 

after  removal,  i,  126 

rhythmic,  i,  125 

work  of,  1,  124 
auricles  of,  1,  105,  111.    See  Auricles, 
capacity,  i,  107 
chambers,  i,  104 
chordse  tendineae  of,  i,  110 
columnae  carneee  of,  i,  105,  110 
course  of  blood  in,  i,  108 
development,  ii,  276 
endocardium,  i,  105 
force,  i,  146 
frog's,  i,  124 
ganglia  of,  i,  125 
impulse  of,  i,  119 

tracing  by  cardiograph,  i,  119,  etseq. 
influence  of  pneumogastric  nerve,  i, 
126 

of  sympathetic  nerve,  i,  127 
investing  sac,  i,  103 
muscular  fibres  of,  i,  107 
musculi  papillares,  i,  109, 113 
nervous  connections  with  other  organs, 
i,  127 
rhythm,  i,  126 
nervo\is  system,  influence  on,  i,  124 
revolution  of,  i,  117 
situation,  i,  103 
sounds  of,  i,  117 

causes,  i,  118 
structure  of,  i,  107 
tendinous  cords  of,  i,  109 
tubercle  of  Lower  in,  i,  105 
valves,  i,  109 
arterial  or  semilunar,  i,  110 

function  of,  i,  114 
auriculo- ventricular,  i.  109 
function  of,  i,  112 
ventricles,  their  action,  i,  112 

capacity,  i,  107 
weight  of,  i,  107 
work  of,  i,  124 
Heat,  animal,  i,  309.    See  Temperature, 
influence  of  nervous  system,  i,  316 
of  various  circumstances  on,  i,  309, 
et  Hcq. 

losses  by  radiation,  etc.,  1,  313 

in  relation  to  bile,  i,  278 
sources  and  modes  of  production,  i.  312 
developed  in  contraction  of  muscles,  i, 

309.  312 
perception  of,  ii,  KK} 


Heat  centres,  i,  316 
Heat-producing  tissues,  i,  312 
Heat  or  rut,  ii,  240 

analogous  to  menstruation,  ii,  240 
Height,  relation  to  respiratory  capacity, 

i.  189 
Helicotrema,  ii,  183 
Helix  of  ear,  ii,  179 
Hemipeptone,  ii,  329 
Hemispheres,  Cerebral,  ii,  120.    See  Cere- 
brum. 
Hepatic  cells,  i,  268 

ducts,  i,  271 

veins,  i,  270 
characters  of  blood  in,  i,  87 

vessels,  arrangement  of,  i,  269,  et  seq. 
Herbivorous  animals, 

perception  of  odors  by,  ii,  178 
Hering's  theory,  ii,  224 
Hermaphroditism,  apparent,  ii,  305 
Hibernation,  state  of  thymus  in,  ii,  6 
Hiccough,  mechanism  of,  i,  200 
Hip-joi  't,  pain  in  its  diseases,  ii,  84 
Hippuric  acid,  i,  361,  372;  ii,  332 
Horse's  blood,  peculiar  coagulation  of,  1, 
66 

Howship's  lacunse,  i,  44 

Hunger,  sensation  of,  i,  218 

Hyaline  cartilage,  i,  38 

Hydrogen,  ii,  325 

Hydroiytic  ferments,  i,  230;  ii,  335 

Hymen,  ii,  239 

Hypersesthesia, 

result  of  injury  to  spinal  cord,  ii,  99 
Hypermetropia,  ii,  212 
Hypoblast,  ii,  255 
Hypoglossal  nerve,  ii,  150 
Hypospadias,  ii,  305 
Hypoxanthin,  ii,  334 


I. 

Ideas,  connection  of,  with  cerebrum,  ii, 

128 
Ileum,  i,  254 
lleo-ceecai  valve,  i,  263 
Illusions  of  touch,  i,  165 
Image,  formation  of,  on  retina,  ii,  204 

distinctness  of,  ii,  211 

inversion  of.  ii,  218 
Impulse  of  heart,  i,  119 
Income  of  body,  ii,  64 

compareil  with  expenditure,  ii,  64 
Incus, 

function  of,  ii,  181 
Indican,  i,  362  \ 
Indigo,  ii,  335 
Indol,  i,  267 
Induction 

coil,  ii,  27 

cum>nt,  ii.  27 
Infundibulum,  i,  180 
Inhibitory  influence    i  pneumogastric 
nerve,  i,  126 


INDEX. 


363 


Inhibitory  action  of  brain,  ii,  102 
nerves,  ii,  80 
action  of,  on  heart,  i,  126 
on  blood-vessels,  i,  155 
on  blood-vessels  of  salivary  glands, 

i,  232,  et  seq. 
0-1  gastric  blood-vessels,  i,  252,  et 
seq. 

on  intestinal  movements,  i,  289 
on  respiratory  movements,  i,  201 
Inhibitory  heat-ceutre,  i,  316 
Inorgani  •  matter,  distinction  from  or- 
ganized, ii,  326,  et  seq. 

pri  ciples,  ii,  340 
Inosite,  ii,  339 
Insalivation,  i,  226 
Inspiration,  i,  183 

e  astic  resistance  overcome  by,  i,  191 

extraordinary,  i,  1^86 

force  employed  in,M,  191 
during  dyspnoea,  i,  209 

influence  o  ,  on  circulation,  i,  205 

mechanism  of,  i,  183 
Intercellular  substance,  i,  17 
Intercostal  muscles,  action  in  inspiration, 
i,  185,  et  seq. 

in  expiration,  i,  186 
Interlobular  veins,  i,  271 
Intestinal  juice,  i,  283 
Intestine^,  digestion  in,  i,  284,  286 

deve  opment,  ii,  295 

fatty  discharges  from,  i,  267 

gases,  i,  296 

large,  digestion  in,  i,  286 
structure,  i,  262 

length  in  different  animals,  i,  284 

movements,  i,  289 

small,  changes  of  food  in,  i,  284 
structure  of,  i,  254 
Intonation,  ii,  57,  et  seq. 
Intralobular  veins,  i,  271 
Inversive  torments,  i,  284 
Involuntary  muscles, 

actions  <  f,  i,  251 

s  ructure  of,  ii,  14 
Iris,  ii,  205 

action  of,  ii,  205,  et  seq. 
in  adaptation  to  distances,  ii,  209 

blood-vessels,  ii,  205 

development  of,  ii,  293 

influence  of  fifth  nerve  on,  ii,  206 
of  third  nerve,  ii,  206 

relation  of,  to  optic  nerve,  ii,  206 
Iron,  ii,  342 
Irradiation,  ii,  214 
Ivory  of  teeth,  i,  57 


J. 

Jacob's  membrane,  ii,  201 

Jacobson's  nerve,  ii,  145 

Jaw,  interarticular  cartilage,  1,  "226 

Jejunum,  i,  254 

Juice,  gastric,  i,  245 


Juice,  pancreatic,  i,  266 
Jumping,  ii,  43 


K. 

Karyokinesis,  i,  13 
Katacrotic  wave,  i,  146 
Katelectrotonus,  ii,  47 
Ker  tin,  i,  248 
Key,  ii,  27 

Kidneys,  their  structure,  i,  347 

blood-vessels  of,  how  distributed,  i,  352 

capillaries  of,  i,  343 

development  of,  ii,  299 

function  of,  i,  355.    See  Urine. 

Malpighian  corpuscles  of,  i,  348 

nerves,  i,  353 

tubules  of,  i,  348 
Knee,  pain  of,  in  diseased  hip,  ii,  84 
Krause's  membrane,  ii,  17 
Kreatinin,  i,  363 
Kymograph,  i,  150 

tracings,  i,  149,  et  seq. 

spring,  i,  150 


L. 

Labia  externa  and  interna,  ii,  239 
Labyrinth  of  the  ear,  ii,  182,  et  seq. 

membranous,  ii,  185 

osseous,  ii,  182 

function  of,  ii,  191 
Lachrymal  apparatus,  ii,  196 

gland,  ii,  196 
Lactation,  i,  329 
Lacteals,  i,  291 

absorption  by,  i,  308 

contain  lymph  in  fasting,  i,  301 

origin  of,  i,  292 

structure  of,  i,  293 

in  villi,  i,  259 
Lactic  acid,  ii,  840 

in  gastric  fluid,  i,  246 
Lactiferous  ducts,  i,  329 
Lactose,  i,  215,  381 
Lacunae  of  bone,  i,  44 
Lamellae  of  bone,  i,  46 
Lamina  spiralis,  ii,  183 

use  of,  ii,  192 
Laminae  dorsales,  ii,  256 

viscerales  or  ventrales,  ii,  261 
Language,  how  produced,  ii,  60 
Large  intestine,  i,  261.    See  Intestine. 
Larynx,  construction  of,  ii,  51 

muscles  of,  ii,  58 

nerves  of,  ii,  58 

variations  in,  according  to  sex  and  age, 
ii,  58 

ventricles  of,  ii,  60 

vocal  cords  of,  ii,  52 
Latent  period,  ii,  82 
Laughing,  i,  201 
Laxator  tympani  muscle,  ii,  191 


364 


INDEX. 


Lead  an  accidental  element,  ii,  343 
Leaping,  i,  44 
Lecithin,  i,  275 

Legumen  identical  with  casein,  i,  216 

Lens,  crystalline,  ii,  204 

Lenticular  ganglion,  relation  of  third 

nerve  to,  ii,  141 
Leucic  acid,  ii,  340 
Leucin,  i,  266 
Leucocytes, 

of  blood,  i,  79 

amceboid  movements,  1,  80 

chyle,  i,  301 

lyniph,  i,  300 

origin  of,  i,  99 
Leucocythsemia,  state  of  vascular  glands 
in,  ii,  3 

Levers,  different  kinds  of,  ii,  39 
Lieberklihn 's  glands, 

in  large  intestines,  i,  263 

in  small  intestines,  i,  256 
Life,  ii,  820 

relation  to  other  forces,  ii,  306 

simplest  manifestations  of,  i,  7 
Ligamentum  nuchge,  i,  33 
Lightning,  condition  of  blood  after  death 
by,  i,  72 

Lime,  salts  of,  in  human  body,  ii,  342 
Lingual  branch  of  fift  i  nerve,  i,  231 
Lips,  influence  of  fifth  nerve  on  move- 
ments of,  ii,  141 
Liquor  amuii,  ii,  263 
Liquor  sanguinis,  or  plasma,  i,  63 

lymph  derived  from,  i,  302 

still  layer  in  capillaries,  i,  158 
Liver,  i,  268 

action  of,  on  albuminous  matters,  1,  280 
on  saccharine  matters,  i,  281 

blood-elaborating  organ,  i,  280 

blood-making  organ,  i,  97 

blood-vessels  of,  i,  271 

capillaries  of,  i,  271 

cells  of,  i,  269 

circulation  in,  i,  269 

development  of,  ii,  297 

ducts  of,  i,  271 

functions  of,  i,  273 
in  foetus,  i,  277 

glycogenic  function  of,  i,  280 

secretion  of,  i,  273.    See  Bile. 

structure  of,  i,  268 

sugar  formed  by,  i,  282,  et  seq. 
Locus  niger,  ii,  113 
Loss  of  water,  ii,  341 
Ludwig's  air  pump,  i,  89 
Lungs,  i,  178 

blood  su))ply,  i,  182 

capillaries  of,  i,  134 

cells  of,  i,  179 

changes  of  air  in,  i,  192 

changes  of  blood  in,  i,  197 

circulation  in,  i,  182 

contraction  of,  i,  192 

coverings  of,  i,  179 

development  of,  ii,  298 


Lungs,  elasticity  of,  i,  187 

lobes  of,  i,  179 

lobules  of,  i,  179 

lymphatics,  i,  182 

muscular  tissue  of,  1,  192 

nerves,  i,  182 

nutrition  of,  i,  182 

position  of,  i,  173 

structure  of,  i,  179 
Luxus  consumption,  1,  222 
Lymph,  i,  301 

compared  with  chyle,  i,  301 
with  blood,  i,  302 

current  of,  i,  297 

quantity  formed,  i,  302 

source  of,  i,  303 
Lymph -corpuscles,  i,  301 

in  blood,  i,  99 

development  of  into  red  blood-corpus- 
cles, i,  99 
origin  of,  i,  99 
Lymph-hearts,  structure  and  action  of, 
i,  304 

relation  of  to  spinal  cord,  i,  305 
Lymphatic  glands,  i,  297 
Lymphatic  vessels,  i,  291 

absorption  by,  i,  303 

communication  with  serous  cavities, 
i,  293 

communication  with  blood- ves£,t;k,  i, 
293 

contraction  of,  i,  297 
course  of  fluid  in,  i,  297 
distribution  of,  i,  291 
origin  of ,  i,  292 

propulsion  of  lymph  by,  i,  297 
structure  of,  i,  297,  et  seq. 
valves  of,  i,  297 
Lymphoid  or  retiform  tissue,  i,  34  See 
Adenoid  Tissue. 

M. 

Macula  germinativa,  ii,  237 
Magnesium,  ii,  342 
Male  sexual  functions,  ii,  246 
Malleus,  ii,  180 

function  of,  ii,  188 
Malpighian  bodies  or  corpuscles  of  kid^ 
ney,  i,  349 

capsules,  i,  350 

corpuscles  of  spleen,  ii,  4 
IMaltose,  i,  231;  ii,  336 
Mammalia, 

blood  corpuscles  of.  i,  77 

brain  of.  ii.  126 
i\Iammary  glands,  i,  328 

evolution,  i,  330 

involution,  i,  330 

lactation,  i,  329 
IMandibular  arch,  ii,  274 
Manganese,  ii,  343 
iMan'onietcr,  i.  149 

cxiHM-iments  on  respiratory  power  with, 
i,  192 


INDEX. 


365 


Marrow  of  bone,  i,  43 
Mastication,  i,  225 

fifth  nerve  supplies  muscles  of,  i,  226 

muscles  of,  i,  226 
Mastoid  cells,  ii,  180 
Matrix  of  cartilage,  i,  38 

of  nails,  i,  341 
Mature  corpuscles, 

origin  of,  i,  97 
Meatus  of  ear,  ii,  179 

urinarius,  opening  of  in  female,  ii,  239 
Meckel's  cartilage,  ii,  274 
Meconium,  i,  277 
^Medulla  of  bone,  i,  43 

of  liair,  i,  340 
Medulla  oblongata,  ii,  105 

columns  of,  ii,  105 

conduction  of  impressions,  ii,  109 

decussation  of  fibres,  ii,  106 

development,  ii,  289 

effects  of  injury  and  disease  of,  ii, 
110 

fibres  of,  how  distributed,  ii,  106 
functions  of,  ii,  109,  et  seq. 
important  to  life,  ii,  110 
nerve  centres  in,  ii,  110 
pyramids  of,  anterior,  ii,  106 

posterior,  ii,  107 
structure  of,  ii,  106 
Medullary  portion  of  kidney,  i,  349 
substance  of  lymphatic  glands,  i,  297 
substance  of  nerve  fibre,  ii,  71 
Melanin,  ii,  335 
Membrana  decidua,  ii,  243 
granulosa,  ii,  236 
development  of  into  corpus  luteum, 
ii,  243 
limitans  externa,  ii,  201 
interna,  ii,  200 
Membrana  propria  or  basement  mem-' 
brane,  i,  322.    See  Basement  Mem- 
brane, 
pupillaris,  ii,  293 

capsulo-pupillaris,  ii,  293 
tympani,  ii,  180 
office  of,  ii,  187 
Membrane,  blastodermic,  ii,  254 
Jacob's,  ii,  201 

of  the  brain  and  spinal  cord,  ii,  88 
ossification  in,  i,  47 
primary  or  basement,  i,  319.   See  Base- 
ment membrane, 
vitelline,  ii,  237 
Membranes,  mucous,  i,  321.    See  Mucous 

membranes. 
Membranes,  passage  of  fluids  through,  1, 
296 

secreting,  i,  322 
JMembranes,  serous,  i,  319.    See  Serous 

membranes. 
Membranous  labyrinth,  ii,  185 
Memory,  relation  to  cerebral  hemispheres, 

ii,  127,  et  seq. 
Menstrual  discharge,  composition  of,  ii, 

242 


Menstruation,  ii,  240 

coincident  with  discharge  of  ova,  ii,  241 
corpus  luteum  of,  ii,  243 
time  of  appearance  and  cessation,  ii, 
243 

Mental  derangement,  ii,  128 
exertion,  effect  on  heat  of  body,  i,  316 

on  phosphates  in  urine,  i,  363 
faculties,  development  of  in  proportion 
to  brain,  ii,  128 
theory  of  special  localization  of,  ii, 
129,  et  seq 
field  of  vision,  ii,  220 
Mercurial  air-pump,  i,  89 
Mercurial  manometer,  i,  148 
Mercury,  absorption  of,  i,  345 
Mesencephalon,  ii,  290 
Mesenteric  veins,  blood  of,  i,  88 
Mesoblast,  ii,  255 
Mesocephalon,  ii,  112 
Metalbumin,  ii,  328 

Metallic  substances,  absorption  of  by 

skin,  i,  345 
Metencephalon,  ii,  290 
Metbsemoglobin,  i,  93 
Mezzo-soprano  voice,  ii,  57 
Micturition,  i,  373 
Milk,  as  food,  i,  248 

chemical  composition,  i,  331 

secretion  of,  i,  329 
Milk- curdling  ferments,  i,  267,  332 
Milk-globules,  i,  331 
Milk-teeth,  i,  62,  et  seq. 
Millon's  re- agent,  ii,  327 
Mind,  cerebral  hemisphere  the  organs  of, 
ii,  127 

influence  on  action  of  heart,  i,  124 
influence  on  animal  heat,  i,  316 

on  digestion,  i,  290 

on  hearing,  ii,  194 

on  movements  of  intestines,  i,  290 

on  secretion,  i,  327 

on  secretion  of  saliva,  i,  232 

in  vision,  ii,  220,  et  seq. 
power  of  concentration  on  the  senses, 
ii,  223 

of  exciting  sensations,  ii,  160 
Mitral  valve,  i,  107 
Modiolus,  ii,  183 
Molecules,  or  granules,  i,  7 

in  blood,  i,  75 

in  milk,  i,  832 

movement  of  in  cells,  i,  7 
Molars,  i,  61 

Molecular  base  of  chyle,  i,  301 

motion,  i,  7 
Monamides,  ii,  331 

Motion,  causes  and  phenomena  of.  ii,  12 
amoeboid,  i,  7,  80;  ii,  13 
ciliary,  i,  7;  ii,  12 
molecular,  i,  7 
muscular,  ii,  24,  et  seq. 
of  objects,  how  judged,  ii,  223 
power  of,  not  essentially  distinctive  of 
animals,  i,  3 


366 


INDEX. 


Motion,  sensation  of,  ii,  161 
Motor  impulses,  transmission  of  in  cord, 
ii,  99 

nerve-fibres,  ii,  80 
laws  of  action  of,  ii,  83 
Motor  linguae  nerve,  ii,  150 

oculi,  or  third  nerve,  ii,  137 
Motorial  end-plates,' ii,  76 
Mouth,  changes  of  food  in,  i,  224,  et  seq. 
IVFovements, 

of  eyes,  ii,  228 

of  intestines,  i,  290 

of  voluntary  muscles,  ii,  39 

produced  by  irritation  of  auditory 
nerve,  ii,  195 
Mucigen,  i,  235 
Mucin,  i,  235 
Mucous  membrane,  i,  321 

basement  membrane  of,  i,  322 

capillaries  of,  i,  134 

epithelium-cells  of,  i,  322.   See  Epithe- 
lium, 

digestive  tract,  i,  321 
gastro-pulmonary  tract,  i,  321 
genito- urinary  tract,  i,  321 
gland-cells  of,  i,  322 
of  intestines,  i,  254,  261 
of  stomach,  i,  241 
of  tongue,  ii,  169 

of  uterus,  changes  of  in  pregnancy,  ii, 
265 

respiratory  tract,  i,  321 
Muco-salivary  glands,  ii,  229 
Mucus,  i,  322 

in  bile,  i,  275 

in  urine,  i,  362 

of  mouth,  mixed  with  saliva,  i,  229 
Muller's  fibres,  ii,  203 
Murexide,  i,  361;  ii,  334 
Muscles, 

activity,  ii,  24 

changes  in,  by  exercise,  ii,  34 

chemical  constitution,  ii,  21,  35 

clot,  ii,  21 

contractility,  ii,  24 

contraction,  mode  of,  ii,  29 

corpuscles,  ii,  18 

curves,  ii,  32,  et  seq. ;  ii,  36 

development,  ii,  20 

disc  of  Hensen,  ii,  18 

effect  of  pressure  of,  on  veins,  i,  162 

elasticity,  ii,  20 

electric  currents  in,  ii,  22,  35 

fatigue,  ii,  33 

curves,  ii,  33 
growth,  ii,  20 
heart,  ii,  19 

heat  developed  in  contraction  of,  ii, 
34 

involuntary,  ii,  14 

actions  of,  ii.  36,  44 
Krause's  membrane,  ii,  17 
muscle-rods,  ii,  19 
natural  currents,  ii,  22 
nerves  of,  ii,  20 


Muscles,  non-striated,  ii,  14 
nutrition  of,  ii,  19 
physiology  of,  ii,  20 
plain,  ii,  14 
plasma,  ii,  21 
reaction,  ii,  21 
response  to  stimuli,  ii,  36 
rest  of,  ii,  20 
rigor,  ii,  37 
sarcolemma,  ii,  16 
sensibility  of,  ii,  25 
serum,  ii,  22 
shape,  changes  in,  ii,  35 
sound  developed  in  contraction  of,  ii, 
34 

source  of  action  of,  ii,  44 
stimuli,  ii,  25 
striated,  ii,  15 
str  cture,  ii,  16,  et  seq. 
tetanus,  ii,  32 
unstriped,  ii,  14 
voluntary,  ii,  15 
actions  of,  ii,  39 

blood-vessels  and  nerves  of,  ii,  19 

work  of,  ii,  33 
Muscular  action,  ii,  36 

conditions  of,  ii,  36 

force,  ii,  33 

source,  ii,  44 
Muscular  irritability,  ii,  36 

duration  of,  after  death,  ii,  37 
Muscular  motion,  ii,  14 

sense,  ii,  164 
cerebellum  the  organ  of,  ii,  119 

tone,  ii,  104 
Muscularis  mucosae,  i,  237,  242,  255 
Musculi  papillares,  i,  110 
Musculo-cutaneous  plate,  ii,  272 
Musical  sounds,  ii,  193 
Myograph,  ii,  30 

pendulum,  ii,  30 
Myopia,  or  short-sight,  ii,  212 
Myosin,  ii,  21 


N. 

Nabothi  glandulae,  ii,  239 
Nails,  i,  341 

growth  of,  i,  341 

structure  of,  i,  341 
Naphthilamine,  i,  267 
Nasal  cavities  in  relation  to  smell,  tx  176. 
et  seq. 

Native  albumins,  ii,  327 

Natural  organic  compounds,  ii,  326 

classilication  of.  ii.  326 
Nerve-centre,  ii,  74.     See  Cer  bellum, 
Cerebrum,  etc. 

ano-spinal.  ii.  103 

automatic  action,  ii,  88 

car  ,io-inhil)itory,  i,  127;  ii.  111 

cilio-sjiinal,  ii.  109 

condiu'tion  in,  ii,  83 

deglutition,  i,  240;  ii.  Ill 


INDEX 


367 


Nerve-centre,  diabetic,  ii.  111 

diffusion  in,  ii,  84 

functions  of,  ii,  83 

genito-urinary,  ii,  103 

mastication,  i,  226;  ii,  111 

radiation  in,  ii,  85 

reflexion  in,  ii,  85 
laws  and  conditions  of,  ii,  85 

respiratory,  i,  202;  ii,  110 

secretion  of  saliva,  i,  232;  ii,  111 

transference  of  impressions,  ii,  84 

vaso-motor,  i,  154;  ii,  111 

vesico-spinai,  ii,  103 
Nerve-corpuscles, 

caudate  or  stellate,  ii,  78 

polar,  ii,  78 
Nerves,  ii,  68 

accelerator,  i,  128 

action  of  stimuli  on,  ii,  46 
currents  of,  ii,  45 

affeient,  ii,  80 

axis-cylinder  of,  ii,  70 

centrifugal,  ii,  80 

centripetal,  ii,  80 

cerebro-spinal,  ii,  68 

classification,  ii,  70,  80 

conduction  by,  ii,  80,  et  seq. 
rate  of,  ii,  81 

continuity,  ii,  73 

course  of,  ii,  73 

cranial,  ii,  136.    See  Cerebral  Nerves, 
depressor,  i,  154 
efferent,  ii,  80 
electrical  currents  of,  ii,  45 
functions  of,  ii,  78 
effect  of  chemical  stimuli  on,  ii,  46 

of  mechanical  irritation,  ii,  46 

of  temperature,  ii,  46 
funiculi  of,  ii,  69 
grey,  ii,  71 

impressions  on,  referred  to  periphery, 
ii,  81 

inhibitory,  ii,    80.     See  Inhibitory 

Action, 
intercentral,  ii,  80 
laws  of  conduction,  ii,  81 

of  motor  nerves,  ii,  83 

of  sensory  nerves,  ii,  81 
medullary  sheath,  ii,  69 
medullated,  ii,  69 
motor,  ii,  80 

laws  of  action  in,  ii,  82 
natural  currents,  ii,  45 
neurilemma,  ii,  69 
nodes  of  Ranvier,  ii,  71 
non-medullated,  ii,  71 
nuclei,  ii,  70 
of  special  sense,  ii,  82 
plexuses  of,  ii,  73 
primitive  nerve  sheath,  ii,  70 
sensory,  ii,  80 

laws  of  action  in,  ii,  81 
size  of,  ii,  80 

spinal,  ii,  94,  96, 150,  et  seq.   See  Spinal 
Nerves. 


Nerves,  stimuli,  ii,  46 
structure,  ii,  69 

sympathetic,  ii,  68,  151.    See  Sympa- 
thetic Nerve, 
terminations  of,  ii,  76 

central,  ii,  77 

in  cells,  ii,  76 

in  end-bulbs,  ii,  74 

in  motorial  end-plates,  ii,  76 

in  networks  or  plexuse-^,  ii,  76 

in  Pacinian  corpuscles,  ii,  74 

in  touch -corpuscles,  ii,  75 
trophic,  ii,  142,  157 
ulnar,  effect  of  compression  of,  ii,  81 
varieties  of,  ii,  69 
vaso-constrictor,  i,  156 
vaso-dilator,  i,  156 
vaso-inhibitory,  i,  156 
vaso-motor,  i,  156 
white,  ii,  46 
Nervi  nervo  um,  ii,  82 
Nervi  vasorum,  i,  132 
Nervous  force,  velocity  of,  ii,  80 
Nervous  system,  ii,  68 
cerebro-spinal,  ii,  68 
development,  ii,  287 
elementary  structure  of,  11,  68 
influence  of 

on  animal  heat,  i,  316 

on  arteries,  i,  154,  et  seq. 

on  contractility,  ii,  24 

on  contraction  of  blood-vessels,  i, 
152 

on  erection,  i,  169 

on  gastric  digestion,  i,  252 

on  the  heart's  action,  i,  124 

on  movements  of  intestines,  1,  289 

of  stomach,  i,  252 
on  nutrition,  ii,  157 
on  respiration,  i,  201 
on  secretion,  i,  231 
on  sphincter  ani,  i,  288 
sympathetic,  ii,  151. 

Network,  intracellular,  i,  10 
nuclear,  i,  11 

Neurilemma,  ii,  69 

Neurin,  ii,  332 

Neuroglia,  i,  34 

Nipple,  an  erectile  organ,  i,  168 
j     structure  of,  i,  329 

Nitrogen, 
I     in  blood,  i,  96 

1     influence  of,  in  decomposition,  ii,  326 

I     in  relation  to  food,  i,  213,  et  seq.  • 

I     in  respiration,  i,  195 

;  Nitrogenous  compounds,  i,  213 

j     non-nitrogenous  compounds,  i,  213 

Nitrogenous  equilibrium,  ii,  66 

Nitrogenous  food,  i,  214 
!     in  relation  to  muscular  work,  i,  370,  et 
I  seq. 

j     in  relation  to  urea,  i,  370 

to  uric  acid,  i,  372 
:  Nodes  of  Ranvier,  ii,  71 
I  Noises  in  ears,  ii,  83 


3G8 


INDEX. 


Non-azotized  or  Non-nitrogenous  food,  i, 
313 

organic  principles,  ii,  335 
Nose,  ii,  175.    See  Smell. 

irritation  referred  to,  ii,  85 
Notochord,  ii,  257 
Nucleus,  i,  10 

position,  i,  11 

staining  of,  i,  11 
Nutrition,  ii,  63 

general  nature, 

of  nervous  system,  ii,  155 
of  trophic  nerves,  ii,  157 

in  paralyzed  parts,  ii,  157 

of  cells,  i,  9 
Nymphae,  ii,  339 


O. 

Ocular  cleft,  ii,  293 

spectrum,  ii,  225,  et  seq. 
Odontoblasts,  i,  59 
Odors, 

causes  of,  ii,  77,  et  seq 

different  kinds  of,  ii,  178 

perception  of,  ii,  178 
varies  in  different  classes,  ii,  178 

relation  to  taste,  ii,  174 
(Esophagus,  i,  236 
Oil,  absorption  of,  i,  303 
Oleaginous  principles,  digestion  of,  i,  331 
Oleic  acid,  ii,  339 
Olfactory  cells,  ii,  176 

nerve,  ii,  175 
subjective  sensations  of,  ii,  179 
Olivary  hody,  ii,  106 

fasciculus,  ii,  106 
Omphalo-mesenteric, 

arteries,  ii,  281 

duct,  ii,  270 

veins,  ii,  281 
Oncograph,  i,  367 
Oncometer,  i,  366 

Ophthalmic  ganglion,  relation  of  third 

nerve,  ii,  137 
Ophthalmoscope,  ii,  217 
Optic, 

lobes,   corpora  quadrigemina,  homo- 
logues  of,  ii,  114 
functions  of,  ii,  114 
nerve,  decussation  of,  ii,  231 
point  of  entrance  insensible  to  light, 
ii,  215 

thalamus,  function  of,  ii,  115 

vesicle,  primary,  ii,  291 
secondary,  ii,  292 
Optical  angle,  ii,  220 

apparatus  of  eye,  ii,  203 
Ora  serrata  of  retina,  ii,  199 
Oraiig, 

brain  of,  ii,  127 
Organ  of  Corli,  ii,  184 
Orgunic  compounds  in  body,  ii,  325 

instability  of,  ii,  326 


Organs,  plurality  of  cerebral,  ii,  129 

Organs  of  sense,  development  of,  ii,  391 

Osmosis,  i,  306 

Os  orbiculare,  ii,  181 

Os  uteri,  ii,  239 

Osseous  labyrinth,  ii,  183 

Ossicles  of  the  ear,  ii,  181 

office  of,  ii,  188 
Ossicula  auditis,  ii,  181 
Ossification,  i,  47,  et  seq. 
Osteoblasts,  i,  48 
Osteoclasts,  i,  51 
Otoconia  or  Otoliths,  ii,  185 

use  of,  ii,  191 
Ovaries,  ii,  235 

enlargement  of,  at  puberty,  ii,  238 

Graafian  vesicles  in,  ii,  336 
Ovisacs,  ii,  336 
Ovum,  ii,  336 

action  of  seminal  fluid  on,  ii,  353 

changes  of,  in  ovary,  ii,  338 

previous  to  formation  of  embryo, 
ii,  353 

subsequent  to  cleavage,  ii,  355,  et 
seq. 

in  uterus,  ii,  354,  et  seq. 
cleaving  of  yelk,  ii,  353 
connection  of  with  uterus,  ii,  335 
discharge  of  from  ovary,  ii,  339 
formation  of,  ii,  338 
germinal  membrane  of,  ii,  354 
germinal  vesicle  and  spot  of,  ii,  337 
impregnation  of,  ii,  353 
structure  of,  ii,  336 
unimpregnated,  ii,  336 

Oviduct,  or  Fallopian  tube,  ii,  338 

Oxalic  acid,  i,  365 

Oxalic  acid  in  urine,  i,  365 

Oxygen,  ii,  335 
in  blood,  i,  89 

consumed  in  breathing,  i,  195 
effects  of  on  color  of  blood,  i,  88 
proportion  of  to  carbonic  acid,  i,  19^  . 

et  seq. 

Oxyh?emoglobin,  i,  92 
spectrum,  i,  92 


P. 

Pacinian  bodies  or  corpuscles,  ii,  74 
Palate  and  uvula  in  relation  to  voice,  ii, 
59 

cleft,  ii,  274 
Palmitiu,  ii,  338 
Pancreas,  i,  264 

development  of,  ii,  297 

functions  of,  i,  264 

structure,  i.  264 
Pancreatic  fluid,  i,  265 
Pancreatin,  ii,  337 
PapiHa  foliata,  ii,  173 
Papilhe 

of  the  kidney,  i,  348 

of  skin,  distribution  of,  i,  335 


INDEX. 


369 


Papillae,  end-bulbs  in,  i,  337 
epithelium  of,  i,  335 
nerve-fibres  in,  i,  336 
supply  of  blood  to,  i,  336 
touch  corpuscles  in,  i,  337 
of  teeth,  i,  59 
of  tongue,  ii,  169,  et  seq. 
circum vallate  or  calyciform,  ii,  176 
conical  or  filiform,  ii,  171 
fungiform,  ii,  171 
Paraglobulin,  i,  70 
Paralbumin,  ii,  328 

Par  vaguni,  ii,  146.    See  Pneumogastric 

nerve. 
Paralyzed  parts, 

nutrition  of,  ii,  157 
pain  in,  ii,  82 

limbs,  temperature  of,  i,  316 

preservation  of  sensibility  in,  ii,  99 
Paralysis,  cross,  ii,  99 
Parapeptone,  i,  248 
Paraplegia, 

delivery  in,  ii,  103 

reflex  movements  in,  ii,  103 

state  of  intestines  in,  i,  290 
Parotid  gland,  saliva  from,  i,  226,  234 

nerves  influencing  secretion  by,  i,  234 
Pause  in  heart's  action,  i,  117 

respiratory,  i,  188 
Pecten  of  birds,  ii,  292 
Peduncles, 

of  the  cerebellum,  ii,  118 

of  the  cerebrum,  or  Crura  Cerebri,  ii, 
113 

Pelvis  of  the  kidney,  i,  348 
Penis, 

corpus  cavernosum  of,  i,  168 

development  of,  ii,  305 

erection  of,  explained,  i,  169 

reflex  action  in,  ii,  103 
Pepsin,  i,  244 
Pepsinogen,  i,  244 
Peptic  cells,  i,  242 
Peptones,  i,  247,  et  seq. 
Perceptions  of  sensations  by  cerebral 

hemispheres,  ii,  128 
Pericardium,  i,  103 
Perichondrium,  i,  49 
Perilymph,  or  fluid  of  labyrinth  of  ear, 
ii,  182 

use  of,  ii,  191 
Perimysium,  ii,  15 
Perineurium,  ii,  69 
Periosteum,  i,  43 

Peristaltic  movements  of  intestines,  i,  289 

of  stomach,  i,  249 
Perivascular  lymphatic  sheaths,  i,  139 
Permanent  teeth,  i,  62.    See  Teeth. 
Perspiration,  cutaneous,  i,  343 

inr-;ensible  and  sensible,  i,  343 

ordinary  constituents  of,  i,  343 
Peyer's  glands,  i,  258 

patches,  i,  258 

resemblance  to  vascular  glands,  ii,  1 
structure  of,  i,  259 
Vol.  II.— 24. 


Pflliger's  law,  ii,  48 
Phakoscope,  ii,  208 
Pharynx,  i,  236 

action  of  in  swallowing,  i,  239 

influence  of  glosso-pharyngeal  nerve 
on,  i,  239 
of  pneumogastric  nerve  on,  i,  239 
Phenol,  ii,  340 
Phosphates,  ii,  342 
Phosphates  in  tissues,  ii,  343 
Phosphorus  in  the  human  body,  ii,  342 
Pia  mater,  circulation  in,  i,  167 
Pigment,  i,  21 

of  hair,  i,  339 

of  retina,  ii,  202 

of  skin,  i,  334 
Pigment  cells,  forms  of,  i,  21 

movements  of  granules  in,  i,  21 
Pineal  gland,  ii,  10 
Pinna  of  ear,  ii,  179 
Pituitary  body,  ii,  10 

development,  ii,  272 
Placenta,  ii,  265,  et  seq. 

foetal  and  maternal,  ii,  265 
Plants, 

distinctions  from  animals,  1,  3.  See 
also  Vegetables. 
Plasma  of  blood,  i,  65 

salts  of,  i,  85 
Plasmine,  i,  68 
composition,  i,  69 
nature  of,  i,  68 
Plethysmograph,  i,  153 
Pleura,  i,  178 
Plexus,  terminal,  ii,  76 

of  spinal  nerves,  relation  to  cord,  ii,  73 
myentericus,  i,  255 
Auerbach's,  i,  255 
Meissner's,  i,  255 
Pneumogastric  nerve,  ii,  146 
distribution  of,  ii,  146 
influence  on 

action  of  heart,  i,  126 
deglutition,  i,  239 
gastric  digestion,  i,  253 
larynx,  i,  239 
lungs,  i,  202 
oesophagus,  ii,  147 
pharynx,  ii,  146 
respiration,  i,  202 
secretion  of  gastric  fluid,  i,  252 
sensation  of  hunger,  i,  218 
stomach,  i,  252 
mixed  function  of,  ii,  146 
origin  from  medulla  oblongata,  ii,  108 
Poisoned  wounds,  absorption  from,  i,  308 
Pons  Varolii,  its  structure,  ii,  112 

functions,  ii,  112 
Portal, 
blood,  characters  of,  i,  87 
canals,  i,  271 
circulation,  i,  269 
function  of  spleen  with  regard  to, 
ii,  4 

veins,  arrangement  of,  i,  271,  et  seq. 


370 


ESTDEX. 


Portio  dura,  of  seventh  nerve,  ii,  144 

mollis,  of  seventh  nerve,  i;,  185 
Post  mortem  digestion,  i,  253 
Potassium,  ii,  342 

sulphocyanate,  i,  229 
Pregnancy,  absence  of  menstruation  dur- 
ing, ii,  243 

corpus  luteum  of,  ii,  245 

influence  on  blood,  i,  86 
Presbyopia,  or  long-sight,  ii,  214 
Primitive  groove,  ii,  256 
Primitive  nerve-sheath,   or  Schwann's 

sheath,  ii,  71 
Processus  gracilis,  ii,  181 
Propionic  acid,  ii,  339 
Prosencephalon,  ii,  289 
Prostate  gland,  ii,  246 
Proteids,  i,  247 

chemical  properties,  ii,  327,  et  seq. 

physical  properties,  ii,  327 

tests  for,  ii,  327 

varieties  of,  ii,  328 
Proteolytic  ferments,  i,  248 
Protoplasm,  i,  6 

chemical  characters,  i,  6 

movement,  i,  6 

nutrition,  i,  9 

physical  characters,  i,  6 

physiological  characters,  i,  6 

reproduction,  i,  11 

transformation  of,  i,  14 
Proto-vertebrse,  ii,  258 
Pseudoscope,  ii,  233 
Ptyalin,  i,  229 

action  of,  i,  229 
Puberty, 

changes  at  period  of,  ii,  243 

indicated  by  menstruation,  ii,  243 
Pulmonary  artery,  valves  of,  i,  110 

capillaries,  i,  134 

circulation,  i,  182 
Pulse,  arterial,  i,  142 

cause  of,  i,  142 

dicrotus,  i,  146 

difference  of  time  in  different  parts,  i, 
143 

frequency  of,  i,  122 

influence  of  age  on,  i,  122 
of  food,  posture,  etc.,  i,  122 

relation  of  to  respiration,  i,  123 

sphygmographic  tracings,  i,  146,  et  seq. 

variations,  i,  146,  et  seq. 

in  capillaries,  i,  159 
Purkinje's  figures,  ii,  215 
Pylorus,  structure  of,  i,  242 

action  of,  i,  250 
Pyramidal  jiortion  of  kidney,  i,  348 
Pyramids  of  medulla  oblongata,  ii,  106 


Q. 

Quadrui^eds,  retinae  of,  ii,  230 
Ciuanlily  of  air  brealhcd,  i,  XSd 


Quantity  of  blood,  i,  63 
saliva,  i,  229 


R. 

Racemose  glands,  ii,  323 
Radiation  of  impressions,  ii,  85 
Rectum,  ii,  261 
Recurrent  sensibility,  ii,  96 
Reflex  actions,  ii,  85 

acquired,  ii,  87 

augmentation,  ii,  88 

classification,  ii,  86 

compound,  ii,  87 

conditions  necessary  to,  ii,  85 

in  disease,  ii,  102 

examples  of,  ii,  88 

exci to-motor  and  sensori-motor,  ii,  85 
inhibition  of,  ii,  88,  101 
irregular  in  disease,  ii,  102 
after  separation  of  cord  from  brain, 
ii,  100 
laws  of,  i,  373 
morbid,  ii,  102 

of  medulla  oblongata,  ii,  109,  et  seq. 
of  spinal  cord,  ii,  100 
purposive  in  health,  ii,  86 
relation  between  a  stimulus  and,  ii, 
86 

secondary,  ii,  87 

simple,  ii,  87 
Refracting  media  of  eye,  ii,  204 
Refraction,  laws  of,  ii,  204 
Regions  of  bod)^    See  Frontispiece. 
Registering  apparatus, 

cardiograph,  ii,  119 

kymograph,  i,  150 

sphj^gmograph,  i,  143 
Relations  between  secretions,  i,  327 
Reptiles, 

blood-corpuscles,  i,  76 

Drain,  ii,  125 
Reserve  air,  i,  189 
Residual  air,  i,  189 
Respiration,  i,  172 

abdominal  type,  i,  186 

changes  of  air,  i,  194 
of  blood,  i,  197 

costal  type,  i,  186 

force,  i,  191 

frequency,  i,  190 

influence  of  nervous  system,  i,  201 
mechanism,  i,  183,  et  seq. 
movements,  i,  184.    JSee  Respiratory 

^[ovenients. 
nitrogen  in  relation  to,  i,  195 
organic  maltcr  excreted,  i,  196 
quantity  of  air  cluvnged,  i,  189 
relation  to  the  [lulse,  i,  123,  213 
suspension  and  arrest,  i,  209 
types  of,  i,  186 
Respiratorv  capacity  of  chest,  i,  189 
cells,  i,  180 

functions  of  skin,  i,  345 


INDEX. 


371 


Respiratory  movements,  i,  184 
axes  of  rotation,  i,  184,  etseq. 
of  air  tubes,  i,  175 
of  glottis,  i,  188 

influence  on  amount  of  carbonic  acid, 
i.  193 

on  arterial  tension,  i,  213 
rate,  i,  190 
relation  to  pulse  rate,  i,  190 
size  of  animal,  i,  190 
relation  to  will,  i,  201 
various  mechanism,  1,  198 
muscles,  i,  183,  et  seq. 
daily  work,  i,  189 
power  of,  i,  191 
nerve-centre,  i,  202 
rhythm,  i,  188 
sounds,  i,  188 
Restiform  bodies,  ii,  107 
Rete  mucosum,  i,  333 

testis,  ii,  247 
Retiform  or  adenoid,  or  lymphoid  tissue, 

i,  34 
Retina,  ii.  199 

blind-spot,  ii,  215 
blood-vessels,  ii,  203 
,  duration  of  impressions  on,  ii,  216 
of  after-sensations,  ii,  216 
effect  of  pressure  on,  ii,  229 
excitation  of,  ii,  215 
focal  distance,  ii,  206 
fovea  centralis,  ii,  199,  215 
functions  of,  ii,  215 
image  on,  how  formed  distinctly,  ii, 
203 

inversion  of,  how  corrected,  ii,  218 
insensible  at  entrance  of  optic  nerve, 

ii,  215 
layers,  ii,  199 

in  quadrupeds,  ii,  230 
reciprocal  action  of  parts  of,  ii,  226 
in  relation  to  direction  of  vision,  ii, 
222 

to  motion  of  bodies,  ii,  222 

to  single  vision,  ii,  229 

to  size  of  field  of  vision,  ii,  220 

reflection  of  light  from,  ii,  217 

structure  of,  ii,  199 

vessels,  ii,  203 

visual  purple,  ii,  218 
Rheoscopic  frog,  ii,  46 
Rhinencephalon,  ii,  289 
Ribs,  axes  of  rotation,  i,  184,  et  seq. 
Rigor  mortis,  ii,  37 

affects  all  classes  of  muscles,  ii,  37 

phenomena  and  causes  of,  ii,  38 
Rima  glottidis,  movements  of  in  respira- 
tion, i,  188 
Ritter's  tetanus,  ii,  49 
Rods  of  Corti,  il,  184 

use  of,  ii,  192 
Rouleaux,  formation  of  in  telood,  1,  76 
Ruminants 

stomach  of,  i,  240 
Rumination,  i,  240 


Running,  mechanism  of,  ii,  44 
Rut  or  heat,  ii,  240 


S. 

Saccharine  principles  of  food,  digestion 

of,  i,  284 
Sacculus,  ii,  185  , 
Saliva,  i,  229 

composition,  i,  229 

process  of  secretion,  i,  235 

quantity,  i,  230 

rate  of  secretion,  i,  230 

uses,  i,  230 
Salivary  glands,  i,  226 

development  of,  ii,  297 

influence  of  nervous  system,  i,  231 

mixed,  i,  229 

nerves,  i,  229 

secretion,  i,  228 

structure,  i,  226 

true,  i,  227 

varieties,  i,  227 
Sarcode,  i,  5.    See  Protoplasm. 
Sarcolemma,  ii,  16 
Sarcosin,  ii,  332 
Sarcous  elements,  ii,  17 
Scala  media,  ii,  183 

tympani,  ii,  183 

vestibuli,  ii,  183 
Sclerotic,  ii,  197 

blood-vessels,  ii,  203 
Scurvy  from  want  of  vegetables,  i,  217 
Sebaceous  glands,  i,  337 

their  secretion,  i,  343 
Sebacic  acid,  ii,  340 
Secreting  glands,  i,  322 

aggregated,  ii,  323 

convoluted  tubular,  ii,  323 

tubular  or  simple,  ii,  323 
Secreting  membranes,  i,  319.    See  Mu- 
cous and  Serous  membranes. 
Secretion,  i,  318 

apparatus  necessary  for,  i,  318,  et  seq. 

changes  in  gland-cells  during,  i,  326 
"       "  pancreas,  i,  265 
"  stomach,  i,  244 
"       '*  salivary  glands,  i,  234 

circumstances  influencing,  i,  326 

discharge  of,  i,  326 

general  nature  of,  i,  318 

influence  of  nervous  system,  i,  327 

process  of  physical  and  chemical,  i, 
324,  325 

serous,  i,  320 

synovial,  i,  321 
Segmentation  of  cells,  ii,  252 

ovum,  ii,  252 
Semen,  ii,  251 

composition  of,  ii,  251 

emission  of,  a  reflex  act,  ii,  103 

filaments  or  spermatozoa,  ii,  247 
purpose  of,  ii,  251 

tubes,  ii,  247 


372 


ESTDEX. 


Semicircular  canals  of  ear,  ii,  183 

development  of,  ii,  294,  et  seq. 

use  of,  ii,  191 
Semilunar  valves,  i,  106 

functions  of,  i,  114 
Semilunes  of  Heidenhain,  i,  228 
Sensation,  ii.  158 

color,  ii,  223 

common,  ii,  158 

conditions  necessary  to,  ii,  159 

excited  by  mind,  ii,^  159 
by  internal  causes,  ii,  160 

of  motion,  ii,  161 

nerves  of,  ii,  136,  et  seq. 
impressions  on  referred  to  periphery, 
ii,  79 

laws  of  action,  ii,  80 
objective,  ii,  160 
of  pain,  ii,  162 
of  pressure,  ii,  165 
special,  ii,  159 

nerves  of,  ii,  137 
•   stimuli  of,  ii,  82 

of  special,  ii,  82 
subjective,  ii,  83,  168.  See  also  Special 

Senses,  ii,  160 
tactile,  ii,  166 
temperature,  ii,  168 
tickling,  ii,  162 
touch,  ii,  162 

transference  and  radiation  of,  ii,  83,  et 
seq. 

of  weight,  ii,  166 
Sense,  special,  ii,  158 

of  hearing,  ii,  179.  >S^e  Hearing,  Sound. 

of  sight,  ii,  196.    See  Vision. 

of  srnell,  ii,  175.    See  Smell. 

of  taste,  ii,  168.    See  Taste. 

of  touch,  ii,  162.    See  Touch. 

muscular,  ii,  165 

organs  of,  development  of,  ii,  291 
Sensory  impressions,  conduction  of,  ii,81 
by  spinal  cord,  ii,  97 

nerves,  ii,  81 
Septum  between  auricles,  formation  of, 
ii,  280 

between  ventricles,   formation  of,  ii, 
280 

Serous  fluid,  i,  320 
Serous  membranes,  i,  319 

arrangement  of,  i,  319 

communication  of  lymphatics  with,  i, 
294 

epithelium,  i,  319 

fluid  .secreted  by,  i,  320 

functions,  i,  320 

lining  joints,  etc.,  i,  320 
visceral  cavities,  i,  320 

stomata,  i,  294 

structure  of,  i,  319 
Serum, 

of  blood,  i,  93 

separation  of,  i,  66,  93 
Seventh  cerebral  nerve,  auditory  portion, 
ii,  185 


Seventh  cerebral  nerve,  facial  portion, 
ii,  144 

Sex,  influence  on  blood,  i,  87 
influence  on  production  of  carbonic 

acid,  i,  193 
relation  to  respiratory  movements,  i, 
186 

Sexual  organs  and  functions  in  the  fe- 
male, ii,  234 
in  the  male,  ii,  246 
Sexual  passion,  connection  of  with  cere- 

beflum,  ii,  119 
Sighino;,  mechanism  of,  ii,  199 
i  Sight,  li,  196.    See  Vision. 
'  Silica,  parts  in  which  found,  ii,  342 
,  Silicon,  ii,  342 

1  Singing,  mechanism  of,  i,  201;  ii,  56,  et 
seq. 

Single  vision,  conditions  of,  ii,  229 
Sinus  pocularis,  ii,  304 
urogenitalis,  ii,  304 
i  Sinuses  of  dura  mater,  i,  167 
Sixth  cerebral  nerve,  ii,  143 
Size  of  field  of  vision,  ii,  220 
Skeleton.    See  Frontispiece. 
Skin,  i,  333 
absorption  by,  i,  345  ' 
of  metallic  substances,  i,  345 
of  water,  i,  346 
cutis  vera  of,  i,  335 
epidermis  of,  i,  333 
evaporation  from,  i,  313 
I     excretion  by,  i,  344 
I     exhalation  of  carbonic  acid  from,  i,  344 
of  watery  vapor  from,  i,  344 
functions  of,  i,  342 
i        respiratory,  i,  345 
i     papillie  of,  1,  335 
perspiration  of,  i,  343 
rete  mucosnm  of,  i,  334 
sebaceous  glands  of,  i,  336 
;      structure  of.  i,  333 

sudoriparous  glands  of,  i,  337 
Sleep,  ii,  135 
Smefl,  sense  of.  ii,  175 
conditions  of,  ii,  175 
delicacy,  ii,  177 
different  kinds  of  odors,  11,  178 
I     impaired  by  lesion  of  facial  nerve,  ii, 
144 

impaired  by  lesion  of  fifth  nerve,  11, 
141 

internal  excitants  of,  ii.  179 
limited  to  olfactory  region,  i.  176 
relation  to  common  sensibility,  ii,  178 
structure  of  organ  of,  ii,  176 
subjective  sensations,  ii.  179 
varies  in  different  animals,  ii,  178 
Sneezing,  caused  by  sun's  Hght,  ii,  84 

mechanism  of.  i.  200 
Snifling,  mechanism  of.  i,  201 
smell,  aided  by.  ii,  176 

;  Sobbing,  i,  201  ' 

i  Sodium,  ii,  342 

,      in  human  body,  ii,  342 


INDEX. 


373 


Sodium,  salts  of  in  blood,  i,  85 
Solitary  glands,  i,  258 
Soluble  ferments,  ii,  335* 
Somatopleure,  ii,  259 
Somnambulism,  ii,  87 
Sonorous  vibrations,  how  communicated 
in  ear,  ii,  186,  et  seq. 
in  air  and  in  water,  ii,  186.  See  Sound. 
Soprano  voice,  ii,  57 
Sound, 
binaural  sensations,  ii,  195 
conduction  of  by  ear,  ii,  186 
by  external  ear,  ii,  186 
by  internal  ear,  ii,  191 
movements  and  sensations  produced 

by,  ii,  196 
perception, 

of  direction  of,  ii,  194 
of  distance  of,  ii,  194 
permanence  of  sensation  of,  ii,  195 
produced  by  contraction  of  muscle,  ii, 
35 

production  of,  ii,  193 

subjective,  ii,  195 
Source  of  water,  ii,  341* 
Spasms,  reflex  acts,  ii,  103 
Speaking,  ii,  60 

mechanism  of,  i,  200;  ii,  60 
Special  senses,  ii,  159 
Spectrum-analysis  of  blood,  i,  92 
Spectrum  or  ocular  after-sensation,  ii,  225 
Speech,  ii,  60 

function  of  tongue  in,  ii,  62 

influence  of  medulla  oblongata  on,  ii, 
111 

Spermatozoa,  development  of,  ii,  247 

form  and  structure  of,  ii,  248 

function  of,  ii,  251 

motion  of,  ii,  251 
Spherical  aberration,  ii,  212 

correction  of,  ii,  213 
Spheroidal  epithelium,  i,  23 
Sphincter  ani,  i,  263,  288 

external,  i,  288 

internal,  1,  263 

influence  of  spinal  cord  on,  i,  288 
Sphygmograph,  i,  143 

tracings,  i,  145,  et  seq. 
Spinal  accessory  nerve,  ii,  149 
Spinal  cord,  ii,  90 

aiitomatism,  i,  105 

canal  of,  ii,  90 

centres  in,  ii,  103 

a  collection  of  nervous  centres,  ii,  103 

columns  of,  ii,  91 

commissures  of,  ii,  91 

conduction  of  impressions  by,  ii,  97,  et 

seq. 

course  of  fibres  in,  ii,  95 
decussation  of  sensory  impressions  in, 
ii,  99 

effects  of  injuries  of,  on  conduction  of 
impressions,  ii,  99,  et  seq. 
on  nutrition,  ii,  157 
fissures  and  furrows  of,  ii,  90 


Spinal  cord,  functions  of,  ii,  97 
of  columns,  ii,  99 
influence  on  lymph-hearts,  ii,  103 
on  sphincter  ani,  ii,  103 
on  tone,  ii,  104 
morbid  irritability  of,  ii,  103 
nerves  of,  ii,  93 
reflex  action  of,  ii,  100 
in  disease,  ii,  102 
inhibition  of,  ii,  101 
size  of  different  parts,  ii,  91 
special  centres  in,  ii,  103 
structure  of,  ii,  90,  et  seq. 
transference,  ii,  100 
weight,  ii,  126 

relative,  ii,  126 
white  matter,  ii,  91 
grey  matter,  ii,  92 
Spinal  nerves,  ii,  94,  150 
origin  of,  ii,  94 
physiology  of,  ii,  96 
Spiral  canal  of  cochlea,  ii,  182 
lamina  of  cochlea,  ii,'  182 
function  of,  ii,  188 
Spirometer,  i,  189 
Splanchnic  nerve,  i,  154,  252 
Splanchnopleure,  ii,  259 
Spleen,  ii,  1 
functions,  ii,  4 
hilus  of,  ii,  1 

influence  of  nervous  system,  ii,  5 

Malpighian  corpuscles  of,  ii,  3 

pulp,  ii,  2 

stroma  of,  ii,  2 

structure  of,  ii,  2 

trabeculge  of,  ii,  2 
Splenic  vein,  blood  of,  1,  88 
Spot,  germinal,  ii,  237 
Squamous  epithelium,  i,  20 
Stammering,  ii,  62 
Stapedius  muscle,  ii,  181 

function  of,  ii,  191 
Stapes,  ii,  181 
Starch,  i,  231 

digestion  of 
in  small  intestine,  i,  267,  285 
in  mouth,  i,  231 
in  stomach,  i,  248,  285 
Starvation,  i,  219 

appearances  after  death,  i,  220 

effect  on  temperature,  i,  220 

loss  of  weight  in,  i,  219 

period  of  death  in,  i,  220 

symptoms,  i,  220 
Steapsin,  i,  267 
Stearic  acid,  ii,  339 
Stearin,  ii,  338 
Stercorin,  i,  278 

allied  to  cholesterin,  i,  278 
Stereoscope,  ii,  222 
St.  Martin,  Alexis,  case  of,  ii,  245 
Stomach,  i,  240 

blood-vessels,  i,  244 

development,  ii,  295,  et  seq. 

digestion  in,  i,  245 


374 


ESTDEX. 


Stomach,  circumstances  favoring  diges- 
tion in,  i,  248 

products  of,  i,  247 
digestion  after  death,  i,  253 
glands,  i,  242 
lymphatics,  i,  244 
movements,  i,  249 

influence  of  nervous  system,  1,  252 
mucous  membrane,  i,  241 
m.uscular  coat,  i,  241 
nerves,  i,  248 
ruminant,  i,  240 

secretion  of,  i,  245.    See  Gastric  fluid, 
structure,  i,  241 
temperature,  i,  245 
Stomata,  i,  160,  295 

Stratum  intermedium  (Hannover),  i,  60 
Striated  muscle,  ii,  15 
Stromlihr,  i,  164 

Structural  basis  of  human  body,  i,  5 
Stumps,  sensations  in,  ii,  82 
Succinic  acid,  ii,  340 
Succus  entericus,  i,  283 

functions  of,  i,  283 
Sucking,  mechanism  of,  i,  201 
Sudoriferous  glands,  i,  337 

their  distribution,  i,  338 

number  of,  i,  338 

their  secretion,  1,  343 
Suffocation,  i,  208,  et  seq. 
Sugar,  ii,  339 

as  food,  experiments  with,  i,  221 

digestion  of,  i,  284,  286 

formation  of  in  liver,  1,  280,  282 
Sulphates,  ii,  342 

in  tissues,  ii,  342 

in  urine,  i,  163 
Sulphuretted  hydrogen,  ii,  341 
Suprarenal  capsules,  ii,  8 

development  of,  ii,  302 

disease  of,  relation  to  discoloration  of 
skin,  ii,  10 
Structure,  ii,  8 

Sun,  a  source  of  energy,  ii,  310 
Swallowing,  i,  238 

nerves  engaged,  i,  239 
Sweat,  i,  343 

Sympathetic  nervous  system,  ii,  151 
character    of    movements  executed 

through,  ii,  154 
conduction  of  impressions  b}^  ii,  153 
diagrammatic  view,  ii,  152 
distribution,  ii,  151 
divisions  of,  ii,  68 

fibres,  differences  of    from  cerebro- 
spinal fibres,  ii,  72 
mixture  willi  cerebro-spinal  fibres,  ii, 
151 

functions,  ii,  153 
ganglia  of,  ii,  154 

action  of,  ii,  154,  ct  seq. 

co-ordination  of  movements  by,  ii, 
155 

structure,  ii,  151 

in  substance  of  organs,  ii,  155 


Sympathetic  nervous  system,  influence 
on  animal  heat  of,  ii,  316 
blood-vessels,  i,  153,  et  seq. 
heart,  i,  128 
intestines,  i,  289 

involuntary  motion,  ii,  154,  et  seq. 
salivary  glands,  i,  231,  et  seq. 
secretion,  i,  231 
stomach,  i,  252 
structure  of,  ii,  151 
Synovial  fluid,  secretion  of,  i,  321 

membranes,  i,  321 
Syntonin,  i,  248;  ii,  328 
Systemic  circulation,  i,  101.    See  Circu- 
lation, 
vessels,  i,  101 
Systole  of  heart,  i,  119 


T. 

Taste,  ii,  168 
after-tastes,  ii,  174 
conditions  for  perception  of,  ii,  168 
connection  with  smell,  ii,  174 
impaired  by  injury 

of  facial  nerve,  ii,  145 

of  fifth  nerve,  ii,  142 
nerves  of,  ii,  142,  146 
seat  of,  ii,  168 

subjective  sensations,  ii,  175 

varieties,  ii,  174 
Taste-goblets,  ii,  173 
Taurin,  ii,  332 
Taurocholic  acid,  1,  274 
Teeth,  i,  55 

development,  ii,  58 

eruption,  times  of,  i,  62 

structure  of,  i,  55,  et  seq. 

temporary  and  permanent,  i,  61,  et  seq. 
Temperament,  influence  on  blood,  i.  87 
Temperature,  i,  309 

average  of  body,  i,  309 

changes  of,  effects  of,  i,  310,  et  seq. 

circumstances  modifying,  i,  312 

of  cold-blooded  and  warm-blooded  ani- 
mals, i,  311 

in  disease,  i,  311 

influence  on  amount  of  carbonic  acid 

produced,  i,  194 
loss  of,  i,  313 
maintenance  of,  i,  313 
of  Mammalia,  Birds,  etc.,  i,  311 
of  paralyzed  parts,  i,  316 
regulation  of,  i.  313 
of  respired  air,  i,  196 
sensation  of  variation  of,  ii,  166.  See 

Heat. 

Tendons,  structure  of,  i,  32 

cells  of,  i,  32 
Tenor  voice,  ii,  57 
Tension,  arterial,  i,  148 
Tension  of  gases  in  lungs,  i,  197 
Tensor  tvniiKuii  muscle,  ii,  181 

oflice  of,  ii,  190 


INDEX. 


375 


Tessellated  epithelium,  i,  19 
Testicle,  ii,  246 

development,  ii,  300 

descent  of,  ii,  302 

structure  of,  ii,  246,  et  seq. 
Tetanus,  ii,  32 
Tlialamencephalon,  ii,  289 
Thalami  optici,  functions  of,  ii,  115 
Thermogenic  nerves  and  nerve-centres,  i, 
3i6 

Thirst,  i,  219 

allayed  by  cutaneous  absorption,  i,  345 
Thoracic  duct,  i,  291 

contents,  i,  302 
Thymus  gland,  ii,  5 

function  of,  ii,  6 

structure,  ii,  5 
Thyro-arytenoid  muscles,  ii,  58 
Thyi  oid  cartilage,  structure  and  connec- 
tions of,  ii,  52 
Thyroid-gland,  ii,  7 

function  of,  ii,  8 

structure,  ii,  7 
Timbre  of  voice,  ii,  57 
Tissue,  adipose,  i,  35 

areolar,  cellular,  or  conneciive,  i,  31 

elastic,  i,  32 

fatty,  i,  35 

fibrous,  i,  32 

gelatinous,  i,  33 

retiform,  i,  34 
Tissues, 

connective,  i,  28 

elementary  structure  of,  1,  28,  et  seq. 

erectile,  i,  168 
Tone  of  blood-vessels,  i,  153 

of  muscles,  ii,  104 

of  voice,  ii,  57 
Tongue,  ii,  169 

action  of  in  deglutition,  i,  238 
in  sucking,  i,  201 

action  of  in  speech,  ii,  62 

epithelium  of,  ii,  72 

influence  of  facial  nerve  on  muscles  of, 
ii,  145 

motor  nerve  of,  ii,  150 

an  organ  of  touch,  ii,  173 

papillae  of,  ii,  169 

parts  most  sensitive  to  taste,  ii,  l'^4 

structure  of,  ii,  169 
Tonsils,  i,  236 
Tooth,  i,  55.    See  Teeth. 
Tooth-ache,  radiation  of,  sensation  in,  ii, 
85 

Tooth-pulp,  i,  55 

Touch,  ii,  162 
after  sensation,  ii,  168 
conditions  for  perfection  of,  ii,  163 
connection  of  with  muscular  sense,  ii, 
165 

co-operation  of  mind  with,  ii,  167 
function  of  cuticle  with  regard  to,  i, 
333 

of  papillae  of  skin  with  regard  to,  i, 
333 


Touch,  hand  an  organ  of,  ii,  163 
illusions,  ii,  165 
modifications  of,  ii,  162 
a  modification  of  common  sensation,  ii, 
162 

special  organs,  ii,  163 
subjective  sensations,  ii,  IGS 
the  tongue  an  organ  of,  ii,  164 
various  degrees  of  in  different  parts,  ii, 
164 

Touch-corpuscles,  i,  336 
Ti  abeculse  cranii,  ii,  273 
Trachea,  i,  175 

Tradescantia  Virginica,  movements  in 

cells  of,  i,  7 
Tragus,  ii,  179 

Transference  of  impressions,  ii,  84 
Traube-Hering's  curves,  i,  209 
Tricuspid  valve,  i,  109 

safety-valve  action  of,  i,  113 
Trigeminal  or  fifth  nerve,  ii,  139 

effects  of  injury  of,  ii,  140 
Trophic  nerves,  ii,  142 
Trypsin,  i,  267 
Trypsinogen,  i,  266 
Tube,  Eu^tacbian,  ii,  180 
Tubercle  of  Lower,  i,  105 
Tubes,  Fallopian,  ii,  238.    See  Fallopian 
Tubes. 

looped,  of  Henle,  i,  350 
Tubular  glands,  i,  323 

convoluted,  i,  323 

simple,  i,  323 

of  intestines,  i,  257,  263 

of  stomach,  i,  242 
Tubules,  i,  17 
Tubuli  seminiferi,  ii,  247 

uriniferi,  i,  348,  etseq. 
Tunica  albuginea  of  testicle,  ii,  246 
Tympanum  or  middle  ear,  ii,  180 

development  of,  ii,  293 

functions  of,  ii,  187 

membrane  of,  ii,  180 

structure  of,  ii,  180 

use  of  air  in,  ii,  189 
Types  of  respiration,  i,  186 
Tyrosin,  i,  266 


U. 

Ulceration  of  parts  attending  injuries  of 

nerves,  ii,  156 
Ulnar  nerve, 

eff'ects  of  compression  of,  ii,  81 
Umbilical  arteries,  ii,  270 

contraction  of,  i,  142 

cord,  ii,  270 

vesicle,  ii,  254,  261 
Unconscious  cerebration,  ii,  130 
Unorganized  ferments,  ii,  335 
Unstriped  muscular  fibre,  ii,  14 

development,  ii,  20 

distribution,  ii,  14 

structure,  ii,  15 


376 


Urachus,  ii,  264 

Urate  of  ammonium,  i,  360 

of  sodium,  i,  360 
Urea,  i,  358 

apparatus  for  estimating  quantity,  i, 
359 

chemical  composition  of,  i,  395 
identical  with  cyanate  of  ammonium, 

i,  359 
properties,  i,  358 
quantity,  i,  359 

in  relation  to  muscular  exertion,  i,  371 

sources,  i,  370 
Ureides,  ii,  333 
Ureter,  i,  354 

Urethra,  development  of,  ii,  305 
Uric  acid,  i,  360 

condition  in  which  it  exists  in  urine,  i, 
360 

forms  in  which  it  is  deposited,  i,  361 
proportionate  quantity  of,  i,  360 
source  of,  i,  372 
tests,  i,  361 

variations  in  quantity,  i,  360 
Urina  sanguinis,  potus,  et  cibi,  i,  357 
Urinary  bladder,  i,  349 

development,  ii,  302 

nerves,  i,  353 

regurgitation  from  prevented,  i,  373 
structure,  i,  349 
Urinary  ferments,  i,  355;  ii,  338 
abnormal,  i,  358 
analysis  of,  i,  355 
chemical  composition,  i,  355 
coloring  matter  of,  i,  362 
cystin  in,  i,  365 

decomposition  by  mucus,  i,  356 

effect  of  blood  pressure  on,  1,  367 

expulsion,  i,  373 

extractives,  i,  363 

flow  of  into  bladder,  i,  372 

gases,  i,  365 

hippuric  acid  in,  i,  361 

mucus  in,  i,  362 

oxalic  acid  in,  i,  365 

physical  characters,  i,  355 

pigments,  i,  362 

quantity  of  chief  constituents,  i,  356 
reaction  of,  i,  355 

in  different  animals,  i.  356 

made  alkaline  by  diet,  i,  356 
saline  matter,  i,  363 
secretion,  i,  370 

effects  of  posture,  etc.,  on,  i,  373 

rate  of,  i,  373 
solids,  i,  358 

variations  of,  i,  356 
specific  gravity  of,  i,  357 

variations  of,  i,  357 
urates,  i,  360,  361 
urea,  i,  358 
uric  acid  in,  i,  360 
variations  of  specilic  gravity,  1,  357 

of  water,  i,  357 
Urobilin,  i,  362 


Urochrome,  i,  362 
Uroerythrin,  i,  362 
Uses  of  blood,  i,  91 
Uterus,  ii,  238 

change  of  mucous  membrane  of,  ii,  242 

development  of  in  pregnancy,  ii,  242 

follicular  glands  of,  ii,  239 

masculinus,  ii,  304 

reflex  action  of,  ii,  103 

structure,  ii,  238 
*  Utriculus  of  labyrinth,  ii,  185 
Uvula  in  relation  to  voice,  ii,  59 

V. 

Vagina,  structure  of,  ii,  239 

Vagus  nerve,  i,  232.    See  Pneumogastric. 

Valerianic  acid,  ii,  339 

Valve,  ilio-csecal,  structure  of,  i,  263 

of  Vieussens,  ii,  115 
Valves  of  heart,  i,  109 

action  of,  i,  112,  etseq. 

bicuspid  or  mitral,  i,  109  * 

semilunar,  i,  110, 114 

tricuspid,  i,  109,  110 

of  lymphatic  vessels,  i,  297 

of  veins,  i,  137,  et  seq. 
Valvulse  conniventes,  i,  255 
Vas  deferens,  ii,  246 

development,  ii,  300 
Vasa  efferentia  of  testicle,  ii,  247 
of  kidney,  i,  353 

recta  of  kidney,  i,  353 
of  testicle,  ii,  247 

vasorum,i,  131 
Vascular  area,  ii,  262 
Vascular  glands,  ii,  461 

in  relation  to  blood,  ii,  11 

several  oflices  of,  ii,  11 
Vascular  system,  development  of,  ii,  276 
Vaso-coustrictor  nerves,  i,  156 
Vaso-dilator  nerves,  i,  156 
Vaso-motor  influence  on  blood-pressure, 

i,  154,  seq. 
Vaso-motor  nerves,  i,  154 

effect  of  section,  i,  154,  ci  seq. 

influence  upon  blood-pressure,  i,  154 
Vaso-motor  nerve-centres,  i,  154 

reflection  by,  i,  154 
Vegetables  and  animals,  distinctions  be- 
tween, i,  3 
Veins,  i,  135 

anastomoses  of,  i,  162 

blood-pressure  in,  i,  162 

circulation  in,  i,  161,  et  seq. 
rate  of,  i.  166 

cardinal,  ii,  284 

collateral  circulation  in,  i,  161 

cranium,  i,  167 

develoiiment,  ii,  283 

distribution,  ii,  135 

effects  of  muscular  ju'cssuro  on,  i,  162 
of  ri'spiration  on,  i.  206 

force  of  heart's  action  remaining  in,  i, 
162 


INJ)EX. 


Veins,  iiilliience  of  expiration  on,  i,  207 
inspiration,  i,  206 

influence  of  gravitation  in,  i.  163 

parietal  system  of,  ii,  283,  et  seq. 

pressure  in,  i,  162 

rliythmical  action  in,  i,  162 

structure  of,  i,  136 

systemic,  i,  102 

umbilical,  ii,  270 

valves  of,  i,  137 

velocity  of  blood  in,  i,  165 

visceral  system  of,  ii,  283,  et  seq. 
Velocity  of  blood  in  arteries,  i,  164 
in  capillaries,  i,  165 
in  veins,  i,  165 

of  circulation,  i,  163 

of  nervous  force,  ii,  81 
Venaportae,  i,  88,  269 
Venai  hepaticse  advehentes,  ii,  283 

revehentes,  ii,  284 
Ventilation,  i,  204 
Ventricles  of  heart,  i,  112 

capacity  of,  i,  107 

contraction  of,  i,  112 
effect  on  blood-current  in  veins,  i,  124 

dilatation  of,  i,  124 

force  of,  i,  124 

of  larynx,  office  of,  ii,  60 
Ventriloquism,  ii,  62,  194 
Vermicular  movement  of  intestines,  i, 
289 

Vermiform  process,  i,  262 
Vertebra?,  development  of,  ii,  270 
Vesicle,  germinal,  ii,  237 

Graafian,  ii,  285 
bursting  of,  ii,  240 

umbilical,  ii,  254,  261 
Vesicula  germinativa,  ii,  237 
Vesiculae  seminales,  ii,  250 

functions  of,  ii,  250 

reflex  movements  of,  ii,  103 

structure,  ii,  250 
Vestibule  of  the  ear,  ii,  182 
Vestigial  fold  of  Marshall,  ii,  285 
Vibrations,  conveyance  of  to  auditory 
nerve,  ii,  185,  et  seq. 

perception  of,  ii,  194 

of  vocal  cords,  ii,  52 
Vidian  nerve,  ii,  144 
Villi  in  chorion,  ii,  265 

in  placenta,  ii,  268 
Villi  of  intestines,  i,  259 

action  in  digestion,  i,  260 
Visceral  arches,  development  of,  ii,  273 

connection  with  cranial  nerves,  ii,  274 

lamina?  or  plates,  ii,  260 
Vision,  ii.l96 

angle  of,  ii,  221 

at  different  distances,  adaptation  of  eye 

to,  ii,  207,  et  ^eq. 
contrasted  with  touch,  ii,  221 
corpora  quadrigemina,   the  principal 

nerve-centres  of,  ii,  114 
correction  of  aberration,  ii,  213,  et  seq. 
of  inversion  of  image  in,  ii,  218 


Vision,  defects  of,  ii,  211,  et  seq. 
distinctness  of,  how  secured,  ii,  203,  et 
seq. 

double,  ii,  229 

duration  of  sensation  in,  ii,  216 
estimation  of  the  form  of  objects,  ii,  222 

of  their  direction,  ii,  222 

of  their  motion,  ii,  222 

of  their  size,  ii,  221 
field  of,  size  of,  ii,220 
focal  distance  of,  ii,  206 
impaired  by  lesion  of  fifth  nerve,  ii, 
140 

influence  of  attention  on,  ii,  223 
modified  by  ditt'erent  parts  of  the  ret- 
ina, ii,  226 
purple,  ii,  218 
in  quadrupeds,  ii,  230 
single,  with  two  eyes,  ii,  231 
Visual  direction,  ii,  222 
Vital  or  respiratory  capacity  of  chest,  i, 
189 

Vital  capillarv  force,  i,  161 
Vital  force,  ii",  321 
Vitellin,  ii,  329 
Vitelline  duct,  ii,  261 

membrane,  ii,  237 

spheres,  ii,  253 
Vitreous  humor,  ii,  205 
Vocal  cords,  ii,  52 

action  of  in  respiratory  actions,  i,  188, 
et  seq. 

approximation  of,  effect  on  height  of 

note,  ii,  56 
elastic  tissue  in,  i,  33 
longer  in  males  than  in  females,  ii,  57 
position  of,  how  modified,  ii,  56 
vibrations  of,  cause  voice,  ii,  51 
Voice,  ii,  50,  57 
of  boys,  ii,  58 
compass  of,  ii,  57 

conditions  on  which  strength  depends, 
ii,  58 

Voice,  human,  produced  by  vibration  of 
vocal  cords,  ii,  50,  55 
in  eunuchs,  ii,  58 
influence  of  age  on,  ii,  58 

of  arches  of  palate  and  uvula,  ii,  59 
of  epiglottis,  ii,  55 
of  sex,  ii,  57 
influence  of  ventricles  of  larynx,  ii,  60 

of  vocal  cords,  ii,  56 
in  male  and  female,  ii,  57 

cause  of  different  pitch,  ii,  57 
modulations  of.  ii,  57 
natural  and  falsetto,  ii,  58 
peculiar  chai'acters  of,  ii,  57 
varieties  of,  ii,  58 
Vomiting,  i,  251 
action  of  stomach  in,  i,  251 
nerve  actions  in,  i,  252 
voluntary  and  acquired,  i,  252 
Vowels  and  consonants,  ii,  60 
Vulvo-vaginal  or  Duverney's  glands,  ii, 
239 


w. 

Walkint^j,  ii,  41 
Water,  ii,  841 
absorbed  by  skin,  i,  345 

by  stomach,  i,  284 
amount, 

in  -blood,  variations  in,  82,  87 
exhaled  from  lungs,  i,  195 

from  skin,  i,  845 
forms  large  part  of  human  body,  ii, 
341 

influence  of  on  coagulation  of  blood,  i, 
71 

influence  of  on  decomposition,  ii,  326 
in  urine,  excretion  of,  i,  365 

variations  in,  i,  357 
loss  of  from  body,  ii,  341 

uses,  ii,  341 
quantity  in  various  tissues,  ii,  341 
source,  ii,  341 

vapor  of  in  atmosphere,  i,  192 
Wave  of  blood  causing  the  pulse,  i,  142 

velocity  of,  i,  143 
AVhite  corpuscles,  i,  79.    See  Blood  cor- 
puscles, white;  and  Lymph-cor- 
puscles. 
Wiiite  fibro- cartilage,  i,  41 
til)rous  tissue,  i,  31 


EX. 


Willis,  circle  of,  i,  167 
Wolflian  bodies,  ii,  398,  et  seq. 
Work  of  heart,  i,  124 


X. 

Xanthin,  i,  363 

Xantho-proteic  reaction,  ii,  327 


Y 

Yawning,  1,  201 

Yelk,  or  vitellus,  ii,  252 

changes  of,  in  Fallopian  tube,  ii,  253 

cleaving  of,  ii,  253 

constriction  of,  by  ventral  laminai,  ii, 
260 

Yelk-sac,  ii,  260,  seq. 
Yellow  elastic  flbre,  i,  30,  33 

fibro-cartilage,  i,  40 

spot  of  iSommering,  ii,  199 
Young-Hehnholtz  theory,  ii,  224 

Z. 

Zimmermann,  corpuscles  of,  ii,  6 
Zona  pellucidu,  ii,  287 


si 


